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• CDI SessionScoped Bean instance remains unchanged when login with different user

  - by Jason Yang

  I've been looking for the workaround of this problem for rather plenty of time and no result, so I ask question here. Simply speaking, I'm using a CDI SessionScoped Bean User in my project to manage user information and display them on jsf pages. Also container-managed j_security_check is used to resolve authentication issue. Everything is fine if first logout with session.invalidate() and then login in the same browser tab with a different user. But when I tried to directly login (through login.jsf) with a new user without logout beforehand, I found the user information remaining unchanged. I debugged and found the User bean, as well as the HttpSession instance, always remaining the same if login with different users in the same browser, as long as session.invalidate() not invoked. But oddly, the session id did modified, and I've both checked in Java code and Firebug. org.apache.catalina.session.StandardSessionFacade@5d7b4092 StandardSession[c69a71d19f369d08b5dddbea2ef0] attrName = org.jboss.weld.context.conversation.ConversationIdGenerator : attrValue=org.jboss.weld.context.conversation.ConversationIdGenerator@583c9dd8 attrName = org.jboss.weld.context.ConversationContext.conversations : attrValue = {} attrName = org.jboss.weld.context.http.HttpSessionContext#org.jboss.weld.bean-Discipline-ManagedBean-class com.netease.qa.discipline.profile.User : attrValue = Bean: Managed Bean [class com.netease.qa.discipline.profile.User] with qualifiers [@Any @Default @Named]; Instance: com.netease.qa.discipline.profile.User@c497c7c; CreationalContext: org.jboss.weld.context.CreationalContextImpl@739efd29 attrName = javax.faces.request.charset : attrValue = UTF-8 org.apache.catalina.session.StandardSessionFacade@5d7b4092 StandardSession[c6ab4b0c51ee0a649ef696faef75] attrName = org.jboss.weld.context.conversation.ConversationIdGenerator : attrValue = org.jboss.weld.context.conversation.ConversationIdGenerator@583c9dd8 attrName = com.sun.faces.renderkit.ServerSideStateHelper.LogicalViewMap : attrValue = {-4968076393130137442={-7694826198761889564=[Ljava.lang.Object;@43ff5d6c}} attrName = org.jboss.weld.context.ConversationContext.conversations : attrValue = {} attrName = org.jboss.weld.context.http.HttpSessionContext#org.jboss.weld.bean-Discipline-ManagedBean-class com.netease.qa.discipline.profile.User : attrValue = Bean: Managed Bean [class com.netease.qa.discipline.profile.User] with qualifiers [@Any @Default @Named]; Instance: com.netease.qa.discipline.profile.User@c497c7c; CreationalContext: org.jboss.weld.context.CreationalContextImpl@739efd29 attrName = javax.faces.request.charset : attrValue = UTF-8 Above block contains two successive logins and their Session info. We can see that the instance(1st row) the same while session id(2nd row) different. Seems that session object is reused to contain different session id and CDI framework manages session bean life cycle in accordance with the session object only(?). I'm wondering whether there could be only one server-side session object within the same browser unless invalidated? Since I'm adopting j_security_check I fancy intercepting it and invalidating old session is not so easy. So is it possible to accomplish the goal without altering the CDI+JSF+j_security_check design that one can relogin with different account in the same or different tab within the same browser? Really look forward for your response. More info: Glassfish v3.1 is my appserver.

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• Calculations in a table of data

  - by Christian W

  I have a table of data with survey results, and I want to do certain calculations on this data. The datastructure is somewhat like this: ____________________________________________________________________________________ | group |individual | key | key | key | | | |subkey|subkey|subkey|subkey|subkey|subkey|subkey|subkey|subkey| | | |q|q|q |q |q |q|q|q |q|q|q |q |q |q|q|q |q|q|q |q |q |q|q|q | |-------|-----------|-|-|--|--|---|-|-|--|-|-|--|--|---|-|-|--|-|-|--|--|---|-|-|--| | 1 | 0001 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 1 | 0002 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 1 | 0003 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 2 | 0004 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 2 | 0005 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 3 | 0006 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 4 | 0007 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | ------------------------------------------------------------------------------------ Excuse my poor ascii skills... So, every individual belongs to a group, and has answered some questions. These questions are always grouped in keys and subkeys. Is there any simple method to calculate averages, deviations and similar based on the groupings. Something like public float getAverage(int key, int individual); float avg = getAverage(5,7); I think what I'm asking is what would be the best way to structure the data in C# to make it as easy as possible to work with? I have started making classes for every entity, but I got confused somewhere and something stopped working. So before I continue along this path, I was wondering if there are any other, better, ways of doing this? (Every individual can also have describing variables, like agegroup and such, but that's not important for the base functionality.) Our current solution does all calculations inline in the queries when requesting the data from the database. This works, but it's slow and the number of queries equals questions * individuals + keys * individuals, which could be alot if individual queries. Any suggestions?

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• Asynchronous vs Synchronous vs Threading in an iPhone App

  - by Coocoo4Cocoa

  I'm in the design stage for an app which will utilize a REST web service and sort of have a dilemma in as far as using asynchronous vs synchronous vs threading. Here's the scenario. Say you have three options to drill down into, each one having its own REST-based resource. I can either lazily load each one with a synchronous request, but that'll block the UI and prevent the user from hitting a back navigation button while data is retrieved. This case applies almost anywhere except for when your application requires a login screen. I can't see any reason to use synchronous HTTP requests vs asynchronous because of that reason alone. The only time it makes sense is to have a worker thread make your synchronous request, and notify the main thread when the request is done. This will prevent the block. The question then is bench marking your code and seeing which has more overhead, a threaded synchronous request or an asynchronous request. The problem with asynchronous requests is you need to either setup a smart notification or delegate system as you can have multiple requests for multiple resources happening at any given time. The other problem with them is if I have a class, say a singleton which is handling all of my data, I can't use asynchronous requests in a getter method. Meaning the following won't go: - (NSArray *)users { if(users == nil) users = do_async_request // NO GOOD return users; } whereas the following: - (NSArray *)users { if(users == nil) users == do_sync_request // OK. return users; } You also might have priority. What I mean by priority is if you look at Apple's Mail application on the iPhone, you'll notice they first suck down your entire POP/IMAP tree before making a second request to retrieve the first 2 lines (the default) of your message. I suppose my question to you experts is this. When are you using asynchronous, synchronous, threads -- and when are you using either async/sync in a thread? What kind of delegation system do you have setup to know what to do when a async request completes? Are you prioritizing your async requests? There's a gamut of solutions to this all too common problem. It's simple to hack something out. The problem is, I don't want to hack and I want to have something that's simple and easy to maintain.

