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  • C#: Handling Notifications: inheritance, events, or delegates?

    - by James Michael Hare
    Often times as developers we have to design a class where we get notification when certain things happen. In older object-oriented code this would often be implemented by overriding methods -- with events, delegates, and interfaces, however, we have far more elegant options. So, when should you use each of these methods and what are their strengths and weaknesses? Now, for the purposes of this article when I say notification, I'm just talking about ways for a class to let a user know that something has occurred. This can be through any programmatic means such as inheritance, events, delegates, etc. So let's build some context. I'm sitting here thinking about a provider neutral messaging layer for the place I work, and I got to the point where I needed to design the message subscriber which will receive messages from the message bus. Basically, what we want is to be able to create a message listener and have it be called whenever a new message arrives. Now, back before the flood we would have done this via inheritance and an abstract class: 1:  2: // using inheritance - omitting argument null checks and halt logic 3: public abstract class MessageListener 4: { 5: private ISubscriber _subscriber; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber) 11: { 12: _subscriber = subscriber; 13: _messageThread = new Thread(MessageLoop); 14: _messageThread.Start(); 15: } 16:  17: // user will override this to process their messages 18: protected abstract void OnMessageReceived(Message msg); 19:  20: // handle the looping in the thread 21: private void MessageLoop() 22: { 23: while(!_isHalted) 24: { 25: // as long as processing, wait 1 second for message 26: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 27: if(msg != null) 28: { 29: OnMessageReceived(msg); 30: } 31: } 32: } 33: ... 34: } It seems so odd to write this kind of code now. Does it feel odd to you? Maybe it's just because I've gotten so used to delegation that I really don't like the feel of this. To me it is akin to saying that if I want to drive my car I need to derive a new instance of it just to put myself in the driver's seat. And yet, unquestionably, five years ago I would have probably written the code as you see above. To me, inheritance is a flawed approach for notifications due to several reasons: Inheritance is one of the HIGHEST forms of coupling. You can't seal the listener class because it depends on sub-classing to work. Because C# does not allow multiple-inheritance, I've spent my one inheritance implementing this class. Every time you need to listen to a bus, you have to derive a class which leads to lots of trivial sub-classes. The act of consuming a message should be a separate responsibility than the act of listening for a message (SRP). Inheritance is such a strong statement (this IS-A that) that it should only be used in building type hierarchies and not for overriding use-specific behaviors and notifications. Chances are, if a class needs to be inherited to be used, it most likely is not designed as well as it could be in today's modern programming languages. So lets look at the other tools available to us for getting notified instead. Here's a few other choices to consider. Have the listener expose a MessageReceived event. Have the listener accept a new IMessageHandler interface instance. Have the listener accept an Action<Message> delegate. Really, all of these are different forms of delegation. Now, .NET events are a bit heavier than the other types of delegates in terms of run-time execution, but they are a great way to allow others using your class to subscribe to your events: 1: // using event - ommiting argument null checks and halt logic 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private bool _isHalted = false; 6: private Thread _messageThread; 7:  8: // assign the subscriber and start the messaging loop 9: public MessageListener(ISubscriber subscriber) 10: { 11: _subscriber = subscriber; 12: _messageThread = new Thread(MessageLoop); 13: _messageThread.Start(); 14: } 15:  16: // user will override this to process their messages 17: public event Action<Message> MessageReceived; 18:  19: // handle the looping in the thread 20: private void MessageLoop() 21: { 22: while(!_isHalted) 23: { 24: // as long as processing, wait 1 second for message 25: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 26: if(msg != null && MessageReceived != null) 27: { 28: MessageReceived(msg); 29: } 30: } 31: } 32: } Note, now we can seal the class to avoid changes and the user just needs to provide a message handling method: 1: theListener.MessageReceived += CustomReceiveMethod; However, personally I don't think events hold up as well in this case because events are largely optional. To me, what is the point of a listener if you create one with no event listeners? So in my mind, use events when handling the notification is optional. So how about the delegation via interface? I personally like this method quite a bit. Basically what it does is similar to inheritance method mentioned first, but better because it makes it easy to split the part of the class that doesn't change (the base listener behavior) from the part that does change (the user-specified action after receiving a message). So assuming we had an interface like: 1: public interface IMessageHandler 2: { 3: void OnMessageReceived(Message receivedMessage); 4: } Our listener would look like this: 1: // using delegation via interface - omitting argument null checks and halt logic 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private IMessageHandler _handler; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber, IMessageHandler handler) 11: { 12: _subscriber = subscriber; 13: _handler = handler; 14: _messageThread = new Thread(MessageLoop); 15: _messageThread.Start(); 16: } 17:  18: // handle the looping in the thread 19: private void MessageLoop() 20: { 21: while(!