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• Should I use formal methods on my software project?

  - by Michael

  Our client wants us to build a web-based, rich internet application for gathering software requirements. Basically it's a web-based case tool that follows a specific process for getting requirements from stakeholders. I'm the project manager and we're still in the early phases of the project. I've been thinking about using formal methods to help clarify the requirements for the tool for both my client and the developers. By formal methods I mean some form of modeling, possibly something mathematically-based. Some of the things I've read about and are considering include Z (http://en.wikipedia.org/wiki/Z_notation), state machines, UML 2.0 (possibly with extensions such as OCL), Petri nets, and some coding-level stuff like contracts and pre and post conditions. Is there anything else I should consider? The developers are experienced but depending on the formalism used they may have to learn some math. I'm trying to determine whether it's worth while for me to use formal methods on this project and if so, to what extent. I know "it depends" so the most helpful answers for me is a yes/no and supporting arguments. Would you use formal methods if you were on this project?

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• Messaging pattern question

  - by Al Bundy

  Process A is calculating values for objects a1, a2, a3 etc. and is sending results to the middleware queue (RabbitMQ). Consumers read the queue and process these results further. Periodically process A has to send a snapshot of these values, so consumers could do some other calculations. Values for these objects might change independently. The queue might look like this a1, a1, a2, a1, a2, a2, a3... Consumers process each item in the queue. The snapshot has to contain all objects and consumers will process this message for all objects in one go. So the requirement is to have a queue like this: a1, a1, a3, a2, a2, [snapshot, a1, a2, a3], a3, a1 ... The problem is that these items are of different types: one type for objects like a1, a2 and other for a snapshot. This means that they should be processed in a diferent queues, but in that case there is a race condition: consumers might process objects before processing a snapshot. Is there any pattern to solve this (quite common) problem? We are using RabbitMQ for message queueing.

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• How do I exclude data from local table schema_migrations from being pushed to Heroku DB?

  - by Thierry Lam

  I was able to push my Ruby on Rails app with MySQL(local dev) to the Heroku server along with migrating my model with the command heroku rake db:migrate. I have also read the documentation on Database Import/Export. Is that doc referring to pushing actual data from my local dev DB to whichever Heroku's DB? Do I need to modify anything in the file database.yml to make it happen? I ran the following command: heroku db:push and I am getting the error: Sending data 2 tables, 3 records !!! Caught Server Exception | ETA: --:--:-- Taps Server Error: PGError ERROR: duplicate key value violates unique constraint "unique_schema_migrations" I have 2 tables, one I create for my app and the other schema_migrations. The total number of entries among the 2 tables is 3. I'm also printing the number of entries I have in the table I have created and it's showing 0. Any ideas what I might be missing or what I am doing wrong? EDIT: I figured out the above, Heroku's DB already have schema_migrations the moment I ran migrate. New question: Does anyone know how I can exclude data from a specific table from being pushed to Heroku DB. The table to exclude in this case will be schema_migrations. Not so good solution: I googled around and someone else was having the same issue. He suggested naming the schema_migrations table to zschema_migrations. In this way data from the other tables will be pushed properly until it fails on the last table. It's a pretty bad solution but will do for the time being. A better solution will be to use an existing Rails command which can reset a specific table from a database. I don't think Rake can do that.

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• Set the selected item for a combobox in a datagrid