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• fill gridview cell-by-cell

  - by raging_boner

  I want to populate GridView below with images: <asp:GridView ID="GrdDynamic" runat="server" AutoGenerateColumns="False"> <Columns> </Columns> </asp:GridView> The code below iterates through directory, then I collect image titles and want them to be populated in gridview. code in bold is not working well, gridview is only filled with the last image in list. List<string> imagelist = new List<string>(); protected void Page_Load(object sender, EventArgs e) { foreach (String image in Directory.GetFiles(Server.MapPath("example/"))) { imagelist.Add("~/example/" + Path.GetFileName(image)); } loadDynamicGrid(imagelist); } private void loadDynamicGrid(List<string> list) { DataTable dt = new DataTable(); DataColumn dcol = new DataColumn(NAME, typeof(System.String)); dt.Columns.Add(dcol); dcol = new DataColumn("NAME1", typeof(System.String)); dt.Columns.Add(dcol); dcol = new DataColumn("NAME2", typeof(System.String)); dt.Columns.Add(dcol); dcol = new DataColumn("NAME3", typeof(System.String)); dt.Columns.Add(dcol); DataRow drow = dt.NewRow(); dt.Rows.Add(); dt.Rows.Add(); **for (int i = 0; i < dt.Rows.Count; i++) { for (int j = 0; j < dt.Columns.Count; j++) { foreach (string value in list) { dt.Rows[i][j] = value; } } }** foreach (DataColumn col in dt.Columns) { ImageField bfield = new ImageField(); bfield.DataImageUrlField = NAME; bfield.HeaderText = col.ColumnName; GrdDynamic.Columns.Add(bfield); } GrdDynamic.DataSource = dt; GrdDynamic.DataBind(); } how to fill gridview cell-by-cell only with available amount of images? i know it is easy, i tried various methods like: dt.Rows.Add(list); and some other attempts, but they didn't work. i'm very stupid. i'd be glad for any help.

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• Can I access Spring session-scoped beans from application-scoped beans? How?

  - by Corvus

  I'm trying to make this 2-player web game application using Spring MVC. I have session-scoped beans Player and application-scoped bean GameList, which creates and stores Game instances and passes them to Players. On player creates a game and gets its ID from GameList and other player sends ID to GameList and gets Game instance. The Game instance has its players as attributes. Problem is that each player sees only himself instead of the other one. Example of what each player sees: First player (Alice) creates a game: Creator: Alice, Joiner: Empty Second player (Bob) joins the game: Creator: Bob, Joiner: Bob First player refreshes her browser Creator: Alice, Joiner: Alice What I want them to see is Creator: Alice, Joiner: Bob. Easy way to achieve this is saving information about players instead of references to players, but the game object needs to call methods on its player objects, so this is not a solution. I think it's because of aop:scoped-proxy of session-scoped Player bean. If I understand this, the Game object has reference to proxy, which refers to Player object of current session. Can Game instance save/access the other Player objects somehow? beans in dispatcher-servlet.xml: <bean id="userDao" class="authorization.UserDaoFakeImpl" /> <bean id="gameList" class="model.GameList" /> <bean name="/init/*" class="controller.InitController" > <property name="gameList" ref="gameList" /> <property name="game" ref="game" /> <property name="player" ref="player" /> </bean> <bean id="game" class="model.GameContainer" scope="session"> <aop:scoped-proxy/> </bean> <bean id="player" class="beans.Player" scope="session"> <aop:scoped-proxy/> </bean> methods in controller.InitController private GameList gameList; private GameContainer game; private Player player; public ModelAndView create(HttpServletRequest request, HttpServletResponse response) throws Exception { game.setGame(gameList.create(player)); return new ModelAndView("redirect:game"); } public ModelAndView join(HttpServletRequest request, HttpServletResponse response, GameId gameId) throws Exception { game.setGame(gameList.join(player, gameId.getId())); return new ModelAndView("redirect:game"); } called methods in model.gameList public Game create(Player creator) { Integer code = generateCode(); Game game = new Game(creator, code); games.put(code, game); return game; } public Game join(Player joiner, Integer code) { Game game = games.get(code); if (game!=null) { game.setJoiner(joiner); } return game; }

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• What to do when you need more verbs in REST

  - by Richard Levasseur

  There is another similar question to mine, but the discussion veered away from the problem I'm encounting. Say I have a system that deals with expense reports (ER). You can create and edit them, add attachments, and approve/reject them. An expense report might look like this: GET /er/1 => {"title": "Trip to NY", "totalcost": "400 USD", "comments": [ "john: Please add the total cost", "mike: done, can you approve it now?" ], "approvals": [ {"john": "Pending"}, {"finance-group": "Pending"}] } That looks fine, right? Thats what an expense report document looks like. If you want to update it, you can do this: POST /er/1 {"title": "Trip to NY 2010"} If you want to approve it, you can do this: POST /er/1/approval {"approved": true} But, what if you want to update the report and approve it at the same time? How do we do that? If you only wanted to approve, then doing a POST to something like /er/1/approval makes sense. We could put a flag in the URL, POST /er/1?approve=1, and send the data changes as the body, but that flag doesn't seem RESTful. We could put special field to be submitted, too, but that seems a bit hacky, too. If we did that, then why not send up data with attributes like set_title or add_to_cost? We could create a new resource for updating and approving, but (1) I can't think of how to name it without verbs, and (2) it doesn't seem right to name a resource based on what actions can be done to it (what happens if we add more actions?) We could have an X-Approve: True|False header, but headers seem like the wrong tool for the job. It'd also be difficult to get set headers without using javascript in a browser. We could use a custom media-type, application/approve+yes, but that seems no better than creating a new resource. We could create a temporary "batch operations" url, /er/1/batch/A. The client then sends multiple requests, perhaps POST /er/1/batch/A to update, then POST /er/1/batch/A/approval to approve, then POST /er/1/batch/A/status to end the batch. On the backend, the server queues up all the batch requests somewhere, then processes them in the same backend-transaction when it receives the "end batch processing" request. The downside with this is, obviously, that it introduces a lot of complexity. So, what is a good, general way to solve the problem of performing multiple actions in a single request? General because its easy to imagine additional actions that might be done in the same request: Suppress or send notifications (to email, chat, another system, whatever) Override some validation (maximum cost, names of dinner attendees) Trigger backend workflow that doesn't have a representation in the document.

