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• What's so bad about building XML with string concatenation?

  - by wsanville

  In the thread What’s your favorite “programmer ignorance” pet peeve?, the following answer appears, with a large amount of upvotes: Programmers who build XML using string concatenation. My question is, why is building XML via string concatenation (such as a StringBuilder in C#) bad? I've done this several times in the past, as it's sometimes the quickest way for me to get from point A to point B when to comes to the data structures/objects I'm working with. So far, I have come up with a few reasons why this isn't the greatest approach, but is there something I'm overlooking? Why should this be avoided? Probably the biggest reason I can think of is you need to escape your strings manually, and most programmers will forget this. It will work great for them when they test it, but then "randomly" their apps will fail when someone throws an & symbol in their input somewhere. Ok, I'll buy this, but it's really easy to prevent the problem (SecurityElement.Escape to name one). When I do this, I usually omit the XML declaration (i.e. <?xml version="1.0"?>). Is this harmful? Performance penalties? If you stick with proper string concatenation (i.e. StringBuilder), is this anything to be concerned about? Presumably, a class like XmlWriter will also need to do a bit of string manipulation... There are more elegant ways of generating XML, such as using XmlSerializer to automatically serialize/deserialize your classes. Ok sure, I agree. C# has a ton of useful classes for this, but sometimes I don't want to make a class for something really quick, like writing out a log file or something. Is this just me being lazy? If I am doing something "real" this is my preferred approach for dealing w/ XML.

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• How can I programmatically position a view using relative points?

  - by Steve Madsen

  What is the best way to position a view relative to the size of its superview, when the bounds of the superview are not yet known? I am trying to avoid hard-coding coordinates if it is at all possible. Perhaps this is silly, and if so, that's a perfectly acceptable answer. I've run into this many times when working with custom UI. The most recent example is that I'm trying to replace the UINavigationItem plain-text title with a custom view. I want that view to fill the superview, but in addition, I want a UIActivityIndicatorView on the right side, inset about 2 pixels and centered vertically. Here's the code: - (void) viewDidLoad { [super viewDidLoad]; customTitleView = [[UIView alloc] initWithFrame:CGRectZero]; customTitleView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth; titleLabel = [[UILabel alloc] initWithFrame:CGRectZero]; titleLabel.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth; titleLabel.lineBreakMode = UILineBreakModeWordWrap; titleLabel.numberOfLines = 2; titleLabel.minimumFontSize = 11.0; titleLabel.font = [UIFont systemFontOfSize:17.0]; titleLabel.adjustsFontSizeToFitWidth = YES; [customTitleView addSubview:titleLabel]; spinnerView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite]; spinnerView.center = CGPointMake(customTitleView.bounds.size.width - (spinnerView.bounds.size.width / 2) - 2, customTitleView.bounds.size.height / 2); spinnerView.hidesWhenStopped = YES; [customTitleView addSubview:spinnerView]; self.navigationItem.titleView = customTitleView; [customTitleView release]; } Here's my problem: at the time that this code runs, customTitleView.bounds is still zeroes. The auto-resizing mask hasn't had a chance to do its thing yet, but I very much want those values so that I can compute the relative positions of other sub-views (here, the activity indicator). Is this possible without being ugly?

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• Flash AS3: How to Make scroll bar react to dynamic textfield movement?

  - by HeroicNate

  I've been looking for a tutorial and answer to this for a while but can't find what I'm looking for. I am loading html text into a dynamic textfield, and I have a scrollbar controlling the scroll using the code below. What I want to do is also add scroll up/down buttons and have the scroll bar move in relation to the text scroll. I was just going to use "tracklistingtext.scrollV -- " for the scroll buttons, but right now the scroll bar doesn't recognize the text movement. What do I need to do to get the scroll bar to listen to the text scroll position? var listTextreq:URLRequest=new URLRequest("tracklist.txt"); var listTextLoader:URLLoader = new URLLoader(); var bounds:Rectangle=new Rectangle(scrollMC.x,scrollMC.y,0,300); var scrolling:Boolean=false; function fileLoaded(event:Event):void { tracklistingtext.htmlText=listTextLoader.data; tracklistingtext.multiline=true; tracklistingtext.wordWrap=true; scrollMC.addEventListener(MouseEvent.MOUSE_DOWN, startScroll); stage.addEventListener(MouseEvent.MOUSE_UP, stopScroll); addEventListener (Event.ENTER_FRAME, enterHandler); } listTextLoader.addEventListener(Event.COMPLETE, fileLoaded); listTextLoader.load(listTextreq); function startScroll(e:Event):void { scrolling=true; scrollMC.startDrag(false,bounds); } function stopScroll(e:Event):void { scrolling=false; scrollMC.stopDrag(); } function enterHandler (e:Event):void { if (scrolling == true) { tracklistingtext.scrollV = Math.round(((scrollMC.y - bounds.y)/300)*tracklistingtext.maxScrollV); } } Any help is greatly appreciated.

