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  • How to check if the tab page is dirty and prompt the user to save before navigating away using ajaxtoolkit tab control in ASP.NET

    Step 1: Put a hidden variable in Update panel <asp:HiddenField ID="hfIsDirty" runat="server" Value="0" /> Step 2: Put the following code in ajaxcontrol tool kit tabcontainer OnClientActiveTabChanged="ActiveTabChanged" Copy the following script in the aspx page. <script type="text/javascript">       //Trigger Server side post back for the Tab container       function ActiveTabChanged(sender, e) {           __doPostBack('<%= tcBaseline.ClientID %>', '');       }       //Sets the dirty flag if the page is dirty       function setDirty() {           var hf = document.getElementById("<%=hfIsDirty.ClientID%>");           if (hf != null)               hf.value = 1;       }       //Resets the dirty flag after save       function clearDirty() {           var hf = document.getElementById("<%=hfIsDirty.ClientID%>");           hf.value = 0;       }       function showMessage() { return "page is dirty" }       function setControlChange() {           if (typeof (event.srcElement) != 'undefined')           { event.srcElement.onchange = setDirty; }       }       function checkDirty() {           var tc = document.getElementById("<%=tcBaseline.ClientID%>");           var hf = document.getElementById("<%=hfIsDirty.ClientID%>");           if (hf.value == "1") {               var conf = confirm("Do you want o loose unsaved changes? Please Cancel to stay on page or OK to continue ");               if (conf) {                   clearDirty();                   return true;               }               else {                   var e = window.event;                   e.cancelBubble = true;                   if (e.stopPropagation) e.stopPropagation();                   return false;               }           }           else               return true;       }       document.body.onclick = setControlChange;       document.body.onkeyup = setControlChange;       var onBeforeUnloadFired = false;       // Function to reset the above flag.       function resetOnBeforeUnloadFired() {           onBeforeUnloadFired = false;       }       function doBeforeUnload() {           var hf = document.getElementById("<%=hfIsDirty.ClientID%>");           // If this function has not been run before...           if (!onBeforeUnloadFired) {               // Prevent this function from being run twice in succession.               onBeforeUnloadFired = true;               // If the form is dirty...               if (hf.value == "1") {                   event.returnValue = "If you continue you will lose any changes that you have made to this record.";               }           }           window.setTimeout("resetOnBeforeUnloadFired()", 1000);       }       if (window.body) {           window.body.onbeforeunload = doBeforeUnload;       }       else           window.onbeforeunload = doBeforeUnload;   </script> Step 3: Here is how the tabcontrol should look like <asp:UpdatePanel ID="upTab" runat="server" UpdateMode="conditional">                     <ContentTemplate>                         <ajaxtoolkit:TabContainer ID="tcBaseline" runat="server" Height="400px" OnClientActiveTabChanged="ActiveTabChanged">                             <ajaxtoolkit:TabPanel ID="tpPersonalInformation" runat="server">                                 <HeaderTemplate>                                     <asp:Label ID="lblPITab" runat="server" Text="<%$ Resources:Resources, Baseline_Tab_PersonalInformation %>"                                         onclick="checkDirty();"></asp:Label>                                 </HeaderTemplate>                                 <ContentTemplate>                                     <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder> </ContentTemplate>                             </ajaxtoolkit:TabPanel> span.fullpost {display:none;}

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  • Validar Textbox para aceptar solo n&uacute;meros

    - by Jason Ulloa
    Una de las necesidades más habituales en el desarrollo es poder validar los controles Textbox para que solo acepten valore numéricos. En este post eso es lo que haremos, nos apoyaremos en el lenguaje javascript para validar nuestro textbox del lado del cliente. Nuestro primer paso será crear la función JavaScript que hará el trabajo, para ello agregamos las etiquetas de javascript <script type="text/javascript"> </script> Posteriormente dentro de esas etiquetas agregaremos el script que hará el trabajo function ValidNum(e) { var tecla= document.all ? tecla = e.keyCode : tecla = e.which; return ((tecla > 47 && tecla < 58) || tecla == 46); } Por último iremos al code behind de la página y en el evento Load agregaremos un nuevo evento al textbox para que reconozca el script. protected void Page_Load(object sender, EventArgs e) { TextBox1.Attributes.Add("onkeypress", "javascript:return ValidNum(event);"); } Con esto, tenemos el textbox validado para aceptar solo números y el punto.

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  • Why do I have a gnomekeyring.IOError when doing "quickly share"?

    - by Agmenor
    When I want to push my app to Launchpad by doing quickly share --verbose, I get the following Gnome Keyring error: Get Launchpad Settings Traceback (most recent call last): File "/usr/share/quickly/templates/ubuntu-application/share.py", line 101, in <module> launchpad = launchpadaccess.initialize_lpi() File "/usr/lib/python2.7/dist-packages/quickly/launchpadaccess.py", line 91, in initialize_lpi allow_access_levels=["WRITE_PRIVATE"]) File "/usr/lib/python2.7/dist-packages/launchpadlib/launchpad.py", line 539, in login_with credential_save_failed, version) File "/usr/lib/python2.7/dist-packages/launchpadlib/launchpad.py", line 342, in _authorize_token_and_login authorization_engine.unique_consumer_id) File "/usr/lib/python2.7/dist-packages/launchpadlib/credentials.py", line 282, in load return self.do_load(unique_key) File "/usr/lib/python2.7/dist-packages/launchpadlib/credentials.py", line 336, in do_load 'launchpadlib', unique_key) File "/usr/lib/python2.7/dist-packages/keyring/core.py", line 34, in get_password return _keyring_backend.get_password(service_name, username) File "/usr/lib/python2.7/dist-packages/keyring/backend.py", line 154, in get_password items = gnomekeyring.find_network_password_sync(username, service) gnomekeyring.IOError ERROR: share command failed Aborting This used to work, so this means that I already have SSH and GPG configured. This is probably part of the explanation: I have this error when I am connected to this machine through a ssh tunnel with X forwarding. But I don't have it when I have physical access to the computer. Could you please give me some indications on what to do?

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  • jQuery CSS Property Monitoring Plug-in updated