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• How would you organize this Javascript?

  - by Anurag

  How do you usually organize complex web applications that are extremely rich on the client side. I have created a contrived example to indicate the kind of mess it's easy to get into if things are not managed well for big apps. Feel free to modify/extend this example as you wish - http://jsfiddle.net/NHyLC/1/ The example basically mirrors part of the comment posting on SO, and follows the following rules: Must have 15 characters minimum, after multiple spaces are trimmed out to one. If Add Comment is clicked, but the size is less than 15 after removing multiple spaces, then show a popup with the error. Indicate amount of characters remaining and summarize with color coding. Gray indicates a small comment, brown indicates a medium comment, orange a large comment, and red a comment overflow. One comment can only be submitted every 15 seconds. If comment is submitted too soon, show a popup with appropriate error message. A couple of issues I noticed with this example. This should ideally be a widget or some sort of packaged functionality. Things like a comment per 15 seconds, and minimum 15 character comment belong to some application wide policies rather than being embedded inside each widget. Too many hard-coded values. No code organization. Model, Views, Controllers are all bundled together. Not that MVC is the only approach for organizing rich client side web applications, but there is none in this example. How would you go about cleaning this up? Applying a little MVC/MVP along the way? Here's some of the relevant functions, but it will make more sense if you saw the entire code on jsfiddle: /** * Handle comment change. * Update character count. * Indicate progress */ function handleCommentUpdate(comment) { var status = $('.comment-status'); status.text(getStatusText(comment)); status.removeClass('mild spicy hot sizzling'); status.addClass(getStatusClass(comment)); } /** * Is the comment valid for submission */ function commentSubmittable(comment) { var notTooSoon = !isTooSoon(); var notEmpty = !isEmpty(comment); var hasEnoughCharacters = !isTooShort(comment); return notTooSoon && notEmpty && hasEnoughCharacters; } // submit comment $('.add-comment').click(function() { var comment = $('.comment-box').val(); // submit comment, fake ajax call if(commentSubmittable(comment)) { .. } // show a popup if comment is mostly spaces if(isTooShort(comment)) { if(comment.length < 15) { // blink status message } else { popup("Comment must be at least 15 characters in length."); } } // show a popup is comment submitted too soon else if(isTooSoon()) { popup("Only 1 comment allowed per 15 seconds."); } });

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• Evaluating points in time by months, but without referencing years in Rails

  - by MikeH

  FYI, There is some overlap in the initial description of this question with a question I asked yesterday, but the question is different. My app has users who have seasonal products. When a user selects a product, we allow him to also select the product's season. We accomplish this by letting him select a start date and an end date for each product. We're using date_select to generate two sets of drop-downs: one for the start date and one for the end date. Including years doesn't make sense for our model. So we're using the option: discard_year => true When you use discard_year => true, Rails sets a year in the database, it just doesn't appear in the views. Rails sets all the years to either 0001 or 0002 in our app. Yes, we could make it 2009 and 2010 or any other pair. But the point is that we want the months and days to function independent of a particular year. If we used 2009 and 2010, then those dates would be wrong next year because we don't expect these records to be updated every year. My problem is that we need to dynamically evaluate the availability of products based on their relationship to the current month. For example, assume it's March 15. Regardless of the year, I need a method that can tell me that a product available from October to January is not available right now. If we were using actual years, this would be pretty easy. For example, in the products model, I can do this: def is_available? (season_start.past? && season_end.future?) end I can also evaluate a start_date and an end_date against current_date However, in setup I've described above where we have arbitrary years that only make sense relative to each other, these methods don't work. For example, is_available? would return false for all my products because their end date is in the year 0001 or 0002. What I need is a method just like the ones I used as examples above, except that they evaluate against current_month instead of current_date, and past? and future months instead of years. I have no idea how to do this or whether Rails has any built in functionality that could help. I've gone through all the date and time methods/helpers in the API docs, but I'm not seeing anything equivalent to what I'm describing. Thanks.

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• WinRT ControlTemplate ItemsPanel

  - by user1427149

  I'm new to WinRT and am trying to create a standard gridview which has a group heading with a number of tiles beneath it. That bit is easy. I'm trying to modify it so that beneath the grid of tiles I can also add a footer using the containers style: <GridView x:Name="itemGridView" AutomationProperties.AutomationId="ItemGridView" AutomationProperties.Name="Grouped Items" Margin="116,0,40,46" ItemsSource="{Binding Source={StaticResource groupedItemsViewSource}}" ItemTemplate="{StaticResource Project200x200ItemTemplate}" SelectionMode="None" IsItemClickEnabled="True" ItemClick="ItemView_ItemClick"> <GridView.ItemsPanel> <ItemsPanelTemplate> <VirtualizingStackPanel Orientation="Horizontal"/> </ItemsPanelTemplate> </GridView.ItemsPanel> <GridView.GroupStyle> <GroupStyle> <GroupStyle.HeaderTemplate> <DataTemplate> <Grid Margin="1,0,0,6"> <Button AutomationProperties.Name="Group Title" Content="{Binding Name}" Click="Header_Click" Style="{StaticResource TextButtonStyle}" FontWeight="{Binding IsSelected, ConverterParameter=FontWeight, Converter={StaticResource BooleanToFontWeightConverter}}" /> </Grid> </DataTemplate> </GroupStyle.HeaderTemplate> <GroupStyle.Panel> <ItemsPanelTemplate> <VariableSizedWrapGrid Background="Red" Orientation="Vertical" Margin="0,0,40,0" /> </ItemsPanelTemplate> </GroupStyle.Panel> <GroupStyle.ContainerStyle> <Style TargetType="GroupItem"> <Setter Property="Template"> <Setter.Value> <ControlTemplate> <StackPanel> <ContentPresenter/> <ItemsPresenter/> <TextBlock Text="*** End of group ***"/> </StackPanel> </ControlTemplate> </Setter.Value> </Setter> </Style> </GroupStyle.ContainerStyle> </GroupStyle> </GridView.GroupStyle> </GridView> This almost works but after adding the container style, the grid of tiles no longer shows... the group header and 'End of group' textblock is showing, but I've lost the tile grid. Can anyone spot what I'm doing wrong...?