_isHalted) 22: { 23: // as long as processing, wait 1 second for message 24: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 25: if(msg != null) 26: { 27: _handler.OnMessageReceived(msg); 28: } 29: } 30: } 31: } And they would call it by creating a class that implements IMessageHandler and pass that instance into the constructor of the listener. I like that this alleviates the issues of inheritance and essentially forces you to provide a handler (as opposed to events) on construction. Well, this is good, but personally I think we could go one step further. While I like this better than events or inheritance, it still forces you to implement a specific method name. What if that name collides? Furthermore if you have lots of these you end up either with large classes inheriting multiple interfaces to implement one method, or lots of small classes. Also, if you had one class that wanted to manage messages from two different subscribers differently, it wouldn't be able to because the interface can't be overloaded. This brings me to using delegates directly. In general, every time I think about creating an interface for something, and if that interface contains only one method, I start thinking a delegate is a better approach. Now, that said delegates don't accomplish everything an interface can. Obviously having the interface allows you to refer to the classes that implement the interface which can be very handy. In this case, though, really all you want is a method to handle the messages. So let's look at a method delegate: 1: // using delegation via delegate - omitting argument null checks and halt logic 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private Action<Message> _handler; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber, Action<Message> handler) 11: { 12: _subscriber = subscriber; 13: _handler = handler; 14: _messageThread = new Thread(MessageLoop); 15: _messageThread.Start(); 16: } 17:  18: // handle the looping in the thread 19: private void MessageLoop() 20: { 21: while(!_isHalted) 22: { 23: // as long as processing, wait 1 second for message 24: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 25: if(msg != null) 26: { 27: _handler(msg); 28: } 29: } 30: } 31: } Here the MessageListener now takes an Action<Message>.  For those of you unfamiliar with the pre-defined delegate types in .NET, that is a method with the signature: void SomeMethodName(Message). The great thing about delegates is it gives you a lot of power. You could create an anonymous delegate, a lambda, or specify any other method as long as it satisfies the Action<Message> signature. This way, you don't need to define an arbitrary helper class or name the method a specific thing. Incidentally, we could combine both the interface and delegate approach to allow maximum flexibility. Doing this, the user could either pass in a delegate, or specify a delegate interface: 1: // using delegation - give users choice of interface or delegate 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private Action<Message> _handler; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber, Action<Message> handler) 11: { 12: _subscriber = subscriber; 13: _handler = handler; 14: _messageThread = new Thread(MessageLoop); 15: _messageThread.Start(); 16: } 17:  18: // passes the interface method as a delegate using method group 19: public MessageListener(ISubscriber subscriber, IMessageHandler handler) 20: : this(subscriber, handler.OnMessageReceived) 21: { 22: } 23:  24: // handle the looping in the thread 25: private void MessageLoop() 26: { 27: while(!_isHalted) 28: { 29: // as long as processing, wait 1 second for message 30: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 31: if(msg != null) 32: { 33: _handler(msg); 34: } 35: } 36: } 37: } } This is the method I tend to prefer because it allows the user of the class to choose which method works best for them. You may be curious about the actual performance of these different methods. 1: Enter iterations: 2: 1000000 3:  4: Inheritance took 4 ms. 5: Events took 7 ms. 6: Interface delegation took 4 ms. 7: Lambda delegate took 5 ms. Before you get too caught up in the numbers, however, keep in mind that this is performance over over 1,000,000 iterations. Since they are all < 10 ms which boils down to fractions of a micro-second per iteration so really any of them are a fine choice performance wise. As such, I think the choice of what to do really boils down to what you're trying to do. Here's my guidelines: Inheritance should be used only when defining a collection of related types with implementation specific behaviors, it should not be used as a hook for users to add their own functionality. Events should be used when subscription is optional or multi-cast is desired. Interface delegation should be used when you wish to refer to implementing classes by the interface type or if the type requires several methods to be implemented. Delegate method delegation should be used when you only need to provide one method and do not need to refer to implementers by the interface name.