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• Objective-C Definedness

  - by Dan Ray

  This is an agonizingly rookie question, but here I am learning a new language and framework, and I'm trying to answer the question "What is Truth?" as pertains to Obj-C. I'm trying to lazy-load images across the network. I have a data class called Event that has properties including: @property (nonatomic, retain) UIImage image; @property (nonatomic, retain) UIImage thumbnail; in my AppDelegate, I fetch up a bunch of data about my events (this is an app that shows local arts event listings), and pre-sets each event.image to my default "no-image.png". Then in the UITableViewController where I view these things, I do: if (thisEvent.image == NULL) { NSLog(@"Going for this item's image"); UIImage *tempImage = [UIImage imageWithData:[NSData dataWithContentsOfURL: [NSURL URLWithString: [NSString stringWithFormat: @"http://www.mysite.com/content_elements/%@_image_1.jpg", thisEvent.guid]]]]; thisEvent.image = tempImage; } We never get that NSLog call. Testing thisEvent.image for NULLness isn't the thing. I've tried == nil as well, but that also doesn't work.

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• Forwarding HTTP Request with Direct Server Return

  - by Daniel Crabtree

  I have servers spread across several data centers, each storing different files. I want users to be able to access the files on all servers through a single domain and have the individual servers return the files directly to the users. The following shows a simple example: 1) The user's browser requests http://www.example.com/files/file1.zip 2) Request goes to server A, based on the DNS A record for example.com. 3) Server A analyzes the request and works out that /files/file1.zip is stored on server B. 4) Server A forwards the request to server B. 5) Server B returns file1.zip directly to the user without going through server A. Note: steps 4 and 5 must be transparent to the user and cannot involve sending a redirect to the user as that would violate the requirement of a single domain. From my research, what I want to achieve is called "Direct Server Return" and it is a common setup for load balancing. It is also sometimes called a half reverse proxy. For step 4, it sounds like I need to do MAC Address Translation and then pass the request back onto the network and for servers outside the network of server A tunneling will be required. For step 5, I simply need to configure server B, as per the real servers in a load balancing setup. Namely, server B should have server A's IP address on the loopback interface and it should not answer any ARP requests for that IP address. My problem is how to actually achieve step 4? I have found plenty of hardware and software that can do this for simple load balancing at layer 4, but these solutions fall short and cannot handle the kind of custom routing I require. It seems like I will need to roll my own solution. Ideally, I would like to do the routing / forwarding at the web server level, i.e. in PHP or C# / ASP.net. However, I am open to doing it at a lower level such as Apache or IIS, or at an even lower level, i.e. a custom proxy service in front of everything.

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• Qt display image in a new window

  - by user312543

  Hi, I am naive to Qt and GUI programming. http://stackoverflow.com/questions/1357960/qt-jpg-image-display/2605463#2605463 The procedure given for displaying an image is working fine and thank you for providing that. But I want to display an image when I click on radiobutton. I created a slot, and I connected the button click event to the slot (dispImage is my slot). My slot consists only the code which is working to display an image (First answer in this link). I am able to compile it and run it. But the o/p is not as we desire. On button click, image windoe flashes for a sec and disappears. One more point to share is, I tried the same with windowsflags example present in qt examples. In this example I want to display the image on the preview window created by us. Even this is also not worked for me. Please provide me the solution. Thanks in advance.

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• My app crash with MFMailComposeViewController and MFMessageComposeViewController when I re-launch it.