    - by Rick Strahl
    A few weeks back I had talked about the need to watch properties of an object and be able to take action when certain values changed. The need for this arose out of wanting to build generic components that could 'attach' themselves to other objects. One example is a drop shadow - if I add a shadow behavior to an object I want the shadow to be pinned to that object so when that object moves I also want the shadow to move with it, or when the panel is hidden the shadow should hide with it - automatically without having to explicitly hook up monitoring code to the panel. For example, in my shadow plug-in I can now do something like this (where el is the element that has the shadow attached and sh is the shadow): if (!exists) // if shadow was created el.watch("left,top,width,height,display", function() { if (el.is(":visible")) $(this).shadow(opt); // redraw else sh.hide(); }, 100, "_shadowMove"); The code now monitors several properties and if any of them change the provided function is called. So when the target object is moved or hidden or resized the watcher function is called and the shadow can be redrawn or hidden in the case of visibility going away. So if you run any of the following code: $("#box") .shadow() .draggable({ handle: ".blockheader" }); // drag around the box - shadow should follow // hide the box - shadow should disappear with box setTimeout(function() { $("#box").hide(); }, 4000); // show the box - shadow should come back too setTimeout(function() { $("#box").show(); }, 8000); This can be very handy functionality when you're dealing with objects or operations that you need to track generically and there are no native events for them. For example, with a generic shadow object that attaches itself to any another element there's no way that I know of to track whether the object has been moved or hidden either via some UI operation (like dragging) or via code. While some UI operations like jQuery.ui.draggable would allow events to fire when the mouse is moved nothing of the sort exists if you modify locations in code. Even tracking the object in drag mode this is hardly generic behavior - a generic shadow implementation can't know when dragging is hooked up. So the watcher provides an alternative that basically gives an Observer like pattern that notifies you when something you're interested in changes. In the watcher hookup code (in the shadow() plugin) above  a check is made if the object is visible and if it is the shadow is redrawn. Otherwise the shadow is hidden. The first parameter is a list of CSS properties to be monitored followed by the function that is called. The function called receives this as the element that's been changed and receives two parameters: The array of watched objects with their current values, plus an index to the object that caused the change function to fire. How does it work When I wrote it about this last time I started out with a simple timer that would poll for changes at a fixed interval with setInterval(). A few folks commented that there are is a DOM API - DOMAttrmodified in Mozilla and propertychange in IE that allow notification whenever any property changes which is much more efficient and smooth than the setInterval approach I used previously. On browser that support these events (FireFox and IE basically - WebKit has the DOMAttrModified event but it doesn't appear to work) the shadow effect is instant - no 'drag behind' of the shadow. Running on a browser that doesn't support still uses setInterval() and the shadow movement is slightly delayed which looks sloppy. There are a few additional changes to this code - it also supports monitoring multiple CSS properties now so a single object can monitor a host of CSS properties rather than one object per property which is easier to work with. For display purposes position, bounds and visibility will be common properties that are to be watched. Here's what the new version looks like: $.fn.watch = function (props, func, interval, id) { /// <summary> /// Allows you to monitor changes in a specific /// CSS property of an element by polling the value. /// when the value changes a function is called. /// The function called is called in the context /// of the selected element (ie. this) /// </summary> /// <param name="prop" type="String">CSS Properties to watch sep. by commas</param> /// <param name="func" type="Function"> /// Function called when the value has changed. /// </param> /// <param name="interval" type="Number"> /// Optional interval for browsers that don't support DOMAttrModified or propertychange events. /// Determines the interval used for setInterval calls. /// </param> /// <param name="id" type="String">A unique ID that identifies this watch instance on this element</param> /// <returns type="jQuery" /> if (!interval) interval = 200; if (!id) id = "_watcher"; return this.each(function () { var _t = this; var el$ = $(this); var fnc = function () { __watcher.call(_t, id) }; var itId = null; var data = { id: id, props: props.split(","), func: func, vals: [props.split(",").length], fnc: fnc, origProps: props, interval: interval }; $.each(data.props, function (i) { data.vals[i] = el$.css(data.props[i]); }); el$.data(id, data); hookChange(el$, id, data.fnc); }); function hookChange(el$, id, fnc) { el$.each(function () { var el = $(this); if (typeof (el.get(0).onpropertychange) == "object") el.bind("propertychange." + id, fnc); else if ($.browser.mozilla) el.bind("DOMAttrModified." + id, fnc); else itId = setInterval(fnc, interval); }); } function __watcher(id) { var el$ = $(this); var w = el$.data(id); if (!w) return; var _t = this; if (!w.func) return; // must unbind or else unwanted recursion may occur el$.unwatch(id); var changed = false; var i = 0; for (i; i < w.props.length; i++) { var newVal = el$.css(w.props[i]); if (w.vals[i] != newVal) { w.vals[i] = newVal; changed = true; break; } } if (changed) w.func.call(_t, w, i); // rebind event hookChange(el$, id, w.fnc); } } $.fn.unwatch = function (id) { this.each(function () { var el = $(this); var fnc = el.data(id).fnc; try { if (typeof (this.onpropertychange) == "object") el.unbind("propertychange." + id, fnc); else if ($.browser.mozilla) el.unbind("DOMAttrModified." + id, fnc); else clearInterval(id); } // ignore if element was already unbound catch (e) { } }); return this; } There are basically two jQuery functions - watch and unwatch. jQuery.fn.watch(props,func,interval,id) Starts watching an element for changes in the properties specified. props The CSS properties that are to be watched for changes. If any of the specified properties changes the function specified in the second parameter is fired. func (watchData,index) The function fired in response to a changed property. Receives this as the element changed and object that represents the watched properties and their respective values. The first parameter is passed in this structure:    { id: itId, props: [], func: func, vals: [] }; A second parameter is the index of the changed property so data.props[i] or data.vals[i] gets the property value that has changed. interval The interval for setInterval() for those browsers that don't support property watching in the DOM. In milliseconds. id An optional id that identifies this watcher. Required only if multiple watchers might be hooked up to the same element. The default is _watcher if not specified. jQuery.fn.unwatch(id) Unhooks watching of the element by disconnecting the event handlers. id Optional watcher id that was specified in the call to watch. This value can be omitted to use the default value of _watcher. You can also grab the latest version of the  code for this plug-in as well as the shadow in the full library at: http://www.west-wind.com:8080/svn/jquery/trunk/jQueryControls/Resources/ww.jquery.js watcher has no other dependencies although it lives in this larger library. The shadow plug-in depends on watcher.© Rick Strahl, West Wind Technologies, 2005-2011

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  • Retrieve the full ASP.NET Form Buffer as a String

    - by Rick Strahl
    Did it again today: For logging purposes I needed to capture the full Request.Form data as a string and while it’s pretty easy to retrieve the buffer it always takes me a few minutes to remember how to do it. So I finally wrote a small helper function to accomplish this since this comes up rather frequently especially in debugging scenarios or in the immediate window. Here’s the quick function to get the form buffer as string: /// <summary> /// Returns the content of the POST buffer as string /// </summary> /// <returns></returns> public static string FormBufferToString() { HttpRequest Request = HttpContext.Current.Request; if (Request.TotalBytes > 0) return Encoding.Default.GetString(Request.BinaryRead(Request.TotalBytes)); return string.Empty; } Clearly a simple task, but handy to have in your library for reuse. You probably don’t want to call this if you have a massive inbound form buffer, or if the data you’re retrieving is binary. It’s probably a good idea to check the inbound content type before calling this function with something like this: var formBuffer = string.Empty; if (Request.ContentType.StartsWith("text/") || Request.ContentType == "application/x-www-form-urlencoded") ) { formBuffer = FormBufferToString(); } to ensure you’re working only on content types you can actually view as text. Now if I can only remember the name of this function in my library – it’s part of the static WebUtils class in the West Wind Web Toolkit if you want to check out a number of other useful Web helper functions.© Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET  

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  • Using Exception Handler in an ADF Task Flow