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• QT vs. Net - REAL comparisons for R.A.D. projects

  - by Pirate for Profit

  Man in all these Qt vs. .NET discussions 90% these people argue about the dumbest crap. Trying to get a real comparison chart here, because I know a little about both frameworks but I don't know everything. I believe Qt and .NET both have strengths and weaknesses. This is to make a comparison that highlights these so people can make more informed decisions before embarking on a project, in the spirit of R.A.D. Event Handling In Qt the event handling system is very simple. You just emit signals when something cool happens and then catch them in slots. ie. // run some calculations, then emit valueChanged(30, false, 20.2); and then catching it, any object can make a slot to recieve that message easily void MyObj::valueChanged(int percent, bool ok, float timeRemaining). It's easy to "block" an event or "disconnect" when needed, and works seamlessly across threads... once you get the hang of it, it just seems a lot more natural and intuitive than the way the .NET event handling is set up (you know, void valueChanged(object sender, CustomEventArgs e). And I'm not just talking about syntax, because in the end the .NET anonymous delegates are the bomb. I'm also talking about in more than just reflection (because, yes, .NET obviously has much stronger reflection capabilities). I'm talking about in the way the system feels to a human being. Qt wins hands down for the simplest yet still flexible event handling system ever i m o. Plugins and such I do love some of the ease of C# compared to C++, as well as .NET's assembly architecture, even though it leads to a bunch of .dll's (there's ways to combine everything into a single exe though). That is a big bonus for modular projects, which are a PITA to import stuff in C++ as far as RAD is concerned. Database Ease of Doing Crap Also what about datasets and database manipulations. I think .net wins here but I'm not sure. Threading/Conccurency How do you guys think of the threading? In .NET, all I've ever done is make like a list of master worker threads with locks. I like QConcurrentFramework, you don't worry about locks or anything, and with the ease of the signal slot system across threads it's nice to get notified about the progress of things. QConcurrent is the simplest threading mechanism I've ever played with. Memory Usage Also what do you think of the overall memory usage comparison. Is the .NET garbage collector pretty on the ball and quick compared to the instantaneous nature of native memory management? Or does it just let programs leak up a storm and lag the computer then clean it up when it's about to really lag? Doesn't the just-in-time compiler make native code that is pretty good, like and that only happens the first time the program is run? However, I am a n00b who doesn't know what I'm talking about, please school me on the subject.

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• MySQL table organization and optimization (Rails)

  - by aguynamedloren

  I've been learning Ruby on Rails over the past few months with no prior programming experience. Lately, I've been thinking about database optimization and table organization. I know there are great books on the subject, but I typically learn by example / as I go. Here's a hypothetical situation: Let's say I am building a social network for a niche community with 250,000 members (users). The users have the ability to attend events. Let's say there are 50,000 past/present/future events. Much like Facebook events, a user can attend any number of events and an event can have any number of attendees. In the database, there would be a table for users and a table for events. Somehow I would have to create an association between the users and events. I could create an "events" column in the users table such that each user row would contain a hash of event IDs, or I could create an "attendees" column in the events table such that each event row would contain a hash of user IDs. Neither of these solutions seem ideal, however. On a users profile page, I want to display the list of events they are associated with, which would require scanning the 50,000 event rows for the user ID of said user if I include an "attendees" column in the events table. Likewise, on an event page, I want to display a list of attendees for the event, which would require scanning the 250,000 user rows for the event ID of said event if I include an "events" column in the users table. Option 3 would be to create a third table that contains the attendee information for each and every event - but I don't see how this would solve any problems. Are these non-issues? Rails makes accessing all of this information easy, but I guess I'm worried about scale. It is entirely possible that I am under-estimating the speed and processing power of modern databases / servers / etc. How long would it take to scan 250,000 user rows for specific event IDs - 10ms? 100ms? 1,000ms? I guess that's not that bad. Am I just over-thinking this?

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• Another IKImageView Question: copying a region

  - by Brian Postow

  I'm trying to use the select and copy feature of the IKImageView. If all you want to do is have an app with an image, select a portion and copy it to the clipboard, it's easy. You set the copy menu pick to the first responder's copy:(id) method and magically everything works. However, if you want something more complicated, like you want to copy as part of some other operation, I can't seem to find the method to do this. IKImageView doesn't seem to have a copy method, it doesn't seem to have a method that will even tell you the selected rectangle! I have gone through Hillegass' book, so I understand how the clipboard works, just not how to get the portion of the image out of the view... Now, I'm starting to think that I made a mistake in basing my project on IKImageView, but it's what Preview is built on (or so I've read), so I figured it had to be stable... and anyway, now it's too late, I'm too deep in this to start over... So, other than not using IKImageView, any suggestions on how to copy the select region to the clipboard manually? EDIT actually, I have found the copy(id) method, but when I call it, I get <Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 16 bits/pixel; 1-component color space; kCGImageAlphaPremultipliedLast; 2624 bytes/row. Which obviously doesn't happen when I do a normal copy through the first-responder... I understand the error message, but I'm not sure where it's getting those parameters from... Is there any way to trace through this and see how this is happening? A debugger won't help for obvious reasons, as well as the fact that I'm doing this in Mozilla, so a debugger isn't an option anyway... EDIT 2 It occurs to me that the copy:(id) method I found may be copying the VIEW rather than copying a chunk of the image to the clipboard, which is what I need. The reason I thought it was the clipboard copy is that in another project, where I'm copying from an IKImageView to the clipboard straight from the edit menu, it just sends a copy:(id) to the firstResponder, but I'm not actually sure what the firstresponder does with it...

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• LINQ aggregate left join on SQL CE