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  • problem to genrate swf file.

    - by nemade-vipin
    hello friend I have created one flex Air application where I have created the one authentication actionscript class. and one mxml file.This complete application using webservice and google map API. but when I am building application it is not genrating the SWF file in bin-debug folder. that is changes not reflecting in our application. my code is:- Action script class is :- package src { import adobe.utils.XMLUI; import mx.rpc.events.FaultEvent; import mx.controls.Alert; import generated.webservices.*; import mx.collections.ArrayCollection; public class Authentication { [Bindable] private var childName:ArrayCollection; [Bindable] private var childId:ArrayCollection; private var photoFeed:ArrayCollection; private var arrayOfchild:Array; private var newEntry:GetSBTSMobileAuthentication; public function authentication():void { // Instantiate a new Entry object. user = new SBTSWebService(); if(user!=null) { user.addSBTSWebServiceFaultEventListener(handleFaults); user.addgetSBTSMobileAuthenticationEventListener(authenticationResult); newEntry = new GetSBTSMobileAuthentication(); if(newEntry!=null) { newEntry.mobile=mobileno.text; newEntry.password=password.text; user.getSBTSMobileAuthentication(newEntry); } } } public function handleFaults(event:FaultEvent):void { Alert.show("A fault occured contacting the server. Fault message is: " + event.fault.faultString); } public function authenticationResult(event:GetSBTSMobileAuthenticationResultEvent):void { if(event.result != null && event.result._return>0) { if(event.result._return > 0) { var UserId:int = event.result._return; loginform.enabled = false; //getChildList(UserId); viewstack2.selectedIndex=1; } else { Alert.show("Authentication fail"); } } } } } mxml file is :- import src.Authentication; var user:Authentication = new Authentication(); ]]> <mx:TabNavigator id="viewstack2" selectedIndex="0" creationPolicy="all" width="100%" height="100%"> <mx:Form label="Login Form" id="loginform"> <mx:FormItem label="Mobile NO:"> <mx:TextInput id="mobileno"/> </mx:FormItem> <mx:FormItem label="Password:"> <mx:TextInput displayAsPassword="true" id="password" /> </mx:FormItem> <mx:FormItem> <mx:Button label="Login" click="user.authentication()"/> </mx:FormItem> </mx:Form> <mx:Form label="Child List"> <mx:Label width="100%" color="blue" text="Select Child."/> </mx:Form> <mx:Form label="Child Information"> </mx:Form> <mx:Form label="Bus Location"> </mx:Form> <mx:Form label="Bus path"> </mx:Form> </mx:TabNavigator> </mx:Panel>

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  • How to get HTTP status code in HTTPService fault handler

    - by Ankur
    I am calling a server method through HTTPService from client side. The server is a RestFul web service and it might respond with one of many HTTP error codes (say, 400 for one error, 404 for another and 409 for yet another). I have been trying to find out the way to determine what was the exact error code sent by the server. I have walked teh entire object tree for the FaultEvent populated in my fault handler, but no where does it tell me the error code. Is this missing functionality in Flex? My code looks like this: The HTTP Service declaration: <mx:HTTPService id="myServerCall" url="myService" method="GET" resultFormat="e4x" result="myServerCallCallBack(event)" fault="faultHandler(event)"> <mx:request> <action>myServerCall</action> <docId>{m_sDocId}</docId> </mx:request> </mx:HTTPService> My fault handler code is like so: private function faultHandler(event : FaultEvent):void { Alert.show(event.statusCode.toString() + " / " + event.fault.message.toString()); }

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  • c# binarysearch a list<T> by a member of T

    - by Pygmy
    I have a baseclass Event with a DateTime member TimeStamp. Lots of other event-classes will derive from this. I want to be able to search a list of events (that can contain events with duplicate timestamps) fast, so I'd like to use a binary search. So I started out writing something like this : public class EventList<T> : List<T> where T : Event { private IComparer<T> comparer = (x, y) => Comparer<DateTime>.Default.Compare(x.TimeStamp, y.TimeStamp); public IEnumerable<T> EventsBetween(DateTime inFromTime, DateTime inToTime) { // Find the index for the beginning. int index = this.BinarySearch(inFromTime, comparer); // BLAH REST OF IMPLEMENTATION } } The problem is that the BinarySearch only accepts T (so - an Event type) as parameter, while I want to search based on a member of T - the TimeStamp. What would be a good way to approach this ?