    - by anmprs
    Problem Statement: Exception thrown in a task flow gets wrapped in an exception that gives an unintelligible error message to the user. Figure 1 Solution 1. Over-writing the error message with a user-friendly error message. Figure 2 Steps to code 1. Generating an exception: Write a method that throws an exception and drop it in the task flow.2. Adding an Exception Handler: Write a method (example below) to overwrite the Error in the bean or data control and drop the method in the task flow. Figure 3 This method is marked as the Exception Handler by Right-Click on method > Mark Activity> Exception Handler or by the button that is displayed in this screenshot Figure 4 The Final task flow should look like this. This will overwrite the exception with the error message in figure 2. Note: There is no need for a control flow between the two method calls (as shown below). Figure 5 Solution 2: Re-Routing the task flow to display an error page Figure 6 Steps to code 1. This is the same as step 1 of solution 1.2. Adding an Exception Handler: The Exception handler is not always a method; in this case it is implemented on a task flow return.  The task flow looks like this. Figure 7 In the figure below you will notice that the task flow return points to a control flow ‘error’ in the calling task flow. Figure 8 This control flow in turn goes to a view ‘error.jsff’ which contains the error message that one wishes to display.  This can be seen in the figure below. (‘withErrorHandling’ is a  call to the task flow in figure 7) Figure 9

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  • Stage3D: Camera pans the whole screen

    - by Thomas Versteeg
    I am trying to create a 2D Stage3D game where you can move the camera around the level in an RTS style. I thought about using Orthographic Matrix3D functions for this but when I try to scroll the whole "stage" also scrolls. This is the Camera code: public function Camera2D(width:int, height:int, zoom:Number = 1) { resize(width, height); _zoom = zoom; } public function resize(width:Number, height:Number):void { _width = width; _height = height; _projectionMatrix = makeMatrix(0, width, 0, height); _recalculate = true; } protected function makeMatrix(left:Number, right:Number, top:Number, bottom:Number, zNear:Number = 0, zFar:Number = 1):Matrix3D { return new Matrix3D(Vector.<Number>([ 2 / (right - left), 0, 0, 0, 0, 2 / (top - bottom), 0, 0, 0, 0, 1 / (zFar - zNear), 0, 0, 0, zNear / (zNear - zFar), 1 ])); } public function get viewMatrix():Matrix3D { if (_recalculate) { _recalculate = false; _viewMatrix.identity(); _viewMatrix.appendTranslation( -_width / 2 - _x, -_height / 2 - y, 0); _viewMatrix.appendScale(_zoom, _zoom, 1); _renderMatrix.identity(); _renderMatrix.append(_viewMatrix); _renderMatrix.append(_projectionMatrix); } return _renderMatrix; } And the camera is send directly to the GPU with: c3d.setProgramConstantsFromMatrix(Context3DProgramType.VERTEX, 0, cameraMatrix, true); And these are the shaders: ------Vertex Shader------ m44 op, va0, vc0 mov v0, va1.xy mov v0.z, va0.z ------Fragment Shader------ tex ft0, v0, fs0 <2d,linear,nomip> mov oc, ft1 Here is a example and here are two screenshots to show what I mean: How do I only let the inside of the stage3D scroll and not the whole stage?

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  • Best practice settings Effect parameters in XNA

    - by hichaeretaqua
    I want to ask if there is a best practice settings effect parameters in XNA. Or in other words, what exactly happens when I call pass.Apply(). I can imagine multiple scenarios: Each time Apply() is called, all effect parameters are transferred to the GPU and therefor it has no real influence how often I set a parameter. Each time Apply() is called, only the parameters that got reset are transferred. So caching Set-operations that don't actually set a new value should be avoided. Each time Apply() is called, only the parameters that got changed are transferred. So caching Set-operations is useless. This whole questions is bootless because no one of the mentions ways has any noteworthy impact on game performance. So the final question: Is it useful to implement some caching of Set-operation like: private Matrix _world; public Matrix World { get{ return _world;} set { if(value == world)return; _effect.Parameters["xWorld"].SetValue(value); _world = value; } Thanking you in anticipation

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  • Generalized Ajax function [migrated]

    - by TecBrat
    Not sure if this question will be considered "off topic". If it is, I'll remove it, but: I hadn't see this yet so I wrote it and would like to know if this is a good approach to it. Would anyone care to offer improvements to it, or point me to an example of where someone else has already written it better? function clwAjaxCall(path,method,data,asynch) { var xmlhttp; if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp=new XMLHttpRequest(); } else {// code for IE6, IE5 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } if(asynch) { xmlhttp.onreadystatechange=function() { if (xmlhttp.readyState==4 && xmlhttp.status==200) { //alert(xmlhttp.responseText); //var newaction=xmlhttp.responseText; //alert('Action becomes '+newaction); return xmlhttp.responseText; } } } if(method=='GET'){path=path+"/?"+data;} xmlhttp.open(method,path,asynch); if(method=='GET'){xmlhttp.send();}else{xmlhttp.send(data);} if (!asynch){return xmlhttp.responseText;} } I then called it like Just Testing <script type="text/javascript" src="/mypath/js/clwAjaxCall.js"></script> <script type="text/javascript"> document.write("<br>More Testing"); document.write(clwAjaxCall("http://www.mysite.com",'GET',"var=val",false)); </script>

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  • Fog shader camera problem

    - by MaT
    I have some difficulties with my vertex-fragment fog shader in Unity. I have a good visual result but the problem is that the gradient is based on the camera's position, it moves as the camera moves. I don't know how to fix it. Here is the shader code. struct v2f { float4 pos : SV_POSITION; float4 grabUV : TEXCOORD0; float2 uv_depth : TEXCOORD1; float4 interpolatedRay : TEXCOORD2; float4 screenPos : TEXCOORD3; }; v2f vert(appdata_base v) { v2f o; o.pos = mul(UNITY_MATRIX_MVP, v.vertex); o.uv_depth = v.texcoord.xy; o.grabUV = ComputeGrabScreenPos(o.pos); half index = v.vertex.z; o.screenPos = ComputeScreenPos(o.pos); o.interpolatedRay = mul(UNITY_MATRIX_MV, v.vertex); return o; } sampler2D _GrabTexture; float4 frag(v2f IN) : COLOR { float3 uv = UNITY_PROJ_COORD(IN.grabUV); float dpth = UNITY_SAMPLE_DEPTH(tex2Dproj(_CameraDepthTexture, uv)); dpth = LinearEyeDepth(dpth); float4 wsPos = (IN.screenPos + dpth * IN.interpolatedRay); // Here is the problem but how to fix it float fogVert = max(0.0, (wsPos.y - _Depth) * (_DepthScale * 0.1f)); fogVert *= fogVert; fogVert = (exp (-fogVert)); return fogVert; } Thanks a lot !