  - by P Daddy

  What I need is such a simple, easy query, it blows me away how much work I've done just trying to do it in LINQ. In T-SQL, it would be: SELECT I.InvoiceID, I.CustomerID, I.Amount AS AmountInvoiced, I.Date AS InvoiceDate, ISNULL(SUM(P.Amount), 0) AS AmountPaid, I.Amount - ISNULL(SUM(P.Amount), 0) AS AmountDue FROM Invoices I LEFT JOIN Payments P ON I.InvoiceID = P.InvoiceID WHERE I.Date between @start and @end GROUP BY I.InvoiceID, I.CustomerID, I.Amount, I.Date ORDER BY AmountDue DESC The best equivalent LINQ expression I've come up with, took me much longer to do: var invoices = ( from I in Invoices where I.Date >= start && I.Date <= end join P in Payments on I.InvoiceID equals P.InvoiceID into payments select new{ I.InvoiceID, I.CustomerID, AmountInvoiced = I.Amount, InvoiceDate = I.Date, AmountPaid = ((decimal?)payments.Select(P=>P.Amount).Sum()).GetValueOrDefault(), AmountDue = I.Amount - ((decimal?)payments.Select(P=>P.Amount).Sum()).GetValueOrDefault() } ).OrderByDescending(row=>row.AmountDue); This gets an equivalent result set when run against SQL Server. Using a SQL CE database, however, changes things. The T-SQL stays almost the same. I only have to change ISNULL to COALESCE. Using the same LINQ expression, however, results in an error: There was an error parsing the query. [ Token line number = 4, Token line offset = 9,Token in error = SELECT ] So we look at the generated SQL code: SELECT [t3].[InvoiceID], [t3].[CustomerID], [t3].[Amount] AS [AmountInvoiced], [t3].[Date] AS [InvoiceDate], [t3].[value] AS [AmountPaid], [t3].[value2] AS [AmountDue] FROM ( SELECT [t0].[InvoiceID], [t0].[CustomerID], [t0].[Amount], [t0].[Date], COALESCE(( SELECT SUM([t1].[Amount]) FROM [Payments] AS [t1] WHERE [t0].[InvoiceID] = [t1].[InvoiceID] ),0) AS [value], [t0].[Amount] - (COALESCE(( SELECT SUM([t2].[Amount]) FROM [Payments] AS [t2] WHERE [t0].[InvoiceID] = [t2].[InvoiceID] ),0)) AS [value2] FROM [Invoices] AS [t0] ) AS [t3] WHERE ([t3].[Date] >= @p0) AND ([t3].[Date] <= @p1) ORDER BY [t3].[value2] DESC Ugh! Okay, so it's ugly and inefficient when run against SQL Server, but we're not supposed to care, since it's supposed to be quicker to write, and the performance difference shouldn't be that large. But it just doesn't work against SQL CE, which apparently doesn't support subqueries within the SELECT list. In fact, I've tried several different left join queries in LINQ, and they all seem to have the same problem. Even: from I in Invoices join P in Payments on I.InvoiceID equals P.InvoiceID into payments select new{I, payments} generates: SELECT [t0].[InvoiceID], [t0].[CustomerID], [t0].[Amount], [t0].[Date], [t1].[InvoiceID] AS [InvoiceID2], [t1].[Amount] AS [Amount2], [t1].[Date] AS [Date2], ( SELECT COUNT(*) FROM [Payments] AS [t2] WHERE [t0].[InvoiceID] = [t2].[InvoiceID] ) AS [value] FROM [Invoices] AS [t0] LEFT OUTER JOIN [Payments] AS [t1] ON [t0].[InvoiceID] = [t1].[InvoiceID] ORDER BY [t0].[InvoiceID] which also results in the error: There was an error parsing the query. [ Token line number = 2, Token line offset = 5,Token in error = SELECT ] So how can I do a simple left join on a SQL CE database using LINQ? Am I wasting my time?

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• design for a wrapper around command-line utilities

  - by hatchetman82

  im trying to come up with a design for a wrapper for use when invoking command line utilities in java. the trouble with runtime.exec() is that you need to keep reading from the process' out and err streams or it hangs when it fills its buffers. this has led me to the following design: public class CommandLineInterface { private final Thread stdOutThread; private final Thread stdErrThread; private final OutputStreamWriter stdin; private final History history; public CommandLineInterface(String command) throws IOException { this.history = new History(); this.history.addEntry(new HistoryEntry(EntryTypeEnum.INPUT, command)); Process process = Runtime.getRuntime().exec(command); stdin = new OutputStreamWriter(process.getOutputStream()); stdOutThread = new Thread(new Leech(process.getInputStream(), history, EntryTypeEnum.OUTPUT)); stdOutThread.setDaemon(true); stdOutThread.start(); stdErrThread = new Thread(new Leech(process.getErrorStream(), history, EntryTypeEnum.ERROR)); stdErrThread.setDaemon(true); stdErrThread.start(); } public void write(String input) throws IOException { this.history.addEntry(new HistoryEntry(EntryTypeEnum.INPUT, input)); stdin.write(input); stdin.write("\n"); stdin.flush(); } } public class Leech implements Runnable{ private final InputStream stream; private final History history; private final EntryTypeEnum type; private volatile boolean alive = true; public Leech(InputStream stream, History history, EntryTypeEnum type) { this.stream = stream; this.history = history; this.type = type; } public void run() { BufferedReader reader = new BufferedReader(new InputStreamReader(stream)); String line; try { while(alive) { line = reader.readLine(); if (line==null) break; history.addEntry(new HistoryEntry(type, line)); } } catch (Exception e) { e.printStackTrace(); } } } my issue is with the Leech class (used to "leech" the process' out and err streams and feed them into history - which acts like a log file) - on the one hand reading whole lines is nice and easy (and what im currently doing), but it means i miss the last line (usually the prompt line). i only see the prompt line when executing the next command (because there's no line break until that point). on the other hand, if i read characters myself, how can i tell when the process is "done" ? (either complete or waiting for input) has anyone tried something like waiting 100 millis since the last output from the process and declaring it "done" ? any better ideas on how i can implement a nice wrapper around things like runtime.exec("cmd.exe") ?

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• Sening a file from memory (rather than disk) over HTTP using libcurl

  - by cinek1lol

  Hi! I would like to send pictures via a program written in C + +. - OK WinExec("C:\\curl\\curl.exe -H Expect: -F \"fileupload=@C:\\curl\\ok.jpg\" -F \"xml=yes\" -# \"http://www.imageshack.us/index.php\" -o data.txt -A \"Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1\" -e \"http://www.imageshack.us\"", NULL); It works, but I would like to send the pictures from pre-loaded carrier to a variable char (you know what I mean? First off, I load the pictures into a variable and then send the variable), cause now I have to specify the path of the picture on a disk. I wanted to write this program in c++ by using the curl library, not through exe. extension. I have also found such a program (which has been modified by me a bit) #include <stdio.h> #include <string.h> #include <iostream> #include <curl/curl.h> #include <curl/types.h> #include <curl/easy.h> int main(int argc, char *argv[]) { CURL *curl; CURLcode res; struct curl_httppost *formpost=NULL; struct curl_httppost *lastptr=NULL; struct curl_slist *headerlist=NULL; static const char buf[] = "Expect:"; curl_global_init(CURL_GLOBAL_ALL); /* Fill in the file upload field */ curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "send", CURLFORM_FILE, "nowy.jpg", CURLFORM_END); curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "nowy.jpg", CURLFORM_COPYCONTENTS, "nowy.jpg", CURLFORM_END); curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "submit", CURLFORM_COPYCONTENTS, "send", CURLFORM_END); curl = curl_easy_init(); headerlist = curl_slist_append(headerlist, buf); if(curl) { curl_easy_setopt(curl, CURLOPT_URL, "http://www.imageshack.us/index.php"); if ( (argc == 2) && (!strcmp(argv[1], "xml=yes")) ) curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerlist); curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost); res = curl_easy_perform(curl); curl_easy_cleanup(curl); curl_formfree(formpost); curl_slist_free_all (headerlist); } system("pause"); return 0; }

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• Saving a reference to a int.