  - by Dolwen

  Hello all, I encounter a crash with MFMailComposeViewController, MFMessageComposeViewController and multitasking on IOS 4.2 (both simulator and IPHone 4). Code i use : Class emailClass = (NSClassFromString(@"MFMailComposeViewController")); if( emailClass != nil ) { MFMailComposeViewController * controller = [[emailClass alloc] init]; if([emailClass canSendMail]) { // delegate controller.mailComposeDelegate = self; // subject [controller setSubject:@"Hello All."]; // main message [controller setMessageBody:@"I love Stackoverflow.com !" isHTML:NO]; // adding image attachment // getting path for the image we have in the tutorial project NSString *path = [[NSBundle mainBundle] pathForResource:@"image" ofType:@"png"]; // loading content of the image into NSData NSData *imageData = [NSData dataWithContentsOfFile:path]; // adding the attachment to he message [controller addAttachmentData:imageData mimeType:@"image/png" fileName:@"My Byook image"]; // setting different than the default transition for the modal view controller [controller setModalTransitionStyle:UIModalTransitionStyleCoverVertical]; // show [[CGameStateManager getCurrentGameState] presentModalViewController:controller animated:YES]; } [controller release]; } To close MFMailComposeViewController i use : [[CGameStateManager getCurrentGameState] dismissModalViewControllerAnimated:NO]; Then the app crash on the "dismissModalViewControllerAnimated:" and we can read in the debugger with NSZombieEnabled : * -[UIImage isKindOfClass:]: message sent to deallocated instance 0xb0b9f80 Anyone have an answer to solve my problem ? :) Thx

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• Disabling browser print options (headers, footers, margins) from page?

  - by Anthony

  I have seen this question asked in a couple of different ways on SO and several other websites, but most of them are either too specific or out-of-date. I'm hoping someone can provide a definitive answer here without pandering to speculation. Is there a way, either with CSS or javascript, to change the default printer settings when someone prints within their browser? And of course by "prints from their browser" I mean some form of HTML, not PDF or some other plug-in reliant mime-type. Please note: If some browsers offer this and others don't (or if you only know how to do it for some browsers) I welcome browser-specific solutions. Similarly, if you know of a mainstream browser that has specific restrictions against EVER doing this, that is also helpful, but some fairly up-to-date documentation would be appreciated. (simply saying "that goes against XYZ's security policy" isn't very convincing when XYZ has made significant changes in said policy in the last three years). Finally, when I say "change default print settings" I don't mean forever, just for my page, and I am referring specifically to print margins, headers, and footers. I am very aware that CSS offers the option of changing the page orientation as well as the page margins. One of the many struggles is with Firefox. If I set the page margins to 1 inch, it ADDS this to the half inch it already puts into place. I very much want to reduce the usage of PDFs on my client's site, but the infringement on presentation (as well as the lack of reliability) are their main concern.

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• Thread mutex behaviour

  - by Alberteddu

  Hi there, I'm learning C. I'm writing an application with multiple threads; I know that when a variable is shared between two or more threads, it is better to lock/unlock using a mutex to avoid deadlock and inconsistency of variables. This is very clear when I want to change or view one variable. int i = 0; /** Global */ static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /** Thread 1. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); /** Thread 2. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); This is correct, I think. The variable i, at the end of the executions, contains the integer 2. Anyway, there are some situations in which I don't know exactly where to put the two function calls. For example, suppose you have a function obtain(), which returns a global variable. I need to call that function from within the two threads. I have also two other threads that call the function set(), defined with a few arguments; this function will set the same global variable. The two functions are necessary when you need to do something before getting/setting the var. /** (0) */ /** Thread 1, or 2, or 3... */ if(obtain() == something) { if(obtain() == somethingElse) { // Do this, sometimes obtain() and sometimes set(random number) (1) } else { // Do that, just obtain(). (2) } } else { // Do this and do that (3) // If # of thread * 3 > 10, then set(3*10) For example. (4) } /** (5) */ Where I have to lock, and where I have to unlock? The situation can be, I think, even more complex. I will appreciate an exhaustive answer. Thank you in advance. —Alberto

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• How to catch unintentional function interpositioning?