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  • Can't remove Enter_Frame and stop TimerEvent

    - by Hwang
    I wanted to remove an ENTER_FRAME object and stopping an TimerEvent when I click on a button, and rerun ENTER_FRAME and TimerEvent when I click on another button. I've tried removeAddEventListener and stop() for the time, but I won't work. Any idea whats the problem here? package{ import flash.display.MovieClip; import flash.display.DisplayObject; import flash.events.Event; import flash.events.TimerEvent; import flash.utils.Timer; public class clockFunction extends MovieClip { private var clock:clockMC=new clockMC(); private var countdownTimer:Timer; //seconds private var secTop1=clock.second.top1.digit; private var secTop2=clock.second.top2.digit; private var secBot1=clock.second.bot1.digit; private var secBot2=clock.second.bot2.digit; private var seconds:Number; private var minutes:Number; private var hours:Number; private var days:Number; public function clockFunction():void { decrease(); addChild(clock); } private function decrease():void { countdownTimer=new Timer(1000); //Adding an event listener to the timer object countdownTimer.addEventListener(TimerEvent.TIMER,updateTime); //Initializing timer object //countdownTimer.start(); } private function updateTime(event:TimerEvent):void { decreasTimerFunction(); clock.second.play(); if (seconds==1) { clock.minute.play(); } if ((minutes==1)&&(seconds==1)) { clock.hour.play(); } if ((hours==1)&&(minutes==1)&&(seconds==1)) { clock.day.play(); } } //Setting it back to its correct time so it won't have number changing in between of flipping issues. private function detect(event:Event):void { //seconds var sec1=seconds; var sec2=seconds-1; if (sec1<10) { sec1="0"+sec1; } if (sec2<10) { sec2="0"+sec2; } if (sec1==00) { sec2=59; } secTop1.text=sec1; secTop2.text=sec2; secBot1.text=sec1; secBot2.text=sec2; } public function startTime():void { addEventListener(Event.ENTER_FRAME,detect); countdownTimer.start(); trace("start"); } public function stopTime():void { countdownTimer.stop(); removeEventListener(Event.ENTER_FRAME,detect); trace("stop"); } private function decreasTimerFunction():void { //Create a date object for Christmas Morning var endTime:Date=new Date(2010,3,26,20,0,0); //Current date object var now:Date=new Date(); // Set the difference between the two date and times in milliseconds var timeDiff:Number=endTime.getTime()-now.getTime(); seconds=Math.floor(timeDiff/1000); minutes=Math.floor(seconds/60); hours=Math.floor(minutes/60); days=Math.floor(hours/24); // Set the remainder of the division vars above hours%=24; minutes%=60; seconds%=60; } } }

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  • Help me re-center a ModalPopup within an iframe when the iframe's parent window scrolls

    - by Cory Larson
    I have a web page with an iframe in it (I don't like it, but that's the way it has to be). It's not a cross-domain iframe so there's nothing to worry about there. I have written a jQuery extension that does the centering of a ModalPopup (which is called from an overridden AjaxControlToolkit.ModalPopupBehavior._layout method) based on the width and height of the iframe's parent, so that it looks centered even though the iframe is not in the center of the page. It's a lot of tricky stuff, especially since the web page I added the iframe to runs in quirks mode. Now, I've also overridden AjaxControlToolkit.ModalPopupBehavior._attachPopup, so that when the parent window resizes or scrolls, the ModalPopup inside of the iframe recenter's itself relative to the new size of the parent window. However, the same code that attaches the popup to the parent window's resize event does NOT work for the parent window's scroll event. See the code below, and the comments: AjaxControlToolkit.ModalPopupBehavior.prototype._attachPopup = function() { /// <summary> /// Attach the event handlers for the popup to the PARENT window /// </summary> if (this._DropShadow && !this._dropShadowBehavior) { this._dropShadowBehavior = $create(AjaxControlToolkit.DropShadowBehavior, {}, null, null, this._popupElement); } if (this._dragHandleElement && !this._dragBehavior) { this._dragBehavior = $create(AjaxControlToolkit.FloatingBehavior, {"handle" : this._dragHandleElement}, null, null, this._foregroundElement); } $addHandler(parent.window, 'resize', this._resizeHandler); // <== This WORKS $addHandler(parent.window, 'scroll', this._scrollHandler); // <== This DOES NOT work this._windowHandlersAttached = true; } Can anybody explain to me why the resize event works while the scroll event doesn't? Any suggestions or alternatives out there to help me out? I am working with jQuery, so if I can use something besides the $addHandler method from MS that'd be fine. Be aware that I also have to override the _detachPopup function to remove the handler, so I need to take that into account. Thanks!