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  • Image with FadeIn effect blinks when added to scene

    - by Ef Es
    I am trying to add an image to the scene, but it should just be added to the scene invisible, FadeIn and then be deleted when the effect finishes. My problem is that the images blink once when they are added to the scene, then they do the intended effect. My best guess is that when they are added they show on the scene for a split second before starting the animation. I though of making them invisible for a split second before activating them, but I am not sure how to code it. const bool Sunbeams::add() { const CCSize kSceenSize = CCDirector::sharedDirector()->getWinSize(); const int nRayType = random( m_kRays.size()); const CCPoint kPosition( random( static_cast < int >( kSceenSize.width)), 0.0f); const float fDuration = random( m_fDurationVariance) + m_fDurationMin; CCSprite* pkLightBeam = CCSprite::spriteWithTexture( m_kRays[nRayType]); if ( !pkLightBeam) { msg::debug( "Sunbeams::add", "Failed to create sprite from ray '%d'!\n", m_kRays[nRayType]); return false; } pkLightBeam->setAnchorPoint( CCPointZero); pkLightBeam->setPosition( kPosition); m_kActiveBeams.push_back( pkLightBeam); CCDirector::sharedDirector()->getRunningScene()->addChild( pkLightBeam); CCActionInterval* pkAction = CCFadeIn::actionWithDuration( fDuration); CCActionInterval* pkActionBack = pkAction->reverse(); pkLightBeam->runAction( CCSequence::actions( pkAction, pkActionBack, 0)); return true; }

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  • Creating Custom validation rule and register it

    - by FormsEleven
    What is Validation Rule? A validation rule is a piece of code that performs some check ensuring that data meets given constraints.In an enterprise application development environment, often it might require developers to have validation be performed based on some logic at several places across projects. Instead of redundant validation creation, a custom validation rule provides a library with a validation rules that can be registered and used across applications.A custom Validation is encapsulated in a reusable component so that you do not have to write it every time when you need to do input validation. Here is how we can easily implement a custom validation that checks for name of an employee to be "KING" For creating a custom Validation , 1.         Create Generic Application Workspace "CustomValidator" with the project "Model" 2.         Create an BC4J based on emp table. 3.         Create a custom validation rule.In EmpNamerule class, update the validateValue(..) method as follows:  public boolean validateValue(Object value) { EntityImpl emp = (EntityImpl)value; if(emp.getAttribute("Ename").toString().equals("KING")){ return false; } return true; } Create ADF Library: Next step would be to create ADF library. Create ADF library with name lets say testADFLibrary1.jarRegister ADF Library Next step is to register the ADF library , so that its available across the applications. Invoke the menu "Tools -> Preferences"Select the option "Business Components -> Registered Rules" from left paneClick on button "Pick Library". The dialog "Select Library" comes up with  the user library addedAdd new library' that points to the above jarCheck the checkbox "Register" and set the name for the rule Sample UsageHere is how we can easily implement a validation rule that restrict the name of the employee not to be "KING".Create new Application with BC4J based on EMP table.Create new validation under Business rule tab for Ename & select the above custom validation rule.Run the AppModule tester.

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  • Context Sensitive JTable

    - by Geertjan
    Here's a plain old JTable on the NetBeans Platform. Whenever the toolbar button is clicked, information about the currently selected row is displayed in the status bar: Normally, the above would be achieved in NetBeans Platform applications via Nodes publishing their underlying business object when the selection changes. In this case, there are no Nodes at all. There's only a JTable and a DefaultTableModel, i.e., all pure Java Swing. So, how does it work? To follow the logic, it makes sense to create the example yourself, starting with the Stock object: public class Stock {     String name;     String desc;     public Stock() {     }     public Stock(String name, String desc) {         this.name = name;         this.desc = desc;     }     public String getDesc() {         return desc;     }     public String getName() {         return name;     }     public void setDesc(String desc) {         this.desc = desc;     }     public void setName(String name) {         this.name = name;     } } Next, create a new Window Component via the wizard and then rewrite the constructor as follows: public final class MyWindowTopComponent extends TopComponent {     private final InstanceContent ic = new InstanceContent();     public MyWindowTopComponent() {         initComponents();         //Statically create a few stocks,         //in reality these would come from a data source         //of some kind:         List<Stock> list = new ArrayList();         list.add(new Stock("AMZN", "Amazon"));         list.add(new Stock("BOUT", "About.com"));         list.add(new Stock("Something", "Something.com"));         //Create a JTable, passing the List above         //to a DefaultTableModel:         final JTable table = new JTable(StockTableModel (list));         //Whenever the mouse is clicked on the table,         //somehow construct a new Stock object //(or get it from the List above) and publish it:         table.addMouseListener(new MouseAdapter() {             @Override             public void mousePressed(MouseEvent e) {                 int selectedColumn = table.getSelectedColumn();                 int selectedRow = table.getSelectedRow();                 Stock s = new Stock();                 if (selectedColumn == 0) {                     s.setName(table.getModel().getValueAt(selectedRow, 0).toString());                     s.setDesc(table.getModel().getValueAt(selectedRow, 1).toString());                 } else {                     s.setName(table.getModel().getValueAt(selectedRow, 1).toString());                     s.setDesc(table.getModel().getValueAt(selectedRow, 0).toString());                 }                 ic.set(Collections.singleton(s), null);             }         });         JScrollPane scrollPane = new JScrollPane(table);         add(scrollPane, BorderLayout.CENTER);         //Put the dynamic InstanceContent into the Lookup:         associateLookup(new AbstractLookup(ic));     }     private DefaultTableModel StockTableModel (List<Stock> stockList) {         DefaultTableModel stockTableModel = new DefaultTableModel() {             @Override             public boolean isCellEditable(int row, int column) {                 return false;             }         };         Object[] columnNames = new Object[2];         columnNames[0] = "Symbol";         columnNames[1] = "Name";         stockTableModel.setColumnIdentifiers(columnNames);         Object[] rows = new Object[2];         ListIterator<Stock> stockListIterator = stockList.listIterator();         while (stockListIterator.hasNext()) {             Stock nextStock = stockListIterator.next();             rows[0] = nextStock.getName();             rows[1] = nextStock.getDesc();             stockTableModel.addRow(rows);         }         return stockTableModel;     }     ...     ...     ... And now, since you're publishing a new Stock object whenever the user clicks in the table, you can create loosely coupled Actions, like this: @ActionID(category = "Edit", id = "org.my.ui.ShowStockAction") @ActionRegistration(iconBase = "org/my/ui/Datasource.gif", displayName = "#CTL_ShowStockAction") @ActionReferences({     @ActionReference(path = "Menu/File", position = 1300),     @ActionReference(path = "Toolbars/File", position = 300) }) @Messages("CTL_ShowStockAction=Show Stock") public final class ShowStockAction implements ActionListener {     private final Stock context;     public ShowStockAction(Stock context) {         this.context = context;     }     @Override     public void actionPerformed(ActionEvent ev) {         StatusDisplayer.getDefault().setStatusText(context.getName() + " / " + context.getDesc());     } }

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  • Using Shader causes triangle to disappear