  - by Scott Chamberlain

  Here is a much simplified version of what I am trying to do static void Main(string[] args) { int test = 0; int test2 = 0; Test A = new Test(ref test); Test B = new Test(ref test); Test C = new Test(ref test2); A.write(); //Writes 1 should write 1 B.write(); //Writes 1 should write 2 C.write(); //Writes 1 should write 1 Console.ReadLine(); } class Test { int _a; public Test(ref int a) { _a = a; //I loose the reference here } public void write() { var b = System.Threading.Interlocked.Increment(ref _a); Console.WriteLine(b); } } In my real code I have a int that will be incremented by many threads however where the threads a called it will not be easy to pass it the parameter that points it at the int(In the real code this is happening inside a IEnumerator). So a requirement is the reference must be made in the constructor. Also not all threads will be pointing at the same single base int so I can not use a global static int either. I know I can just box the int inside a class and pass the class around but I wanted to know if that is the correct way of doing something like this? What I think could be the correct way: static void Main(string[] args) { Holder holder = new Holder(0); Holder holder2 = new Holder(0); Test A = new Test(holder); Test B = new Test(holder); Test C = new Test(holder2); A.write(); //Writes 1 should write 1 B.write(); //Writes 2 should write 2 C.write(); //Writes 1 should write 1 Console.ReadLine(); } class Holder { public Holder(int i) { num = i; } public int num; } class Test { Holder _holder; public Test(Holder holder) { _holder = holder; } public void write() { var b = System.Threading.Interlocked.Increment(ref _holder.num); Console.WriteLine(b); } } Is there a better way than this?

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• Find location using only distance and range?

  - by pinnacler

  Triangulation works by checking your angle to three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and it's to my right at 90 degrees." Repeat 2 more times for different targets and angles. Trilateration works by checking your distance from three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and I'm 100 meters away from that." Repeat 2 more times for different targets and ranges. But both of those methods rely on knowing WHAT you're looking at. Say you're in a forest and you can't differentiate between trees, but you know where key trees are. These trees have been hand picked as "landmarks." You have a robot moving through that forest slowly. Do you know of any ways to determine location based solely off of angle and range, exploiting geometry between landmarks? Note, you will see other trees as well, so you won't know which trees are key trees. Ignore the fact that a target may be occluded. Our pre-algorithm takes care of that. 1) If this exists, what's it called? I can't find anything. 2) What do you think the odds are of having two identical location 'hits?' I imagine it's fairly rare. 3) If there are two identical location 'hits,' how can I determine my exact location after I move the robot next. (I assume the chances of having 2 occurrences of EXACT angles in a row, after I reposition the robot, would be statistically impossible, barring a forest growing in rows like corn). Would I just calculate the position again and hope for the best? Or would I somehow incorporate my previous position estimate into my next guess? If this exists, I'd like to read about it, and if not, develop it as a side project. I just don't have time to reinvent the wheel right now, nor have the time to implement this from scratch. So if it doesn't exist, I'll have to figure out another way to localize the robot since that's not the aim of this research, if it does, lets hope it's semi-easy.

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• Stack and queue operations on the same array.

  - by Passonate Learner

  Hi. I've been thinking about a program logic, but I cannot draw a conclusion to my problem. Here, I've implemented stack and queue operations to a fixed array. int A[1000]; int size=1000; int top; int front; int rear; bool StackIsEmpty() { return (top==0); } bool StackPush( int x ) { if ( top >= size ) return false; A[top++] = x; return true; } int StackTop( ) { return A[top-1]; } bool StackPop() { if ( top <= 0 ) return false; A[--top] = 0; return true; } bool QueueIsEmpty() { return (front==rear); } bool QueuePush( int x ) { if ( rear >= size ) return false; A[rear++] = x; return true; } int QueueFront( ) { return A[front]; } bool QueuePop() { if ( front >= rear ) return false; A[front++] = 0; return true; } It is presumed(or obvious) that the bottom of the stack and the front of the queue is pointing at the same location, and vice versa(top of the stack points the same location as rear of the queue). For example, integer 1 and 2 is inside an array in order of writing. And if I call StackPop(), the integer 2 will be popped out, and if I call QueuePop(), the integer 1 will be popped out. My problem is that I don't know what happens if I do both stack and queue operations on the same array. The example above is easy to work out, because there are only two values involved. But what if there are more than 2 values involved? For example, if I call StackPush(1); QueuePush(2); QueuePush(4); StackPop(); StackPush(5); QueuePop(); what values will be returned in the order of bottom(front) from the final array? I know that if I code a program, I would receive a quick answer. But the reason I'm asking this is because I want to hear a logical explanations from a human being, not a computer.

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• Issues in Ada Concurrency

  - by Arkapravo

  Hi I need some help and also some insight. This is a program in Ada-2005 which has 3 tasks. The output is 'z'. If the 3 tasks do not happen in the order of their placement in the program then output can vary from z = 2, z = 1 to z = 0 ( That is easy to see in the program, mutual exclusion is attempted to make sure output is z = 2). WITH Ada.Text_IO; USE Ada.Text_IO; WITH Ada.Integer_Text_IO; USE Ada.Integer_Text_IO; WITH System; USE System; procedure xyz is x : Integer := 0; y : Integer := 0; z : Integer := 0; task task1 is pragma Priority(System.Default_Priority + 3); end task1; task task2 is pragma Priority(System.Default_Priority + 2); end task2; task task3 is pragma Priority(System.Default_Priority + 1); end task3; task body task1 is begin x := x + 1; end task1; task body task2 is begin y := x + y; end task2; task body task3 is begin z := x + y + z; end task3; begin Put(" z = "); Put(z); end xyz; I first tried this program (a) without pragmas, the result : In 100 tries, occurence of 2: 86, occurence of 1: 10, occurence of 0: 4. Then (b) with pragmas, the result : In 100 tries, occurence of 2: 84, occurence of 1 : 14, occurence of 0: 2. Which is unexpected as the 2 results are nearly identical. Which means pragmas or no pragmas the output has same behavior. Those who are Ada concurrency Gurus please shed some light on this topic. Alternative solutions with semaphores (if possible) is also invited. Further in my opinion for a critical process (that is what we do with Ada), with pragmas the result should be z = 2, 100% at all times, hence or otherwise this program should be termed as 85% critical !!!! (That should not be so with Ada)