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  • Asp.net grid view

    - by Manoj
    Hello @, I am nt able to edit the details in gridview. When i click on Edit link(Command Field), row editing event is fired but when i click on update link , row editing event is fired again and update event is not getting fired at all. Any suggestions ??

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  • Is this correct for disposing an object using IDisposable

    - by robUK
    I have a class that implements the IDisposable interface. I am using a webclient to download some data using the AsyncDownloadString. I am wondering have I correctly declared my event handlers in the constructor and within the using statement of the web client? And is this correct way to remove the event handlers in the Dispose method? Overrule is this the correct way to use the IDisposable interface? public class Balance : IDisposable { //Constructor WebClient wc; public Balance() { using (wc = new WebClient()) { //Create event handler for the progress changed and download completed events wc.DownloadProgressChanged += new DownloadProgressChangedEventHandler(wc_DownloadProgressChanged); wc.DownloadStringCompleted += new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted); } } ~Balance() { this.Dispose(false); } //Get the current balance for the user that is logged in. //If the balance returned from the server is NULL display error to the user. //Null could occur if the DB has been stopped or the server is down. public void GetBalance(string sipUsername) { //Remove the underscore ( _ ) from the username, as this is not needed to get the balance. sipUsername = sipUsername.Remove(0, 1); string strURL = string.Format("https://www.xxxxxxx.com", sipUsername); //Download only when the webclient is not busy. if (!wc.IsBusy) { // Download the current balance. wc.DownloadStringAsync(new Uri(strURL)); } else { Console.Write("Busy please try again"); } } //return and display the balance after the download has fully completed void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e) { //Pass the result to the event handler } //Dispose of the balance object public void Dispose() { Dispose(true); GC.SuppressFinalize(this); } //Remove the event handlers private bool isDisposed = false; private void Dispose(bool disposing) { if (!this.isDisposed) { if (disposing) { wc.DownloadProgressChanged -= new DownloadProgressChangedEventHandler(wc_DownloadProgressChanged); wc.DownloadStringCompleted -= new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted); wc.Dispose(); } isDisposed = true; } } }

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  • Networking Guidelines

    - by ACShorten
    One of the things I have noticed in my years in IT is the changes in networking. In the past networking was pretty simple with the host name and name resolution (via DNS) being pretty simple. Some sites still use this simple networking setup. These days, more complex name resolution, proxies, firewalls, demarcation nd virtualization, can make networking more complex. This can cause issues when installing products with in built networking that can frustrate even seasoned veterans. I have put together a few basic guidelines to hopefully help along with product installation and getting a product to operate in a somewhat complex network setup. All the components of the product (including the infrastructure) need to communicate via a network (even it is within a local machine/host). Ensure any host names referred to within configuration files are accessible via your networking setup. This may mean defining the hosts to the machines, to the DNS for name resolution and even your firewall to allow machines to communicate within your network. Make sure the ports used for any of the infrastructure are accessible (even through your firewall) and are unique within the host. Host duplication can cause the product to fail on startup as the port is already in use. If there are still issues, consider using localhost as your host name. I have used this in so many situations that I tend to use it now as a default anytime I install anything myself. Most Oracle products suggest to use localhost when using dynamic host or dynamic IP addresses and this is no different for the Oracle Utilities Application Framework. If you do use localhost then installing a Loopback Adapter for the operating system is recommended to force networking to a minimum. Usually localhost resolves to 127.0.0.1. When using multiple network connections, especially in a virtualized environment, ensure the host and ports used are relevent for the network cards you have setup. One of the common issues is finding the product is using a vierualized network card only to find that it is not setup for correct networking. If you are using the batch component, do not forget to ensure that the multicast protocol is enabled on your host and that the multicast address and port number specified are valid and accessible from all machines in the batch cluster (if clustering used). The same advice applies if you are using unicast where each host/port combination should be accessible. Hopefully these basic networking recommendations will help minimize any networking issues you might encounter.