    - by invisal
    The following is my rendering code. Private Sub GameRender() GL.Clear(ClearBufferMask.ColorBufferBit + ClearBufferMask.DepthBufferBit) GL.ClearColor(Color.SkyBlue) GL.UseProgram(theProgram) GL.EnableClientState(ArrayCap.VertexArray) GL.EnableClientState(ArrayCap.ColorArray) GL.BindBuffer(BufferTarget.ArrayBuffer, vertexPositionID) GL.DrawArrays(BeginMode.Triangles, 0, 3) GL.DisableClientState(ArrayCap.ColorArray) GL.DisableClientState(ArrayCap.VertexArray) GlControl1.SwapBuffers() End Sub This is screenshot without GL.UseProgram(theProgram) This is screenshot with GL.UseProgram(theProgram) Here are my shader code that I picked from online tutorial. Vertex Shader #version 330 layout(location = 0) in vec4 position; void main() { gl_Position = position; } Fragment Shader #version 330 out vec4 outputColor; void main() { outputColor = vec4(1.0f, 1.0f, 1.0f, 1.0f); } These are my shader creation code. '' Initialize Shader Dim shaderList(1) As Integer shaderList(0) = CreateShader(ShaderType.VertexShader, strVertexShader) shaderList(1) = CreateShader(ShaderType.FragmentShader, strFragShader) theProgram = CreateProgram(shaderList) GL.DeleteShader(shaderList(0)) GL.DeleteShader(shaderList(1)) Here are my helper functions Private Function CreateShader(ByVal shaderType As ShaderType, ByVal code As String) Dim shader As Integer = GL.CreateShader(shaderType) GL.ShaderSource(shader, code) GL.CompileShader(shader) Dim status As Integer GL.GetShader(shader, ShaderParameter.CompileStatus, status) If status = False Then MsgBox(GL.GetShaderInfoLog(shader)) End If Return shader End Function Private Function CreateProgram(ByVal shaderList() As Integer) As Integer Dim program As Integer = GL.CreateProgram() For i As Integer = 0 To shaderList.Length - 1 GL.AttachShader(program, shaderList(i)) Next GL.LinkProgram(program) Dim status As Integer GL.GetProgram(program, ProgramParameter.LinkStatus, status) If status = False Then MsgBox(GL.GetProgramInfoLog(program)) End If For i As Integer = 0 To shaderList.Length - 1 GL.DetachShader(program, shaderList(i)) Next Return program End Function

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  • What could cause a pixel shader to paint outside the lines of the vertex shader output?

    - by Rei Miyasaka
    From what I understand, the pixels that a pixel shader operates on are specified implicitly by the SV_POSITION output (in DirectX) of the vertex shader. What then could cause a pixel shader to render in the middle of nowhere? I used the new Visual Studio 2012 graphics debugger to visualize my vertex and pixel shader output. This is the output from a DrawIndexed() call that draws a cube: The pink part is the rendered output of the pixel shader, which takes the cube on its left as its input. The vertex shader code: cbuffer Buf { float4x4 final; }; struct In { float4 pos:POSITION; float3 norm:NORMAL; float2 texuv:TEXCOORD; }; struct Out { float4 col:COLOR; float2 tex:TEXCOORD; float4 pos:SV_POSITION; }; Out main(In input) { Out output; output.pos = mul(input.pos, final); output.col = float4(1.0f, 0.5f, 0.5f, 1.0f); output.tex = input.texuv; return output; } And the pixel shader: struct In { float4 col:COLOR; float2 tex:TEXCOORD; float4 pos:SV_POSITION; }; float4 main(In input) : SV_TARGET { return input.col; } The raster stage is the only thing between the vertex shader and the pixel shader, so my suspicion is that it's some raster stage settings. But the raster stage shouldn't change the shape of the vertex shader output so drastically, should it?

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  • PLINQ Adventure Land - WaitForAll

    - by adweigert
    PLINQ is awesome for getting a lot of work done fast, but one thing I haven't figured out yet is how to start work with PLINQ but only let it execute for a maximum amount of time and react if it is taking too long. So, as I must admit I am still learning PLINQ, I created this extension in that ignorance. It behaves similar to ForAll<> but takes a timeout and returns false if the threads don't complete in the specified amount of time. Hope this helps someone else take PLINQ further, it definitely has helped for me ...  public static bool WaitForAll<T>(this ParallelQuery<T> query, TimeSpan timeout, Action<T> action) { Contract.Requires(query != null); Contract.Requires(action != null); var exception = (Exception)null; var cts = new CancellationTokenSource(); var forAllWithCancellation = new Action(delegate { try { query.WithCancellation(cts.Token).ForAll(action); } catch (OperationCanceledException) { // NOOP } catch (AggregateException ex) { exception = ex; } }); var mrs = new ManualResetEvent(false); var callback = new AsyncCallback(delegate { mrs.Set(); }); var result = forAllWithCancellation.BeginInvoke(callback, null); if (mrs.WaitOne(timeout)) { forAllWithCancellation.EndInvoke(result); if (exception != null) { throw exception; } return true; } else { cts.Cancel(); return false; } }

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  • Update the model on HttpPost and render the changes in the View

    - by Etienne Giust
    With MVC3, I came over that problem where I was rendering a view with an updated model at the end of an HttpPost and the changes to the model were never applied to the rendered view :   NOT working as expected ! [HttpPost]         public ActionResult Edit(JobModel editedJobModel)         {             // Update some model property             editedJobModel.IsActive = true;                          // The view will NOT be updated as expected             return View(editedJobModel);         }   This is the standard behavior. In MVC3, POSTing the model does not render the Html helpers again. In my example, a HiddenFor bound to the IsActive value will not have its value set to true after the view is rendered.   Are you stuck, then ?   Well, for one, you’re not supposed to do that: in an ideal world you are supposed to apply the Post/Redirect/Get pattern. You would redirect to a new GET after your POST performed its actions. That’s what I usually do, but sometimes, when maintaining code and implementing slight changes to a pre-existing and tested logic, one prefers to keep structural changes to a minimum.   If you really have to (but my advice is to try to implement the PRG pattern whenever possible), here is a solution to alter values of the model on a POST and have the MVC engine render it correctly :   Solution [HttpPost] public ActionResult Edit(JobModel editedJobModel) {     // NOT WORKING : Update some model property     //editedJobModel.IsActive = true;     //Force ModelState value for IsActive property     ModelState["IsActive"].Value = new ValueProviderResult(true, "True", null);          // The view will be updated as expected     return View(editedJobModel); }   As you can see, it is a “dirty” solution, as the name (as a  string) of the updated property is used as a key of the ModelState dictionary. Also, the use of ValueProviderResult is not that straightforward.   But hey, it works.

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  • Force Blank TextBox with ASP.Net MVC Html.TextBox

    - by Doug Lampe
    I recently ran into a problem with the following scenario: I have data with a parent/child data with a one-to-many relationship from the parent to the child. I want to be able to update parent and existing child data AND add a new child record all in a single post. I don't want to create a model just to store the new values. One of the things I LOVE about MVC is how flexible it is in dealing with posted data.  If you have data that isn't in your model, you can simply use the non-strongly-typed HTML helper extensions and pass the data into your actions as parameters or use the FormCollection.  I thought this would give me the solution I was looking for.  I simply used Html.TextBox("NewChildKey") and Html.TextBox("NewChildValue") and added parameters to my action to take the new values.  So here is what my action looked like: [HttpPost] public ActionResult EditParent(int? id, string newChildKey, string newChildValue, FormCollection forms) {     Model model = ModelDataHelper.GetModel(id ?? 0);     if (model != null)     {         if (TryUpdateModel(model))         {             if (ModelState.IsValid)             {                 model = ModelDataHelper.UpdateModel(model);             }             string[] keys = forms.GetValues("ChildKey");             string[] values = forms.GetValues("ChildValue");             ModelDataHelper.UpdateChildData(id ?? 0, keys, values);             ModelDataHelper.AddChildData(id ?? 0, newChildKey, newChildValue);             model = ModelDataHelper.GetModel(id ?? 0);         }        return View(report);     }    return new EmptyResult(); } The only problem with this is that MVC is TOO smart.  Even though I am not using a model to store the new child values, MVC still passes the values back to the text boxes via the model state.  The fix for this is simple but not necessarily obvious, simply remove the data from the model state before returning the view: ModelState.Remove("NewChildKey"); ModelState.Remove("NewChildValue"); Two lines of code to save a lot of headaches.