  - by JingJingTao

  I am using a datagrid which has many combobox fields in it, when I click the datagrid combobox the selected item or highlighted value is the last item in the list, but I would like it to highlight the first(top) item in the list. I know for just a combobox, all I need to do is change the combobox.selecteditem or combobox.selectedindex, but I'm not sure what to do in this case. I have binded the combobox to a table in the database and used a datatable to store the combobox values and then I add a row to the datatable, I think the reason the last item in the combobox is highlighted is because I added a row to the datatable. Thank you for your help. String strGetTypes = "SELECT holidaycodeVARCHAR4Pk, codedescVARCHAR45 FROM holidaytype ORDER BY holidaycodeVARCHAR4Pk Desc"; DataTable dtHolidayType = new DataTable(); MySqlDataAdapter dbaElements = new MySqlDataAdapter(strGetTypes, ShareSqlSettings.dbConnect); dbaElements.Fill(dtHolidayType); DataGridViewComboBoxCell cboxDays = new DataGridViewComboBoxCell(); cboxDays.DataSource = dtHolidayType; cboxDays.DisplayMember = "codedescVARCHAR45"; cboxDays.ValueMember = "holidaycodeVARCHAR4Pk"; //Blank row dtHolidayType.Rows.Add(1); // gridDailyEmp.Rows[j].Cells[day] = cboxDays;

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• CheckBox won't toggle in Android ListView with focusable="false"

  - by user3563124

  I'm creating a ListView with a custom Adapter for displaying my entries. Each row contains a checkbox, and my adapter contains the following code: CheckBox cb = (CheckBox) v.findViewById(R.id.item_sold); cb.setChecked(p.isSold); setupCheckboxListener(cb, v, position); ... private void setupCheckboxListener(CheckBox check, final View v, final int position) { check.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { CheckBox cb = (CheckBox) v; if (cb.isChecked()) { System.out.println("Should become false!"); cb.setChecked(false); } else { System.out.println("Should become true!"); cb.setChecked(true); } } }); My row XML file includes the following: <CheckBox android:id="@+id/item_sold" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="0.10" android:layout_gravity="center" android:gravity="center" android:focusable="false" android:clickable="false"/> But anytime I press one of the checkboxes, check.isChecked() returns true, even if the box is unchecked. I even checked to make sure that the checkboxes were distinct and weren't picking up just the last value/etc. Setting up the listeners inline instead of in a method doesn't seem to help, either. It's literally just the isChecked() condition that isn't working appropriately - it seems to always give me the inverse value. Setting an onClick on the row is not acceptable in this case because I need to allow row selection for something else. What could be causing this issue?

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• What's wrong with debugging in Eclipse on Android?

  - by Sebastian Dwornik

  I've obviously been spoiled by Visual Studio, because although I'm just learning Android and the Eclipse environment, debugging apps in Eclipse is becoming a serious detriment to further development. For example, Eclipse will compile this divide by zero just fine: public class Lesson2Main extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate (savedInstanceState); int i = 1 / 0; TextView tv = new TextView (this); tv.setText ("Hello, Android!"); setContentView (tv); } } And then, when it executes it under the debugger, I will get a full screen of useless debug info, non of which actually points me to the specific line containing the error. The stackTrace is null within the exception ('e') info tree, and it simply states a message stating 'ArithmeticException'. (that's nice, how about you point me in the direction of where you found it!?) I've looked all over the screen and am baffled that this IDE can't get this right. Does developing with Eclipse resort everyone back to 1991 with printf() like logging at every interval then to track down bugs? Seriously. Is there a configuration or plug-in that I'm missing to help with this? I haven't tested this case with XCode, but if the iPhone dev. IDE handles this more like Visual Studio, then no wonder the Android marketplace has so few apps. I'm excited about Android, but it seems that Eclipse is getting in the way.

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• How can I make a Maybe-Transformer MaybeT into an instance of MonadWriter?