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  • error with slap.d while installing any new software

    - by ali haider
    I am trying to install wireshark (this issue is not specific to wireshark) on my ubuntu box and I keep getting the following error for slap.d: Setting up slapd (2.4.23-6ubuntu6.1) ... Creating initial configuration... mkdir: cannot create directory `/etc/ldap/slapd.d': File exists dpkg: error processing slapd (--configure): subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing: slapd Besides uninstalling or trying to update open LDAP or slap.d, is there any other action that can be taken to resolve this issue? I am trying the install as root user & I have tried moving the slap.d conf file so far but without any luck. Any thoughts on troubleshooting/resolving this issue will be quite welcome. thank in advance

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  • Rendering javascript at the server side level. A good or bad idea?

    - by davidhong
    I want to make it clear first: This isn't a question in relation to server-side Javascript or running Javascript server side. This is a question regarding rendering of Javascript code (which will be executed on the client-side) from server-side code. Having said that, take a look at below ASP.net code for example: hlRemoveCategory.Attributes.Add("onclick", "return confirm('Are you sure you want to delete this?');") This is prescribing the client-side onclick event on the server-side. As oppose to: $('a[rel=remove]').bind('click', function(event) { return confirm('Are you sure you want to delete this?'); } Now the question I want to ask is: What is the benefit of rendering javascript from the server-side code? Or the vice-versa? I personally prefer the second way of hooking up client-side UI/behaviour to HTML elements for the following reasons: Server-side does what ever it needs to already, including data-validation, event delegation and etc; and What server-side sees as an event is not necessarily the same process on the client-side. i.e., there are plenty more events on client-side (just look at custom events); and What happens on client-side and on server-side, during an event, could be completely irrelevant and decoupled; and What ever happens on client-side happens on client-side, there is no need for the server to know. Server should process and run what is given to them, how the process comes to life is not really up to them to decide in the event of the client-side events; and so and so forth. These are my thoughts obviously. I want to know what others think and if there has been any discussions on this topic. Topics branching from this argument can reach: Code management: is it easier to render everything from server-side? Separation of concern: is it easier if client-side logic is separated to server-side logic? Efficiency: which is more efficient both in terms of coding and running? At the end of the day, I am trying to move my team to go towards the second approach. There are lot of old guys in this team who are afraid of this change. I just wish to convince them with the right facts and stats. Let me know your thoughts.

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  • How can Swing dialogs even work?

    - by Bart van Heukelom
    If you open a dialog in Swing, for example a JFileChooser, it goes somewhat like this pseudocode: swing event thread { create dialog add listener to dialog close event { returnValue = somethingFromDialog } show dialog (wait until it is closed) return returnValue } My question is: how can this possibly work? As you can see the thread waits to return until the dialog is closed. This means the Swing event thread is blocked. Yet, one can interact with the dialog, which AFAIK requires this thread to run. So how does that work?

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  • Rails belongs_to issues

    - by Rahul
    I was trying to follow the answer provided by this post About Event_calendar.Showing only events for current user and not all events present However when I tried to add the belongs_to user in the event model, it gives me the following error. NameError (undefined local variable or method 'user' for #<Class:0x007fff15d1f6c0>): app/models/event.rb:3:in '<class:Event>' app/models/event.rb:1:in '<top (required)>' app/controllers/calendar_controller.rb:9:in 'index' Rendered .../.rvm/gems/ruby-1.9.3-p194/gems/actionpack-3.2.8/lib/action_dispatch/middleware/templates/rescues/_trace.erb (2.8ms) Rendered .../.rvm/gems/ruby-1.9.3-p194/gems/actionpack-3.2.8/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (2.0ms) Rendered .../.rvm/gems/ruby-1.9.3-p194/gems/actionpack-3.2.8/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (23.6ms) in my user.rb model I have included has_many :events Any idea how to fix this?

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  • TranslateTransform for drag and drop in Silverlight