  - by SiegeX

  Reading through my book Expert C Programming, I came across the chapter on function interpositioning and how it can lead to some serious hard to find bugs if done unintentionally. The example given in the book is the following: my_source.c mktemp() { ... } main() { mktemp(); getwd(); } libc mktemp(){ ... } getwd(){ ...; mktemp(); ... } According to the book, what happens in main() is that mktemp() (a standard C library function) is interposed by the implementation in my_source.c. Although having main() call my implementation of mktemp() is intended behavior, having getwd() (another C library function) also call my implementation of mktemp() is not. Apparently, this example was a real life bug that existed in SunOS 4.0.3's version of lpr. The book goes on to explain the fix was to add the keyword static to the definition of mktemp() in my_source.c; although changing the name altogether should have fixed this problem as well. This chapter leaves me with some unresolved questions that I hope you guys could answer: Does GCC have a way to warn about function interposition? We certainly don't ever intend on this happening and I'd like to know about it if it does. Should our software group adopt the practice of putting the keyword static in front of all functions that we don't want to be exposed? Can interposition happen with functions introduced by static libraries? Thanks for the help. EDIT I should note that my question is not just aimed at interposing over standard C library functions, but also functions contained in other libraries, perhaps 3rd party, perhaps ones created in-house. Essentially, I want to catch any instance of interpositioning regardless of where the interposed function resides.

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• Help! I'm a Haskell Newbie

  - by Darknight

  I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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• Can we solve the table row background image problem, in chrome, in multi celled tables??

  - by Ya'el

  It is frequently asked – but I haven’t seen a good answer yet (and I looked). If you set a background image in CSS to a table row- the image will repeat itself in every cell. If you set the position: relative (for the row) and set the background-image: none (for the cells) it solves the problem on IE but not on chrome! I can't use background positioning since there are many calls and their size varies. (And the picture is not symmetrical- It's a fade out from one side. Anybody?? Example for the css code : tr { height: 30px; position:relative;} tr.green {background: url('green_30.png') no-repeat left top;} tr.orange {background: url('oranger_30.png') no-repeat left top;} tr.red {background: url('red_30.png') no-repeat left top;} td {background-image:none;} The HTML is basic - A multi cell table. The goal is to have different colors fade into every row, but it could be any non-pattern image.

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• Is there a way to specify a per-host deploy_to path with Capistrano?

  - by Chad Johnson

  I have searched and searched and asked a question already and have not received a clear answer. I have the following deploy script (snippet): set :application, "testapplication" set :repository, "ssh://domain.com//srv/hg/#{application}" set :scm, :mercurial set :deploy_to, "/srv/www/#{application}" role :web, "domain1.com", "domain2.com" role :app, "domain1.com", "domain2.com" role :db, "domain1.com", :primary => true, :norelease => true role :db, "domain2.com", :norelease => true As you see, I have set deploy_to to a specific path. And, I also have specified multiple web servers. However, each web server should have a different deployment path. I want to be able to run "cap deploy" and deploy to all hosts in one shot. I am NOT trying to deploy to staging and then to production. This is all production. My question is: how exactly do I specify a path per server? I have read the "Roles" documentation for Capistrano, and this is unclear. Can someone please post a deploy file example? I have read the documentation, and it is unclear how to do this. Does anyone know? Am I crazy? Am I thinking of this wrong or something? No answers anywhere online. Nowhere. Nothing. Please, someone help.

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• Inline function v. Macro in C -- What's the Overhead (Memory/Speed)?

  - by Jason R. Mick

  I searched Stack Overflow for the pros/cons of function-like macros v. inline functions. I found the following discussion: Pros and Cons of Different macro function / inline methods in C ...but it didn't answer my primary burning question. Namely, what is the overhead in c of using a macro function (with variables, possibly other function calls) v. an inline function, in terms of memory usage and execution speed? Are there any compiler-dependent differences in overhead? I have both icc and gcc at my disposal. My code snippet I'm modularizing is: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = AttractiveTerm * AttractiveTerm; EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); My reason for turning it into an inline function/macro is so I can drop it into a c file and then conditionally compile other similar, but slightly different functions/macros. e.g.: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = pow(SigmaSquared/RadialDistanceSquared,9); EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); (note the difference in the second line...) This function is a central one to my code and gets called thousands of times per step in my program and my program performs millions of steps. Thus I want to have the LEAST overhead possible, hence why I'm wasting time worrying about the overhead of inlining v. transforming the code into a macro. Based on the prior discussion I already realize other pros/cons (type independence and resulting errors from that) of macros... but what I want to know most, and don't currently know is the PERFORMANCE. I know some of you C veterans will have some great insight for me!!