  - by martingw

  I am trying to build a MaybeT-Transformer Monad, based on the example in the Real World Haskell, Chapter Monad Transformers: data MaybeT m a = MaybeT { runMT :: m (Maybe a) } instance (Monad m) => Monad (MaybeT m) where m >>= f = MaybeT $ do a <- runMT m case a of Just x -> runMT (f x) Nothing -> return Nothing return a = MaybeT $ return (Just a) instance MonadTrans MaybeT where lift m = MaybeT $ do a <- m return (Just a) This works fine, but now I want to make MaybeT an instance of MonadWriter: instance (MonadWriter w m) => MonadWriter w (MaybeT m) where tell = lift . tell listen m = MaybeT $ do unwrapped <- listen (runMT m) return (Just unwrapped) The tell is ok, but I can't get the listen function right. The best I could come up with after 1 1/2 days of constructor origami is the one you see above: unwrapped is supposed to be a tuple of (Maybe a, w), and that I want to wrap up in a Maybe-Type and put the whole thing in an empty MonadWriter. But the compiler complains with: Occurs check: cannot construct the infinite type: a = Maybe a When generalising the type(s) for `listen' In the instance declaration for `MonadWriter w (MaybeT m)' What am I missing?

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• Qt/MFC Migration Framework tool: properly exiting DLL?

  - by User

  I'm using the Qt/MFC Migration Framework tool following this example: http://doc.qt.nokia.com/solutions/4/qtwinmigrate/winmigrate-qt-dll-example.html The dll I build is loaded by a 3rd party MFC-based application. The 3rd party app basically calls one of my exported DLL functions to startup my plugin and another function to shutdown my application. Currently I'm doing nothing in my shutdown function. When I load my DLL in the 3rd party app the startup function is called and my DLL starts successfully and I can see my message box. However if I shutdown my plugin and then try to start it again I get the following error: Debug Error! Program: <my 3rd party app> Module: 4.7.1 File: global\qglobal.cpp Line: 2262 ASSERT failure in QWidget: "Widgets must be created in the GUI thread.", file kernel\qwidget.cpp line 1233 (Press Retry to debug the application) Abort Retry Ignore This makes me think I'm not doing something to properly shutdown my plugin. What do I need to do to shut it down properly? UPDATE: http://doc.qt.nokia.com/solutions/4/qtwinmigrate/winmigrate-walkthrough.html says: The DLL also has to make sure that it can be loaded together with other Qt based DLLs in the same process (in which case a QApplication object will probably exist already), and that the DLL that creates the QApplication object remains loaded in memory to avoid other DLLs using memory that is no longer available to the process. So I wonder if there is some problem where I need to somehow keep the original DLL loaded no matter what?

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• Email as a view.

  - by Hal

  I've been in some discussion recently about where email (notifications, etc...) should be sent in an ASP.NET MVC application. My nemesis grin argues that it only makes sense that the email should be sent from the controller. I argue that an email is simply an alternate or augmented view through a different channel. Much like I would download a file as the payload of an ActionResult, the email is simply delivered through a different protocol. I've worked an extension method that allows me to do the following: <% Html.RenderEmail(model.FromAddress, model.ToAddress, model.Subject); %> which I actually include within my the view that is displayed on the screen. The beauty is that, based on convention, if I call RenderEmail from a parent view named MyView.ascx, I attempt to render the contents of a view named MyViewEmail.ascx, unless it is not found, in which case I simply email a copy of parent view. It certainly does make it testable (I still have an ISMTPService injected for testing), I wondered if anyone had any thoughts on whether or not this breaks from good practice. In use it has been extremely handy when we needed to easily send an email or modify the contents of the emailed results vs the browser rendered results. Thanks, Hal

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• Performance question: Inverting an array of pointers in-place vs array of values