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• Help with iphone dev - beyond bounds error

  - by dusk

  I'm just learning iphone development, so please forgive me for what is probably a beginner error. I've searched around and haven't found anything specific to my problem, so hopefully it is an easy fix. The book has examples of building a table from data hard coded via an array. Unfortunately it never really tells you how to get data from a URL, so I've had to look that up and that is where my problems show up. When I debug in xcode, it seems like the count is correct, so I don't understand why it is going out of bounds? This is the error message: 2010-05-03 12:50:42.705 Simple Table[3310:20b] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (1) beyond bounds (0)' My URL returns the following string: first,second,third,fourth And here is the iphone code with the book's working example commented out #import "Simple_TableViewController.h" @implementation Simple_TableViewController @synthesize listData; - (void)viewDidLoad { /* //working code from book NSArray *array = [[NSArray alloc] initWithObjects:@"Sleepy", @"Sneezy", @"Bashful", @"Bashful", @"Happy", @"Doc", @"Grumpy", @"Thorin", @"Dorin", @"Norin", @"Ori", @"Balin", @"Dwalin", @"Fili", @"Kili", @"Oin", @"Gloin", @"Bifur", @"Bofur", @"Bombur", nil]; self.listData = array; [array release]; */ //code from interwebz that crashes NSString *urlstr = [[NSString alloc] initWithFormat:@"http://www.mysite.com/folder/iphone-test.php"]; NSURL *url = [[NSURL alloc] initWithString:urlstr]; NSString *ans = [NSString stringWithContentsOfURL:url]; NSArray *listItems = [ans componentsSeparatedByString:@","]; self.listData = listItems; [urlstr release]; [url release]; [ans release]; [listItems release]; [super viewDidLoad]; } - (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use. } - (void)viewDidUnload { // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; self.listData = nil; [super viewDidUnload]; } - (void)dealloc { [listData release]; [super dealloc]; } #pragma mark - #pragma mark Table View Data Source Methods - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [self.listData count]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *SimpleTableIdentifier = @"SimpleTableIdentifier"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:SimpleTableIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:SimpleTableIdentifier] autorelease]; } NSUInteger row = [indexPath row]; cell.textLabel.text = [listData objectAtIndex:row]; return cell; } @end

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• SaaS Architecture Question from Newbie

  - by user226767

  I have developed a number of departmental client-server applications, and am now ready to begin working on moving one of these applications to a SaaS model. I have done some basic web development, but I'm a newbie when it comes to SaaS architectures. One of the first questions that comes to mind as I try to design the architecture is the question of single vs. multi tenancy. The pros and cons of each vary significantly depending on the type of application and scale required, so I'd like to describe my application and scale needs below, and hope others can comment on how I should get started with the architecture. The client-server application currently consists of a Firebird database and a Windows application. The database contains about 20 tables containing a few thousand records in 4 primary tables, and a few hundred records in various lookup and related tables. Although the number of records is small, the size can get large, as the database can contain large BLOBS. Each customer sets up their own database and has a handful of users within the organization connected to it. When I update the db schema, a new windows application is released, and it checks the db schema and then applies the updates as needed. For the SaaS application, I am designing for 100's (not 1000's or millions) of new customers per year. My first thought was to go with a multi tenancy model to make updates easy (shut down apply the updates to one database, and then start up). On the other hand, a single tenancy model would provide a means to roll updates out to a group of customers at a time, and spread the risk of data corruption - i.e. if something goes wrong with a database, it will impact one customer instead of all customers. With this idea, I was thinking of having a single web front-end which would connect to a single customer database upon login. Thus, when a new customer creates an account, a new database would be created (each customer would have their own db with multiple users as needed for the customer). In this model, a db update would require either a process to go through each db to apply schema changes, or a trigger upon logging in to initiate a schema update similar to the client-server model currently in use. Can anyone point me to information for similar applications which have been ported from client-server to SaaS? Or provide any pointers to consider? Basically I'm looking for architecture examples of taking a departmental application and making it available as a self service website for multiple customers. Thanks for any suggestions, resources, etc.

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• In Rails, how should I implement a Status field for a Tasks app - integer or enum?

  - by Doug

  For a Rails 3.0 Todo app, I have a Tasks model with a Status field. What's the best way to store the Status field data (field type) and still display a human-readable version in a view (HTML table)? Status can be: 0 = Normal 1 = Active 2 = Completed Right now I have this: Rails Schema Here: create_table "tasks", :force = true do |t| t.integer "status", :limit = 1, :default = 0, :null = false Rails Model Here: class Task < ActiveRecord::Base validates_inclusion_of :status, :in => 0..2, :message => "{{value}} must be 0, 1, or 2" Rails View Here: <h1>Listing tasks</h1> <table> <tr> <th>Status</th> <th>Name</th> <th></th> <th></th> <th></th> </tr> <% @tasks.each do |task| %> <tr> <td><%= task.status %></td> <td><%= task.name %></td> <td><%= link_to 'Show', task %></td> <td><%= link_to 'Edit', edit_task_path(task) %></td> <td><%= link_to 'Delete', task, :confirm => 'Are you sure?', :method => :delete %></td> </tr> <% end %> </table> Requirements Store a Task's status in the db such that the values are easily localizable, i.e. I'm not sure I want to store "normal", "active", "completed" as a string field. Solution must work with Rails 3.0. Questions: Should I store the field as an integer (see above)? If so, how do I display the correct human readable status in an HTML table in my Rails view, e.g. show "Active" instead of "1" in the HTML table. Should I use an enum? If so, is this easy to localize later? Should I use straight strings, e.g. "Normal", "Active", "Completed" Can you provide a quick code sample of the view helper, controller or view code to make this work?