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• Change HTML image into a Button for partial refresh of page

  - by user990951

  I am new to webpage design and MVC. I have a aspx page and I have a html image. I want to change this image and make it clickable so that it will refresh only the bottom half of the page when clicked. I setup my image so that the source of the image is updated by the controller. By using the following src="<%=ViewData["BookImg"] %>" So that the whole story is clear. When a person clicks on the image of the book, it displays on the bottom half of the page information about that book pulled from a sql database. I am thinking that I would need to look into getting ajax implemented so that I can do partial page update. But the question is how do I change that HTML image into a button. Thanks in advance. ---updating per the answer chosen but still having problems--- home.aspx <% Html.RenderPartial("HomePartialView"); %> <img id = "Book_Img" src="<%=ViewData["BookImg"] %>" alt = "click Me" class="imgClick"/> <script src="../../Scripts/jquery-1.5.1.js" type="text/javascript"> $(document).ready(function(){ $(".imgClick").click(function () { $("HomePartialView").load("../../Controllers/HomeController/PartialViewBook"); }); }); </script> ---Controller public ActionResult PartialViewBook() { ViewData[imageBookPressd] = "hello world"; return View("HomePartialView"); }

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• Serialization of Queue type not working

  - by Soham

  Consider this piece of code: private Queue Date=new Queue(); //other declarations public DateTime _Date { get { return (DateTime)Date.Peek();} set { Date.Enqueue(value); } } //other properties and stuff.... public void UpdatePosition(...) { //other code IFormatter formatter = new BinaryFormatter(); Stream Datestream = new MemoryStream(); formatter.Serialize(Datestream, Date); byte[] Datebin = new byte[2048]; Datestream.Read(Datebin,0,2048); //Debug-Bug Console.WriteLine(Convert.ToString(this._Date)); Console.WriteLine(BitConverter.ToString(Datebin, 0, 3)); //other code } The output of the first WriteLine is perfect. I.e to check if really the Queue is initialised or not. It is. The right variables are stored etc. (I inserted a value in that Queue, that part of the code is not shown.) But the second WriteLine is not giving the right expected answer: It serializes the entire Queue to 00-00-00.

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• The most expressive web app programming language/framework combination?

  - by Thor

  When concerned about creating web applications, I often ask myself how I can make the code easy to read and above all; how to make it easy to maintain. There has been alot of inventions in the last couple of years with probably millions of programmers sharing these thoughts. So, lets test if we can squeeze the distilled knowledge of millions of StackOverflow users for this ultimate answer: Which language/framework combination in the world right now is the most expressive to do common tasks? Please provide a simple example of simplicity, add a link to more information about the language, and no more than one entry per language/framework combination. Specifications: "Web application" in this context refers to applications that runs on a server and outputs HTML/Javascript/CSS for rendering on a client browser. Any server operating system is ok. "Language/Framework combination" can for example be like Java+Struts or Java+SpringWeb or Perl+CGI or Java+ZK "Most expressive" in this context is meant to be minimal code to do common tasks. "Common tasks" include simple output/input, i.e. form specifying, displaying and processing, as well as simply styling of output. I am more concerned about minimality than about complete functionality. A decent language design can have great potential even though it is not complete.