  - by Anders

  The background for asking this question is that I am solving a linearized equation system (Ax=b), where A is a matrix (typically of dimension less than 100x100) and x and b are vectors. I am using a direct method, meaning that I first invert A, then find the solution by x=A^(-1)b. This step is repated in an iterative process until convergence. The way I'm doing it now, using a matrix library (MTL4): For every iteration I copy all coeffiecients of A (values) in to the matrix object, then invert. This the easiest and safest option. Using an array of pointers instead: For my particular case, the coefficients of A happen to be updated between each iteration. These coefficients are stored in different variables (some are arrays, some are not). Would there be a potential for performance gain if I set up A as an array containing pointers to these coefficient variables, then inverting A in-place? The nice thing about the last option is that once I have set up the pointers in A before the first iteration, I would not need to copy any values between successive iterations. The values which are pointed to in A would automatically be updated between iterations. So the performance question boils down to this, as I see it: - The matrix inversion process takes roughly the same amount of time, assuming de-referencing of pointers is non-expensive. - The array of pointers does not need the extra memory for matrix A containing values. - The array of pointers option does not have to copy all NxN values of A between each iteration. - The values that are pointed to the array of pointers option are generally NOT ordered in memory. Hopefully, all values lie relatively close in memory, but *A[0][1] is generally not next to *A[0][0] etc. Any comments to this? Will the last remark affect performance negatively, thus weighing up for the positive performance effects?

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• Efficient method to calculate the rank vector of a list in Python

  - by Tamás

  I'm looking for an efficient way to calculate the rank vector of a list in Python, similar to R's rank function. In a simple list with no ties between the elements, element i of the rank vector of a list l should be x if and only if l[i] is the x-th element in the sorted list. This is simple so far, the following code snippet does the trick: def rank_simple(vector): return [rank for rank in sorted(range(n), key=vector.__getitem__)] Things get complicated, however, if the original list has ties (i.e. multiple elements with the same value). In that case, all the elements having the same value should have the same rank, which is the average of their ranks obtained using the naive method above. So, for instance, if I have [1, 2, 3, 3, 3, 4, 5], the naive ranking gives me [0, 1, 2, 3, 4, 5, 6], but what I would like to have is [0, 1, 3, 3, 3, 5, 6]. Which one would be the most efficient way to do this in Python? Footnote: I don't know if NumPy already has a method to achieve this or not; if it does, please let me know, but I would be interested in a pure Python solution anyway as I'm developing a tool which should work without NumPy as well.

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• How to Store State in Silverlight WCF RIA Services

  - by peter

  Hi All, I am developing a silverlight 3 application using WCF RIA services. I am using the AuthenticationBase class to handle my authentication. As I understand it under the hood this uses the ASP .NET authentication libraries. When I log into the site the authentication service handles login state so that if I close the site and open it straight away I am still logged in according to the server. When the webpage is refreshed or closed and reloaded I can call the method, WebContextBase.Current.Authentication.LoadUser() And it goes back to the authentication service (running on the server) and figures out whether I am still logged into the site. If a timeout has occured the answer will be no. If that is the case I can show a login dialog. The problem I want to solve is that the authentication service consumes the password, and there is no way I can ever retrieve that password again. If the user logs into the site I want to store the password on the server, and return a token to the client side to match up with that password. I have some other services on the server side that need that password. So where should I store that password on the server? How can that be done? How does the WCF authentication store state?

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• iPhone OS: Is there a way to set up KVO between two ManagedObject Entities?

  - by nickthedude

  I have 2 entities I want to link with KVO, one a single statTracker class that keeps track of different stats and the other an achievement class that contains information about achievements. Ideally what I want to be able to do is set up KVO by having an instance of the achievement class observe a value on the statTracker class and also set up a threshold value at which the achievement instance should be "triggered"(triggering in this case would mean showing a UIAlertView and changing a property on the achievement class.) I'd like to also set these relationships up on instantiation of the achievement class if possible so kind of like this: Achievement *achievement1 = (Achievement *)[NSEntityDescription insertNewObjectForEntityForName:@"Achievement" inManagedObjectContext:[[CoreDataSingleton sharedCoreDataSingleton] managedObjectContext]]; [achievement1 setAchievementName:@"2 time launcher"]; [achievement1 setAchievementDescription:@"So you've decided to come back for more eh? Here are some achievement points to get you going"]; [achievement1 setAchievementPoints:[NSNumber numberWithInt:300]; [achievement1 setObjectToObserve:@"statTrackerInstace" propertyToObserve:@"timesLaunched" valueOfPropertToSatisfyAchievement:2] Anyone out there know how I would set this up? Is there some way I could do this by way of relationships that I'm not seeing? Thanks, Nick

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• How to return proper 404 for google while providing user friendly content to the user?