    - by fuzzyman
    We're trying to implement drag and drop in Silverlight (3). We want users to be able to drag elements from a treeview onto another part of a UI. The parent element is a Grid, and we've been trying to use a TranslateTransform along with the MouseLeftButtonDown, MouseMove (etc) events, as recommended by various online examples. For example: http://www.85turns.com/2008/08/13/drag-and-drop-silverlight-example/ We're doing this in IronPython, but that should be more or less irrelevant. The drag start is correctly initiated, but the item we are dragging appears in the 'wrong' location (offset a few hundred pixels to the right and down from the cursor) and I can't for the life of me work out why. Basic xaml: <Grid x:Name="layout_root"> <Grid.RowDefinitions> <RowDefinition/> <RowDefinition Height="120"/> </Grid.RowDefinitions> <Border x:Name="drag" Background="LightGray" Width="40" Height="15" Visibility="Collapsed" Canvas.ZIndex="10"> <Border.RenderTransform> <TranslateTransform x:Name="transform" X="0" Y="0" /> </Border.RenderTransform> <TextBlock x:Name="dragText" TextAlignment="Center" Foreground="Gray" Text="foo" /> </Border> ... </Grid> The startDrag method is triggered by the MouseLeftButtonDown event (on a TextBlock in a TreeViewItem.Header). onDrag is triggered by MouseMove. In the following code self.root is Application.Current.RootVisual (top level UI element from app.xaml): def startDrag(self, sender, event): self.root.drag.Visibility = Visibility.Visible self.root.dragText.Text = sender.Text position = event.GetPosition(self.root.drag.Parent) self.root.drag.transform.X = position.X self.root.drag.transform.Y = position.Y self.root.CaptureMouse() self._captured = True def onDrag(self, sender, event): if self._captured: position = event.GetPosition(self.root.drag.Parent) self.root.drag.transform.X = position.X self.root.drag.transform.Y = position.Y The dragged item follows the mouse move, but is offset considerably. Any idea what I am doing wrong and how to correct it?

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  • receive values with XML, AS3

    - by VideoDnd
    My example imports XML and has an object rotating on stage. The rotating object is called enemy corresponds to ENEMY in the XML. How do I set the rotation variable to receive values from XML? REASON It seems more difficult to set up variables using external data. I want to understand it better. rotation.fla //LOAD XML var myXML:XML; var myLoader:URLLoader = new URLLoader(); myLoader.load(new URLRequest("enemy.xml")); myLoader.addEventListener(Event.COMPLETE, processXML); //PARSE XML function processXML(e:Event):void { myXML = new XML(e.target.data); trace(myXML.ROGUE.*); trace(myXML); //TEXT var text:TextField = new TextField(); text.text = myXML.ENEMY.*; addChild(text); } //ROTATION function enterFrameHandler(event:Event):void { //==>CODE I WANT TO CHANGE<== enemy.rotationY += 10; } addEventListener(Event.ENTER_FRAME, enterFrameHandler); enemy.xml ENEMY is set to -100, use what you like <?xml version="1.0" encoding="utf-8"?> <BADGUYS> <ENEMY TITLE="sticky">-100</ENEMY> <ROGUE TITLE="slimy">-1000</ROGUE> </BADGUYS>

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  • Can't install drivers for Epson wp-4530

    - by Rick
    It looks like it's installing ok then I get an error: (Reading database ... 177199 files and directories currently installed.) Unpacking epson-inkjet-printer-escpr:i386 (from .../epson-inkjet-printer-escpr_1.3.0-1lsb3.2_i386.deb) ... dpkg: dependency problems prevent configuration of epson-inkjet-printer-escpr:i386: epson-inkjet-printer-escpr:i386 depends on lsb (>= 3.2). dpkg: error processing epson-inkjet-printer-escpr:i386 (--install): dependency problems - leaving unconfigured Errors were encountered while processing: epson-inkjet-printer-escpr:i386 Can anyone help me with this? Tried install under linux mint 14 and ubuntu 12.04 same problem. Tried installing using cups and Software center. Driver is from http://download.ebz.epson.net/dsc/search/01/search/?OSC=LX which is only driver site I can find for this printer Please help

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  • iPhone - how to track touches and allow button taps at the same time?

    - by Jonathan Cohen
    I'm wondering how to track touches anywhere on the iPhone screen and still have UIButtons respond to taps. I subclassed a UIView, made it full screen and the highest view in the hierarchy, and overrode its pointInside:withEvent method. If I return YES, I'm able to track touches anywhere on the screen but the buttons don't respond (likely because the view is instructed to handle and terminate the touch). If I return NO, the touch passes through the view and the buttons respond, but I'm not able to track touches. Do I need to subclass UIButton or is this possible through the responder chain? What am I doing wrong? - (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event{ return NO; } //only works if pointInside:withEvent: returns YES. -(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{ NSLog(@"began"); [self.nextResponder touchesBegan:touches withEvent:event]; } //only works if pointInside:withEvent: returns YES. -(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{ NSLog(@"end"); [self.nextResponder touchesEnded:touches withEvent:event]; }

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  • Abstract out repeated code