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  • Restrict Tile Map to its boundaries

    - by Farooq Arshed
    I have loaded a tmx file in cocos2dx and now I am trying to implement panning. I have successfully implemented the panning first part where the map moves. Now I want to restrict the map so it does not display the map beyond its boundary where it shows black screen. I am confused as to how to implement it. Below is my code any help would be appreciated. bool HelloWorld::init() { if ( !CCLayer::init() ) { return false; } const char* tmx= "isometric_grass_and_water.tmx"; _tileMap = new CCTMXTiledMap(); _tileMap->initWithTMXFile(tmx); this->addChild(_tileMap); this->setTouchEnabled(true); return true; } void HelloWorld::ccTouchesBegan(CCSet *touches, CCEvent *event){ CCSetIterator it; for (it=touches->begin(); it!=touches->end(); ++it){ CCTouch* touch = (CCTouch*)it.operator*(); CCLog("touches id: %d", touch->getID()); oldLoc = touch->getLocationInView(); oldLoc = CCDirector::sharedDirector()->convertToGL(oldLoc); } } void HelloWorld::ccTouchesMoved(CCSet *touches, CCEvent *event) { if (touches->count() == 1) { CCTouch* touch = (CCTouch*)( touches->anyObject() ); this->moveScreen(touch); } else if (touches->count() == 2) { this->scaleScreen(touches); } } void HelloWorld::moveScreen(CCTouch* touch) { CCPoint currentLoc = touch->getLocationInView(); currentLoc = CCDirector::sharedDirector()->convertToGL(currentLoc); CCPoint moveTo = ccpSub(oldLoc, currentLoc); moveTo = ccpMult(moveTo, -1); oldLoc = currentLoc; this->setPosition(ccpAdd(this->getPosition(), ccp(moveTo.x, moveTo.y))); }

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  • When to use http status code 404

    - by Sybiam
    I am working on a project and after arguing with people at work for about more than a hour. I decided to know what people on stack-exchange might say. We're writing an API for a system, there is a query that should return a tree of Organization or a tree of Goals. The tree of Organization is the organization in which the user is present, In other words, this tree should always exists. In the organization, a tree of goal should be always present. (that's where the argument started). In case where the tree doesn't exist, my co-worker decided that it would be right to answer response with status code 200. And then started asking me to fix my code because the application was falling apart when there is no tree. I'll try to spare flames and fury. I suggested to raise a 404 error when there is no tree. It would at least let me know that something is wrong. When using 200, I have to add special check to my response in the success callback to handle errors. I'm expecting to receive an object, but I may actually receive an empty response because nothing is found. It sounds totally fair to mark the response as a 404. And then war started and I got the message that I didn't understand HTTP status code schema. So I'm here and asking what's wrong with 404 in this case? I even got the argument "It found nothing, so it's right to return 200". I believe that it's wrong since the tree should be always present. If we found nothing and we are expecting something, it should be a 404. Extra Also, I believe the best answer to the problem is to create default objects when organizations are created, having no tree shouldn't be a valid case and should be seen as an undefined behavior. There is no way an account can be used without both trees. For that reasons, they should be always present.

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  • Maintaining State in Mud Engine