  - by Marek

  I am bouncing between posting this here and on Superuser. Please excuse me if you feel this does not belong here. I am observing the behavior described here - Googlebot is requesting random urls on my site, like aecgeqfx.html or sutwjemebk.html. I am sure that I am not linking these urls from anywhere on my site. I suspect this may be google probing how we handle non existent content - to cite from an answer to the linked question: [google is requesting random urls to] see if your site correctly handles non-existent files (by returning a 404 response header) We have a custom page for nonexistent content - a styled page saying "Content not found, if you believe you got here by error, please contact us", with a few internal links, served (naturally) with a 200 OK. The URL is served directly (no redirection to a single url). I am afraid this may discriminate the site at google - they may not interpret the user friendly page as a 404 - not found and may think we are trying to fake something and provide duplicate content. How should I proceed to ensure that google will not think the site is bogus while providing user friendly message to users in case they click on dead links by accident?

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• Algorithm possible amounts (over)paid for a specific price, based on denominations

  - by Wrikken

  In a current project, people can order goods delivered to their door and choose 'pay on delivery' as a payment option. To make sure the delivery guy has enough change customers are asked to input the amount they will pay (e.g. delivery is 48,13, they will pay with 60,- (3*20,-)). Now, if it were up to me I'd make it a free field, but apparantly higher-ups have decided is should be a selection based on available denominations, without giving amounts that would result in a set of denominations which could be smaller. Example: denominations = [1,2,5,10,20,50] price = 78.12 possibilities: 79 (multitude of options), 80 (e.g. 4*20) 90 (e.g. 50+2*20) 100 (2*50) It's international, so the denominations could change, and the algorithm should be based on that list. The closest I have come which seems to work is this: for all denominations in reversed order (large=>small) add ceil(price/denomination) * denomination to possibles baseprice = floor(price/denomination) * denomination; for all smaller denominations as subdenomination in reversed order add baseprice + (ceil((price - baseprice) / subdenomination) * subdenomination) to possibles end for end for remove doubles sort Is seems to work, but this has emerged after wildly trying all kinds of compact algorithms, and I cannot defend why it works, which could lead to some edge-case / new countries getting wrong options, and it does generate some serious amounts of doubles. As this is probably not a new problem, and Google et al. could not provide me with an answer save for loads of pages calculating how to make exact change, I thought I'd ask SO: have you solved this problem before? Which algorithm? Any proof it will always work?

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• form layout in drupal from a module

  - by EricP

  I created my own module called "cssswitch". I'm trying to create my own html layout to display the admin form portion of the module. I understand how to use the hook_form_alter() to modify form elements, but I need to create the entire form layout to make some fields appear next to each other. It seems I need something like the way I have the frontend view of the node displayed with theme_cssswitch_display(), but for the admin part of the node. function cssswitch_form_alter(&$form, $form_state, $form_id) { switch($form_id) { case 'cssswitch_node_form': $form['hour_start']['#prefix'] = '<div class="start-box">'; $form['ampm_start']['#suffix'] = '</div>'; $form['ampm_start']['#attributes'] = array("style" => "border-width:2px;"); break; } } function cssswitch_theme() { return array( 'cssswitch_display' => array( 'arguments' => array('node'), ), ); } // to display the view of the node function theme_cssswitch_display($node) { $output = '<div class="cssswitch-cssfilename">Filename: '. check_plain($node->cssfilename). '</div>'; $output .= '<div class="cssswitch-time_start">Start: '. check_plain($node->hour_start). ':'.check_plain($node->minute_start).' '.check_plain($node->ampm_start).'</div>'; $output .= '<div class="cssswitch-time_end">End: '. check_plain($node->hour_end). ':'.check_plain($node->minute_end).' '.check_plain($node->ampm_end).'</div>'; return $output; } thanks for any help

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• Is there a way to make changes to toggles in my .emacs file apply without re-starting Emacs?