    - by CookieMonster
    The code in this event is repeated exactly in two other event handlers. How do I put the repeated code into a method and call that method from the event handlers so I only have to maintain it in one place? I'm not sure how to pass the event args to the calling method. protected void gvDocAssoc_RowDataBound(object sender, GridViewRowEventArgs e) { if (e.Row.RowType == DataControlRowType.DataRow) { if ((Convert.ToString(DataBinder.Eval(e.Row.DataItem, "DETAIL_TYPE_DESC")) == "Transcript") && (Convert.ToString(DataBinder.Eval(e.Row.DataItem, "INSTITUTION_CODE")) == "")) { e.Row.BackColor = System.Drawing.Color.Red; } if ((Convert.ToString(DataBinder.Eval(e.Row.DataItem, "DETAIL_TYPE_DESC")) == "Certified Diploma") && (Convert.ToString(DataBinder.Eval(e.Row.DataItem, "INSTITUTION_CODE")) == "")) { e.Row.BackColor = System.Drawing.Color.Red; } if ((Convert.ToString(DataBinder.Eval(e.Row.DataItem, "DOC_TYPE_DESC")) == "Post Graduate conditions") && (Convert.ToString(DataBinder.Eval(e.Row.DataItem, "INSTITUTION_CODE")) == "")) { e.Row.BackColor = System.Drawing.Color.Red; } } }

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  • GWT Custom Events

    - by Ciarán
    Hey I have a problem getting my head around how custom GWT event Handlers work. I have read quite a bit about the topic and it still is some what foggy. I have read threads here on Stackoverflow like this one http://stackoverflow.com/questions/998621/gwt-custom-event-handler.Could someone explain it in an applied mannar such as the following. I have 2 classes a block and a man class. When the man collides with the block the man fires an event ( onCollision() ) and then the block class listens for that event. Thanks

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  • Cool examples of procedural pixel shader effects?

    - by Robert Fraser
    What are some good examples of procedural/screen-space pixel shader effects? No code necessary; just looking for inspiration. In particular, I'm looking for effects that are not dependent on geometry or the rest of the scene (would look okay rendered alone on a quad) and are not image processing (don't require a "base image", though they can incorporate textures). Multi-pass or single-pass is fine. Screenshots or videos would be ideal, but ideas work too. Here are a few examples of what I'm looking for (all from the RenderMonkey samples): PS - I'm aware of this question; I'm not asking for a source of actual shader implementations but instead for some inspirational ideas -- and the ones at the NVIDIA Shader Library mostly require a scene or are image processing effects. EDIT: this is an open-ended question and I wish there was a good way to split the bounty. I'll award the rep to the best answer on the last day.

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  • Alternative of touchesMoved in Unity3D

    - by Arman
    - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [[event allTouches] anyObject]; CGPoint location = [touch locationInView:touch.view]; CGPoint xLocation = CGPointMake(location.x,racquet_yellow.center.y); racquet_yellow.center = xLocation; } The above event move recquet_yellow(UIImageView) with mouse pointer, or when I move thumb on iPhone screen, I have 3D Object in Unity3D how can I move my object like recquet_yellow. Kindly guide me.

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  • keyup bindings not working in Firefox

    - by Jarred
    Hi. You can see my project here - http://www.inluxphoto.com/custom/jsgallery/index.php I am attempting to make the left and right arrow keys move the slideshow. I was able to get it to work in all browsers by following exactly the instructions on the front page of jqueryfordesigners.com (sorry I am only allowed one link). However, it is necessary that the keyup be unbinded until the animation completes, so the user cannot do a quick double tap of the key, which breaks the show. This led me to the following function - function keyCommands() { //Bind Keys according to keyAssignments function keyCommandBind() { $(document.documentElement).bind('keyup', keyAssignments) } //Bind functions to specific keys function keyAssignments() { if (event.keyCode == 37) { leftArrow(); } if (event.keyCode == 39) { rightArrow(); } if (event.keyCode == 32) { spaceBar(); } } function leftArrow() { //unbind, do stuff, rebind } function rightArrow() { //unbind, do stuff, rebind } function spaceBar() { //unbind, do stuff, rebind } keyCommandBind(); } This works in all browsers except Firefox & Camino. Firebug tells me event (ie event.keyCode) is not defined. That's true, it's not defined, and I understand that. However I don't understand why, if it's not defined, does it work in all other browsers. How can I appropriately define this? Or, am I doing it wrong? Any help would be most appreciated, thanks for your time!

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