    - by Johnathon Sullinger
    I am currently working on a Mud Engine and have started implementing my state engine. One of the things that has me troubled is maintaining different states at once. For instance, lets say that the user has started a tutorial, which requires specific input. If the user types "help" I want to switch in to a help state, so they can get the help they need, then return them to the original state once exiting the help. my state system uses a State Manager to manage the state per user: public class StateManager { /// <summary> /// Gets the current state. /// </summary> public IState CurrentState { get; private set; } /// <summary> /// Gets the states available for use. /// </summary> /// <value> public List<IState> States { get; private set; } /// <summary> /// Gets the commands available. /// </summary> public List<ICommand> Commands { get; private set; } /// <summary> /// Gets the mob that this manager controls the state of. /// </summary> public IMob Mob { get; private set; } public void Initialize(IMob mob, IState initialState = null) { this.Mob = mob; if (initialState != null) { this.SwitchState(initialState); } } /// <summary> /// Performs the command. /// </summary> /// <param name="message">The message.</param> public void PerformCommand(IMessage message) { if (this.CurrentState != null) { ICommand command = this.CurrentState.GetCommand(message); if (command is NoOpCommand) { // NoOperation commands indicate that the current state is not finished yet. this.CurrentState.Render(this.Mob); } else if (command != null) { command.Execute(this.Mob); } else if (command == null) { new InvalidCommand().Execute(this.Mob); } } } /// <summary> /// Switches the state. /// </summary> /// <param name="state">The state.</param> public void SwitchState(IState state) { if (this.CurrentState != null) { this.CurrentState.Cleanup(); } this.CurrentState = state; if (state != null) { this.CurrentState.Render(this.Mob); } } } Each of the different states that the user can be in, is a Type implementing IState. public interface IState { /// <summary> /// Renders the current state to the players terminal. /// </summary> /// <param name="player">The player to render to</param> void Render(IMob mob); /// <summary> /// Gets the Command that the player entered and preps it for execution. /// </summary> /// <returns></returns> ICommand GetCommand(IMessage command); /// <summary> /// Cleanups this instance during a state change. /// </summary> void Cleanup(); } Example state: public class ConnectState : IState { /// <summary> /// The connected player /// </summary> private IMob connectedPlayer; public void Render(IMob mob) { if (!(mob is IPlayer)) { throw new NullReferenceException("ConnectState can only be used with a player object implementing IPlayer"); } //Store a reference for the GetCommand() method to use. this.connectedPlayer = mob as IPlayer; var server = mob.Game as IServer; var game = mob.Game as IGame; // It is not guaranteed that mob.Game will implement IServer. We are only guaranteed that it will implement IGame. if (server == null) { throw new NullReferenceException("LoginState can only be set to a player object that is part of a server."); } //Output the game information mob.Send(new InformationalMessage(game.Name)); mob.Send(new InformationalMessage(game.Description)); mob.Send(new InformationalMessage(string.Empty)); //blank line //Output the server MOTD information mob.Send(new InformationalMessage(string.Join("\n", server.MessageOfTheDay))); mob.Send(new InformationalMessage(string.Empty)); //blank line mob.StateManager.SwitchState(new LoginState()); } /// <summary> /// Gets the command. /// </summary> /// <param name="message">The message.</param> /// <returns>Returns no operation required.</returns> public Commands.ICommand GetCommand(IMessage message) { return new NoOpCommand(); } /// <summary> /// Cleanups this instance during a state change. /// </summary> public void Cleanup() { // We have nothing to clean up. return; } } With the way that I have my FSM set up at the moment, the user can only ever have one state at a time. I read a few different posts on here about state management but nothing regarding keeping a stack history. I thought about using a Stack collection, and just pushing new states on to the stack then popping them off as the user moves out from one. It seems like it would work, but I'm not sure if it is the best approach to take. I'm looking for recommendations on this. I'm currently swapping state from within the individual states themselves as well which I'm on the fence about if it makes sense to do there or not. The user enters a command, the StateManager passes the command to the current State and lets it determine if it needs it (like passing in a password after entering a user name), if the state doesn't need any further commands, it returns null. If it does need to continue doing work, it returns a No Operation to let the state manager know that the state still requires further input from the user. If null is returned, the state manager will then go find the appropriate state for the command entered by the user. Example state requiring additional input from the user public class LoginState : IState { /// <summary> /// The connected player /// </summary> private IPlayer connectedPlayer; private enum CurrentState { FetchUserName, FetchPassword, InvalidUser, } private CurrentState currentState; /// <summary> /// Renders the current state to the players terminal. /// </summary> /// <param name="mob"></param> /// <exception cref="System.NullReferenceException"> /// ConnectState can only be used with a player object implementing IPlayer /// or /// LoginState can only be set to a player object that is part of a server. /// </exception> public void Render(IMob mob) { if (!(mob is IPlayer)) { throw new NullReferenceException("ConnectState can only be used with a player object implementing IPlayer"); } //Store a reference for the GetCommand() method to use. this.connectedPlayer = mob as IPlayer; var server = mob.Game as IServer; // Register to receive new input from the user. mob.ReceivedMessage += connectedPlayer_ReceivedMessage; if (server == null) { throw new NullReferenceException("LoginState can only be set to a player object that is part of a server."); } this.currentState = CurrentState.FetchUserName; switch (this.currentState) { case CurrentState.FetchUserName: mob.Send(new InputMessage("Please enter your user name")); break; case CurrentState.FetchPassword: mob.Send(new InputMessage("Please enter your password")); break; case CurrentState.InvalidUser: mob.Send(new InformationalMessage("Invalid username/password specified.")); this.currentState = CurrentState.FetchUserName; mob.Send(new InputMessage("Please enter your user name")); break; } } /// <summary> /// Receives the players input. /// </summary> /// <param name="sender">The sender.</param> /// <param name="e">The e.</param> void connectedPlayer_ReceivedMessage(object sender, IMessage e) { // Be good memory citizens and clean ourself up after receiving a message. // Not doing this results in duplicate events being registered and memory leaks. this.connectedPlayer.ReceivedMessage -= connectedPlayer_ReceivedMessage; ICommand command = this.GetCommand(e); } /// <summary> /// Gets the Command that the player entered and preps it for execution. /// </summary> /// <param name="command"></param> /// <returns>Returns the ICommand specified.</returns> public Commands.ICommand GetCommand(IMessage command) { if (this.currentState == CurrentState.FetchUserName) { this.connectedPlayer.Name = command.Message; this.currentState = CurrentState.FetchPassword; } else if (this.currentState == CurrentState.FetchPassword) { // find user } return new NoOpCommand(); } /// <summary> /// Cleanups this instance during a state change. /// </summary> public void Cleanup() { // If we have a player instance, we clean up the registered event. if (this.connectedPlayer != null) { this.connectedPlayer.ReceivedMessage -= this.connectedPlayer_ReceivedMessage; } } Maybe my entire FSM isn't wired up in the best way, but I would appreciate input on what would be the best to maintain a stack of state in a MUD game engine, and if my states should be allowed to receive the input from the user or not to check what command was entered before allowing the state manager to switch states. Thanks in advance.

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  • Updating physics for animated models

    - by Mathias Hölzl
    For a new game we have do set up a scene with a minimum of 30 bone animated models.(shooter) The problem is that the update process for the animated models takes too long. Thats what I do: Each character has ~30 bones and for every update tick the animation gets calculated and every bone fires a event with the new matrix. The physics receives the event with the new matrix and updates the collision shape for that bone. The time that it takes to build the animation isn't that bad (0.2ms for 30 Bones - 6ms for 30 models). But the main problem is that the physic engine (Bullet) uses a diffrent matrix for transformation and so its necessary to convert it. Code for matrix conversion: (~0.005ms) btTransform CLEAR_PHYSICS_API Mat_to_btTransform( Mat mat ) { btMatrix3x3 bulletRotation; btVector3 bulletPosition; XMFLOAT4X4 matData = mat.GetStorage(); // copy rotation matrix for ( int row=0; row<3; ++row ) for ( int column=0; column<3; ++column ) bulletRotation[row][column] = matData.m[column][row]; for ( int column=0; column<3; ++column ) bulletPosition[column] = matData.m[3][column]; return btTransform( bulletRotation, bulletPosition ); } The function for updating the transform(Physic): void CLEAR_PHYSICS_API BulletPhysics::VKinematicMove(Mat mat, ActorId aid) { if ( btRigidBody * const body = FindActorBody( aid ) ) { btTransform tmp = Mat_to_btTransform( mat ); body->setWorldTransform( tmp ); } } The real problem is the function FindActorBody(id): ActorIDToBulletActorMap::const_iterator found = m_actorBodies.find( id ); if ( found != m_actorBodies.end() ) return found->second; All physic actors are stored in m_actorBodies and thats why the updating process takes to long. But I have no idea how I could avoid this. Friendly greedings, Mathias

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  • Switch vs Polymorphism when dealing with model and view

    - by Raphael Oliveira
    I can't figure out a better solution to my problem. I have a view controller that presents a list of elements. Those elements are models that can be an instance of B, C, D, etc and inherit from A. So in that view controller, each item should go to a different screen of the application and pass some data when the user select one of them. The two alternatives that comes to my mind are (please ignore the syntax, it is not a specific language) 1) switch (I know that sucks) //inside the view controller void onClickItem(int index) { A a = items.get(index); switch(a.type) { case b: B b = (B)a; go to screen X; x.v1 = b.v1; // fill X with b data x.v2 = b.v2; case c: go to screen Y; etc... } } 2) polymorphism //inside the view controller void onClickItem(int index) { A a = items.get(index); Screen s = new (a.getDestinationScreen()); //ignore the syntax s.v1 = a.v1; // fill s with information about A s.v2 = a.v2; show(s); } //inside B Class getDestinationScreen(void) { return Class(X); } //inside C Class getDestinationScreen(void) { return Class(Y); } My problem with solution 2 is that since B, C, D, etc are models, they shouldn't know about view related stuff. Or should they in that case?