  - by Vivi

  I want to be able to make the changes to my .emacs file without having to reload Emacs. I found three questions which sort of answer what I am asking (you can find them here, here and here), but the problem is that the change I have just made is to a toggle, and as the comments to two of the answers (a1, a2) to those questions explain, the solutions given there (such as M-x reload-file or M-x eval-buffer) don't apply to toggles. I imagine there is a way of toggling the variable again with a command, but if there is a way to reload the whole .emacs and have the all the toggles re-evaluated without having to specify them, I would prefer. In any case, I would also appreciate if someone told me how to toggle the value of a variable so that if I just changed one toggle I can do it with a command rather than re-start Emacs just for that (I am new to Emacs). I don't know how useful this information is, but the change I applied was the following (which I got from this answer to another question): (setq skeleton-pair t) (setq skeleton-pair-on-word t) (global-set-key (kbd "[") 'skeleton-pair-insert-maybe) (global-set-key (kbd "(") 'skeleton-pair-insert-maybe) (global-set-key (kbd "{") 'skeleton-pair-insert-maybe) (global-set-key (kbd "<") 'skeleton-pair-insert-maybe) Edit: I included the above in .emacs and reloaded Emacs, so that the changes took effect. Then I commented all of it out and tried M-x load-file. This doesn't work. The suggestion below (C-x C-e by PP works if I am using it to evaluate the toggle first time, but not when I want to undo it). I would like something that would evaluate the commenting out, if such thing exists... Thanks :)

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• what kind of relationship is there between a common wall and the rooms that located next to it?

  - by siamak

  I want to know whats the Relationship between a common wall (that are located In an adjoining room ) and the rooms. As i know the relationship between a room and its walls is Composition not Aggregation (am i right ?) And according to the definition of Composition the contained object can't be shared between two containers, whereas in aggregation it is possible. now i am confused that whats the best modeling approach to represent the relationship between a common wall and the rooms located next to it ? It would be highly Appreciated if you could provide your advices with some code. |--------|--------| Approch1: (wall class ---- room class) /Composition Approach2: wall class ----- room class /Aggregation Approch3: we have a wall class and a Common wall class , Common wall class inherits from wall class adjoining room class ---- (1) Common wall class /Aggregation adjoining room class ---- (6) wall class / composition Approach4: I am a developer not a designer :) so this is my idea : class Room { private wall _firstwall ; private wall _secondtwall; private wall _thirdwall ; private wall _commonwall ; public Room( CommonWall commonwall) { _firstwall=new Wall(); _secondtwall=new Wall(); _thirdwall=new Wall(); _commonwall=commonwall; } } Class CommonWall:Wall { //... } // in somewher : static void main() { Wall _commonWall=new Wall(); Room room1=new Room(_commonWall); Room room2=new Room(_commonWall); Room [] adjacentRoom =new Room[2]{room1,room2}; } Edit 1: I think this is a clear question but just for more clarification : The point of the question is to find out whats the best pattern or approach to model a relationship for an object that is a component of two other objects in the same time. and about my example : waht i mean by a "room" ?,surely i mean an enclosed square room with 4 walls and one door.but in this case one of these walls is a common wall and is shared between two adjacent rooms.