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• Change a UIButton View's background upon press

  - by Michael

  This should be easy but its got me stumped. I've got a button on each row of a table cell. The button is to delete the file associated with that row. I have an image that indicates if the file is present on the iPhone or not present. When the user presses the button, the target action method (showDeleteSheet) then calls a UIActionSheet with a variable to give it the indexPath of the row pressed. Then the user presses delete on the action sheet and the action sheet's clickedButtonAtIndex method deletes the file. Now, I need to update the button's background image property to change the image in the appropriate table cell to the not downloaded image. This can be done in either the button's target action method or the action sheet's clickedButtonAtIndex method. Here is some code: In the table's cellForRowAtIndexPath method I create the button: UIButton *deleteButton = [[UIButton buttonWithType:UIButtonTypeCustom] retain]; [deleteButton addTarget:self action:@selector(showDeleteSheet:) forControlEvents:UIControlEventTouchDown]; deleteButton.frame = CGRectMake(246, 26, 30, 30); if (![AppData isDownloaded:[dets objectForKey:@"fileName"]]) { [deleteButton setBackgroundImage:notdownloadedImage forState:UIControlStateNormal]; } else { [deleteButton setBackgroundImage:notdownloadedImage forState:UIControlStateNormal]; } In the button's target method: -(void)showDeleteSheet:(id)sender { //get the cell row that the button is in NSIndexPath *indexPath = [table indexPathForCell:(UITableViewCell *)[[sender superview] superview]]; NSInteger currentSection = indexPath.section; NSInteger currentIndexRow = indexPath.row; NSLog(@"section = %i row = %i", currentSection, currentIndexRow); UIButton *deleteButton = [UIButton buttonWithType:UIButtonTypeCustom]; [table reloadData]; //if deleteButton is declared in .h then the other instances of deleteButton show 'local declaration hides instance variable' [deleteButton setBackgroundImage:[UIImage imageNamed:@"not-downloaded.png"] forState:UIControlStateNormal]; UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:@"Delete this file?" delegate:self cancelButtonTitle:@"Cancel" destructiveButtonTitle:@"Delete" otherButtonTitles:nil]; actionSheet.tag = currentIndexRow; actionSheet.actionSheetStyle = UIActionSheetStyleDefault; [actionSheet showInView:self.view]; [actionSheet release]; } Perhaps the issue is that the call to [deleteButton setBackgroundImage...]; doesn't know which cell's button should be updated. If so I don't know how to tell it which. Because I test if the file is downloaded when the button is made and the background image is set, when I scroll down so the cell in question is de-queued then scroll back up it show's the correct image. I've tried to force the table to reload but [table reloadData]; is doing nothing. I've tried reloadRowsAtIndexPaths and still no good. Any one care to educate me on how this is done?

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• Why is it still so hard to write software?

  - by nornagon

  Writing software, I find, is composed of two parts: the Idea, and the Implementation. The Idea is about thinking: "I have this problem; how do I solve it?" and further, "how do I solve it elegantly?" The answers to these questions are obtainable by thinking about algorithms and architecture. The ideas come partially through analysis and partially through insight and intuition. The Idea is usually the easy part. You talk to your friends and co-workers and you nut it out in a meeting or over coffee. It takes an hour or two, plus revisions as you implement and find new problems. The Implementation phase of software development is so difficult that we joke about it. "Oh," we say, "the rest is a Simple Matter of Code." Because it should be simple, but it never is. We used to write our code on punch cards, and that was hard: mistakes were very difficult to spot, so we had to spend extra effort making sure every line was perfect. Then we had serial terminals: we could see all our code at once, search through it, organise it hierarchically and create things abstracted from raw machine code. First we had assemblers, one level up from machine code. Mnemonics freed us from remembering the machine code. Then we had compilers, which freed us from remembering the instructions. We had virtual machines, which let us step away from machine-specific details. And now we have advanced tools like Eclipse and Xcode that perform analysis on our code to help us write code faster and avoid common pitfalls. But writing code is still hard. Writing code is about understanding large, complex systems, and tools we have today simply don't go very far to help us with that. When I click "find all references" in Eclipse, I get a list of them at the bottom of the window. I click on one, and I'm torn away from what I was looking at, forced to context switch. Java architecture is usually several levels deep, so I have to switch and switch and switch until I find what I'm really looking for -- by which time I've forgotten where I came from. And I do that all day until I've understood a system. It's taxing mentally, and Eclipse doesn't do much that couldn't be done in 1985 with grep, except eat hundreds of megs of RAM. Writing code has barely changed since we were staring at amber on black. We have the theoretical groundwork for much more advanced tools, tools that actually work to help us comprehend and extend the complex systems we work with every day. So why is writing code still so hard?

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• Dealing with missing messages in JavaScript when using BOSH

  - by JamieD

  We recently went into private beta on our flagship product and had a small launch event. Unfortunately the venue had a terrible wireless connection and packets were being dropped left right and centre causing havoc with out system, basically it wasn't able to work at all! Luckily we were able to switch to a different network and rescue the demo. This highlighted something that I knew was already an issue but hadn't appreciated quite how much of an issue it could be. Our system relies heavily on BOSH and has a rather large JavaScript code base which now works rather well under good network conditions. However we need to make it work well under bad network conditions as well. Due to the way that XMPP works, a fire and forget system, it's not easy to tell if a message you sent, or were supposed to receive, was actually sent or received. For instance, we have an offer system, one user will send an offer to another over BOSH. When this message is received by the server a message is published to the offering users offers_sent PEP node and a similar message to the receiving users offers_received PEP node. While the sending user is able to tell if their offer was send (relatively) easily, if the notification to the receiving user is never received that user will never know it missed a message. A little about out JavaScript setup, it has 4 main layers: StropheJS An MVC framework for dealing with low level tasks and to build on top of An application layer which contains the app logic routes, controllers models etc. as well as a browser cache of the model data A UI layer that receives events and publishes events to and from the application layer One way to solve the missing messages issue would be to periodically check the PEP nodes for new data that the browser doesn't know about. If a new message was discovered the browsers cache would be invalidated and all new data would be requested from the server. I'm not sure this is the best way to go and it also doesn't cover all situations. We certainly don't want to get into the situation where we are sending messages to confirm the previous message was received at it's destination as this would double the network traffic. With the number of real time websites growing daily this is an issue that must have been encountered by other developers, it would be interesting to see how it's been solved by others. As far as I can see there are two situations in which messages go missing: On poor connections messages are not sent or received due to the packets being dropped Involving navigating between pages, a message is received by the browser but is not fully processed and stored in the local cache before the page is unloaded. Or a message is added to the send queue but never sent before the page is unloaded I suspect the hardest issue to solve will be number 2. Any thoughts on the subject would be much appreciated.

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