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• How to convert "0" and "1" to false and true

  - by Chris

  I have a method which is connecting to a database via Odbc. The stored procedure which I'm calling has a return value which from the database side is a 'Char'. Right now I'm grabbing that return value as a string and using it in a simple if statement. I really don't like the idea of comparing a string like this when only two values can come back from the database, 0 and 1. OdbcCommand fetchCommand = new OdbcCommand(storedProc, conn); fetchCommand.CommandType = CommandType.StoredProcedure; fetchCommand.Parameters.AddWithValue("@column ", myCustomParameter); fetchCommand.Parameters.Add("@myReturnValue", OdbcType.Char, 1). Direction = ParameterDirection.Output; fetchCommand.ExecuteNonQuery(); string returnValue = fetchCommand.Parameters["@myReturnValue"].Value.ToString(); if (returnValue == "1") { return true; } What would be the proper way to handle this situation. I've tried 'Convert.ToBoolean()' which seemed like the obvious answer but I ran into the 'String was not recognized as a valid Boolean. ' exception being thrown. Am I missing something here, or is there another way to make '1' and '0' act like true and false? Thanks!

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• Set DetailsView as selected row of GridView

  - by Nix

  I am afraid this is a brain fart question. But I have searched around and have not been able to find the answer. I am creating a GridView/DetailsView page. I have a grid that displays a bunch of rows, when a row is selected it uses a DetailsView to allow for Insert/Update. My question is what is the best way to link these? I do not want to reach out to the web service again, all the data i need is in the selected grid view row. I basically have 2 separate data sources that share the same "DataObjectTypeName", the first data source retrieves the data, and the other to do the CRUD. What is the best way to transfer the Selected Grid View row to the Details View? Am I going to have to manualy handle the Insert/Update events and call the data source myself? <asp:GridView ID="gvDetails" runat="server" DataKeyNames="ID, Code" DataSourceID="odsSearchData" > <Columns> <asp:BoundField DataField="RowA" HeaderText="A" SortExpression="RowA" /> <asp:BoundField DataField="RowB" HeaderText="B" SortExpression="RowB" /> <asp:BoundField DataField="RowC" HeaderText="C" SortExpression="RowC" /> ....Code... <asp:DetailsView ID="dvDetails" runat="server" DataKeyNames="ID, Code" DataSourceID="odsCRUD" GridLines="None" DefaultMode="Edit" AutoGenerateRows="false" Visible="false" Width="100%"> <Fields> <asp:BoundField DataField="RowA" HeaderText="A" SortExpression="RowA" /> <asp:BoundField DataField="RowB" HeaderText="B" SortExpression="RowB" /> <asp:BoundField DataField="RowC" HeaderText="C" SortExpression="RowC" /> ...

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• Which OpenGL functions are not GPU-accelerated?

  - by Xavier Ho

  I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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• Passing Extras and screen rotation

  - by Luis A. Florit

  This kind of questions appear periodically. Sorry if this has been covered before, but I'm a newbie and couldn't find the appropriate answer. It deals with the correct implementation of communication between classes and activities. I made a gallery app. It has 3 main activities: the Main one, to search for filenames using a pattern; a Thumb one, that shows all the images that matched the pattern as thumbnails in a gridview, and a Photo activity, that opens a full sized image when you click a thumb in Thumbs. I pass to the Photo activity via an Intent the filenames (an array), and the position (an int) of the clicked thumb in the gridview. This third Photo activity has only one view on it: a TouchImageView, that I adapted for previous/next switching and zooming according to where you shortclick on the image (left, right or middle). Moreover, I added a longclick listener to Photo to show EXIF info. The thing is working, but I am not happy with the implementation... Some things are not right. One of the problems I am experiencing is that, if I click on the right of the image to see the next in the Photo activity, it switches fine (position++), but when rotating the device the original one at position appears. What is happening is that Photo is destroyed when rotating the image, and for some reason it restarts again, without obeying super.onCreate(savedInstanceState), loading again the Extras (the position only changed in Photo, not on the parent activities). I tried with startActivityForResult instead of startActivity, but failed... Of course I can do something contrived to save the position data, but there should be something "conceptual" that I am not understanding about how activities work, and I want to do this right. Can someone please explain me what I am doing wrong, which is the best method to implement what I want, and why? Thanks a lot!!!

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• Why doesn't this CompiledQuery give a performance improvement?