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  • Quantifying the value of refactoring in commercial terms

    - by Myles McDonnell
    Here is the classic scenario; Dev team build a prototype. Business mgmt like it and put it into production. Dev team now have to continue to deliver new features whilst at the same time pay the technical debt accrued when the code base was a prototype. My question is this (forgive me, it's rather open ended); how can the value of the refactoring work be quantified in commercial terms? As developers we can clearly understand and communicate the value in technical terms, such a the removal of code duplication, the simplification of an object model and so on. But this means little to an executive focussed on the commercial elements. What will mean something to this executive is the dev. team being able to deliver requirements at faster velocity. Just making this statement without any metrics that clearly quantify return on investment (increased velocity in return for resource allocated to refactoring) carries little weight. I'm interested to hear from anyone who has had experience, positive or negative, in relation to the above. ----------------- EDIT ---------------- Thanks for the responses so far, all of which I think are good. What I want to develop is a metric that proves (or disproves!) all of these statements. A report that ties velocity to refactoring and shows a positive effect.

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  • Why unhandled exceptions are useful

    - by Simon Cooper
    It’s the bane of most programmers’ lives – an unhandled exception causes your application or webapp to crash, an ugly dialog gets displayed to the user, and they come complaining to you. Then, somehow, you need to figure out what went wrong. Hopefully, you’ve got a log file, or some other way of reporting unhandled exceptions (obligatory employer plug: SmartAssembly reports an application’s unhandled exceptions straight to you, along with the entire state of the stack and variables at that point). If not, you have to try and replicate it yourself, or do some psychic debugging to try and figure out what’s wrong. However, it’s good that the program crashed. Or, more precisely, it is correct behaviour. An unhandled exception in your application means that, somewhere in your code, there is an assumption that you made that is actually invalid. Coding assumptions Let me explain a bit more. Every method, every line of code you write, depends on implicit assumptions that you have made. Take this following simple method, that copies a collection to an array and includes an item if it isn’t in the collection already, using a supplied IEqualityComparer: public static T[] ToArrayWithItem( ICollection<T> coll, T obj, IEqualityComparer<T> comparer) { // check if the object is in collection already // using the supplied comparer foreach (var item in coll) { if (comparer.Equals(item, obj)) { // it's in the collection already // simply copy the collection to an array // and return it T[] array = new T[coll.Count]; coll.CopyTo(array, 0); return array; } } // not in the collection // copy coll to an array, and add obj to it // then return it T[] array = new T[coll.Count+1]; coll.CopyTo(array, 0); array[array.Length-1] = obj; return array; } What’s all the assumptions made by this fairly simple bit of code? coll is never null comparer is never null coll.CopyTo(array, 0) will copy all the items in the collection into the array, in the order defined for the collection, starting at the first item in the array. The enumerator for coll returns all the items in the collection, in the order defined for the collection comparer.Equals returns true if the items are equal (for whatever definition of ‘equal’ the comparer uses), false otherwise comparer.Equals, coll.CopyTo, and the coll enumerator will never throw an exception or hang for any possible input and any possible values of T coll will have less than 4 billion items in it (this is a built-in limit of the CLR) array won’t be more than 2GB, both on 32 and 64-bit systems, for any possible values of T (again, a limit of the CLR) There are no threads that will modify coll while this method is running and, more esoterically: The C# compiler will compile this code to IL according to the C# specification The CLR and JIT compiler will produce machine code to execute the IL on the user’s computer The computer will execute the machine code correctly That’s a lot of assumptions. Now, it could be that all these assumptions are valid for the situations this method is called. But if this does crash out with an exception, or crash later on, then that shows one of the assumptions has been invalidated somehow. An unhandled exception shows that your code is running in a situation which you did not anticipate, and there is something about how your code runs that you do not understand. Debugging the problem is the process of learning more about the new situation and how your code interacts with it. When you understand the problem, the solution is (usually) obvious. The solution may be a one-line fix, the rewrite of a method or class, or a large-scale refactoring of the codebase, but whatever it is, the fix for the crash will incorporate the new information you’ve gained about your own code, along with the modified assumptions. When code is running with an assumption or invariant it depended on broken, then the result is ‘undefined behaviour’. Anything can happen, up to and including formatting the entire disk or making the user’s computer sentient and start doing a good impression of Skynet. You might think that those can’t happen, but at Halting problem levels of generality, as soon as an assumption the code depended on is broken, the program can do anything. That is why it’s important to fail-fast and stop the program as soon as an invariant is broken, to minimise the damage that is done. What does this mean in practice? To start with, document and check your assumptions. As with most things, there is a level of judgement required. How you check and document your assumptions depends on how the code is used (that’s some more assumptions you’ve made), how likely it is a method will be passed invalid arguments or called in an invalid state, how likely it is the assumptions will be broken, how expensive it is to check the assumptions, and how bad things are likely to get if the assumptions are broken. Now, some assumptions you can assume unless proven otherwise. You can safely assume the C# compiler, CLR, and computer all run the method correctly, unless you have evidence of a compiler, CLR or processor bug. You can also assume that interface implementations work the way you expect them to; implementing an interface is more than simply declaring methods with certain signatures in your type. The behaviour of those methods, and how they work, is part of the interface contract as well. For example, for members of a public API, it is very important to document your assumptions and check your state before running the bulk of the method, throwing ArgumentException, ArgumentNullException, InvalidOperationException, or another exception type as appropriate if the input or state is wrong. For internal and private methods, it is less important. If a private method expects collection items in a certain order, then you don’t necessarily need to explicitly check it in code, but you can add comments or documentation specifying what state you expect the collection to be in at a certain point. That way, anyone debugging your code can immediately see what’s wrong if this does ever become an issue. You can also use DEBUG preprocessor blocks and Debug.Assert to document and check your assumptions without incurring a performance hit in release builds. On my coding soapbox… A few pet peeves of mine around assumptions. Firstly, catch-all try blocks: try { ... } catch { } A catch-all hides exceptions generated by broken assumptions, and lets the program carry on in an unknown state. Later, an exception is likely to be generated due to further broken assumptions due to the unknown state, causing difficulties when debugging as the catch-all has hidden the original problem. It’s much better to let the program crash straight away, so you know where the problem is. You should only use a catch-all if you are sure that any exception generated in the try block is safe to ignore. That’s a pretty big ask! Secondly, using as when you should be casting. Doing this: (obj as IFoo).Method(); or this: IFoo foo = obj as IFoo; ... foo.Method(); when you should be doing this: ((IFoo)obj).Method(); or this: IFoo foo = (IFoo)obj; ... foo.Method(); There’s an assumption here that obj will always implement IFoo. If it doesn’t, then by using as instead of a cast you’ve turned an obvious InvalidCastException at the point of the cast that will probably tell you what type obj actually is, into a non-obvious NullReferenceException at some later point that gives you no information at all. If you believe obj is always an IFoo, then say so in code! Let it fail-fast if not, then it’s far easier to figure out what’s wrong. Thirdly, document your assumptions. If an algorithm depends on a non-trivial relationship between several objects or variables, then say so. A single-line comment will do. Don’t leave it up to whoever’s debugging your code after you to figure it out. Conclusion It’s better to crash out and fail-fast when an assumption is broken. If it doesn’t, then there’s likely to be further crashes along the way that hide the original problem. Or, even worse, your program will be running in an undefined state, where anything can happen. Unhandled exceptions aren’t good per-se, but they give you some very useful information about your code that you didn’t know before. And that can only be a good thing.

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