  - by Grammarian

  I am trying to speed up an often used query. Using a CompiledQuery seemed to be the answer. But when I tried the compiled version, there was no difference in performance between the compiled and non-compiled versions. Can someone please tell me why using Queries.FindTradeByTradeTagCompiled is not faster than using Queries.FindTradeByTradeTag? static class Queries { // Pre-compiled query, as per http://msdn.microsoft.com/en-us/library/bb896297 private static readonly Func<MyEntities, int, IQueryable<Trade>> mCompiledFindTradeQuery = CompiledQuery.Compile<MyEntities, int, IQueryable<Trade>>( (entities, tag) => from trade in entities.TradeSet where trade.trade_tag == tag select trade); public static Trade FindTradeByTradeTagCompiled(MyEntities entities, int tag) { IQueryable<Trade> tradeQuery = mCompiledFindTradeQuery(entities, tag); return tradeQuery.FirstOrDefault(); } public static Trade FindTradeByTradeTag(MyEntities entities, int tag) { IQueryable<Trade> tradeQuery = from trade in entities.TradeSet where trade.trade_tag == tag select trade; return tradeQuery.FirstOrDefault(); } }

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• Android newbie installing Eclipse, having issues....

  - by Jeff

  I am a web developer, new to app development and Java/Android. I am about to follow some tutorials to get started learning but I'm running into a wall. The Android dev site says the recommended way to build Android apps is in Java using the Eclipse plug in. So I downloaded Eclipse Classic and unzipped it on to get this error: "A Java Runtime Environment (JRE) or Java Development Kit (JDK) must be available in order to run Eclipse. No Java virtual machine was found after searching the following locations: /Users//Desktop/eclipse/Eclipse.app/Contents/MacOS/jre/bin/java java in your current PATH" Any idea what the issue is and how I can fix it? Again, newbie to java, jre, android, so I apologize if this question has already been asked. In my research I've discovered that most of the posts or solutions I've found are tough for me to follow. There's always a few unclear items that are probably prohibiting me from getting the answer I need. So I'm hoping someone can walk me through installing or configuring whatever I need to regarding Java so I can continue installing Eclipse and begin learning. I should probably note that I'm on Mac OSX 10.6.6 Snow Leopard. Please let me know if you need any other info. Thanks so much in advance for any and all help!!!

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• Where are possible locations of queueing/buffering delays in Linux multicast?

  - by Matt

  We make heavy use of multicasting messaging across many Linux servers on a LAN. We are seeing a lot of delays. We basically send an enormous number of small packages. We are more concerned with latency than throughput. The machines are all modern, multi-core (at least four, generally eight, 16 if you count hyperthreading) machines, always with a load of 2.0 or less, usually with a load less than 1.0. The networking hardware is also under 50% capacity. The delays we see look like queueing delays: the packets will quickly start increasing in latency, until it looks like they jam up, then return back to normal. The messaging structure is basically this: in the "sending thread", pull messages from a queue, add a timestamp (using gettimeofday()), then call send(). The receiving program receives the message, timestamps the receive time, and pushes it in a queue. In a separate thread, the queue is processed, analyzing the difference between sending and receiving timestamps. (Note that our internal queues are not part of the problem, since the timestamps are added outside of our internal queuing.) We don't really know where to start looking for an answer to this problem. We're not familiar with Linux internals. Our suspicion is that the kernel is queuing or buffering the packets, either on the send side or the receive side (or both). But we don't know how to track this down and trace it. For what it's worth, we're using CentOS 4.x (RHEL kernel 2.6.9).

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• How do I format a Uri when binding an Image in Silverlight?

  - by Scott

  I haven't been able to find an answer to this. I have a database that has image paths in it ("images/myimage.jpg"). These images exist on my asp.net site which is also where I host the SL. I want to bind these images to my ListBox control so that the image displays. I have read that since I have a string value, "images/myimage.jpg", that I need to convert it to a BitMap image. I have done this: the xaml: <Image Source="{Binding ImageFile, Converter={StaticResource ImageConverter}}"/> the ImageConverter class: public object Convert(object value, Type targetType, object parameter, CultureInfo culture) { try { Uri source= new Uri(value.ToString()); return new BitmapImage(source); } catch(Exception ex) { return new BitmapImage(); } } I get an error when creating the Uri, "The Format of the URI could not be determined". What am I doing wrong? If I create a Uri that looks like this: http://localhost:49723/images/myimage.jpg, it works just fine. Why doesn't just "images/myimage.jpg" work?

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