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• UI Automation Button Style Enabled

  - by Victor Gaspar

  Hi, I'm evaluating UI Automation for UI testing for that I have a WPF application with the following button defined: <Button Style="{DynamicResource ButtonStyle}" x:Name="MyBtn"/> when I need to visually disable the button I just change the style so the user is aware that the button is disabled (the colour changed) but still the button is internally enabled so I can still launch the OnClick event in order to show a message when the user clicks on a "disabled" button. Now the problem is that I don't know how to check from UI Automation the Style that its currently applied i.e. if the button is disabled or enabled. Do you know how can I do that? In a normal situation I should do something like that: Automation.Condition cEBtn = new PropertyCondition(AutomationElement.AutomationIdProperty, "MyBtn"); AutomationElement mybtnElement = appRegraceElement.FindFirst(TreeScope.Children, cEBtn); bool disMyBtn = (bool)mybtnElement .GetCurrentPropertyValue(AutomationElement.IsEnabledProperty); but in my case the button is always enabled therefore I need to check the Style applied to the button. Thank you very much. Best regards

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• Link click does nothing after ajax switching?

  - by Neil

  An odd case I'm trying to figure out here. I'm trying to design a mailbox system, and making some of the options ajax-y. Here's the scenario: We have a page with 2 tabs, inbox and compose. Inbox is a essentially a list of links of the form mailbox.php?msg=xxx. Clicking on the inbox or compose tabs does an ajax switch. So, let's say we're on an message page: mailbox.php?msg=123 I click on "compose" - it ajax switches to a compose form. I change my mind, click on "inbox" - it goes back to a list of messages. Note, the url has not changed at this point (all has been done through ajax). I click on the same message as before. It should go back into that message. However, nothing happens! The url it should go to (mailbox.php?msg=123) IS the url showing in the address bar, but, due to the earlier ajax activity, it's showing the inbox. Thoughts on how to resolve this? And, out of curiosity, an explanation? Normally, clicking on a link that takes you to a page you're already on will reload the page. Thanks!

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• casting Collection<SomeClass> to Collection<SomeSuperClass>

  - by skrebbel

  Hi all, I'm sure this has been answered before, but I really cannot find it. I have a java class SomeClass and an abstract class SomeSuperClass. SomeClass extends SomeSuperClass. Another abstract method has a method that returns a Collection<SomeSuperClass>. In an implementation class, I have a Collection<SomeClass> myCollection I understand that I cannot just return myCollection, because Collection<SomeClass> does not inherit from Collection<SomeSuperClass>. Nevertheless, I know that everything in myCollection is a SomeSuperClass because after all, they're SomeClass objects which extend SomeSuperClass. How can I make this work? I.e. I want public class A { private Collection<SomeClass> myCollection; public Collection<SomeSuperClass> getCollection() { return myCollection; //compile error! } } The only way I've found is casting via a non-generic type and getting unchecked warnings and whatnot. There must be a more elegant way, though? I feel that also using Collections.checkedSet() and friends are not needed, since it is statically certain that the returned collection only contains SomeClass objects (this would not be the case when downcasting instead of upcasting, but that's not what I'm doing). What am I missing? Thanks!

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• Adding Control to Container Control that is in User Control - How to properly initialize?

  - by DougJones

  Let's say I have a user control MyUserControl, which has a container control (it's a server control, but it could just be a Panel) and a dropdownlist. The dropdownlist is not in the container control initially. In it's code-behind, I am overriding OnInit and creating the user control, which includes populating a dropdownlist and adding that dropdownlist to my container control. I have a public property Year, which is an int. Based on the value of Year, I want to populate the dropdownlist. The problem is that in OnInit, year is always 0. On the page Init, I am setting year, but that doesn't run until AFTER the control's Init runs. If I try to set the value on PreInit on the page, the page hasn't initialized the control and I get invalid null reference when setting a value to the control. My question is: How can I properly initialize the control? How can I set the value on the page, before the control actually gets initialized? If I move the control's code to OnLoad, it'll work until I have to do a postback. In this case I need to, though!

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• Design problem with callback functions in android

  - by Franz Xaver

  Hi folks! I'm currently developing an app in android that is accessing wifi values, that is, the application needs to scan for all access point and their specific signal strengths. I know that I have to extend the class BroadcastReceiver overwriting the method BroadcastReceiver.onReceive(Context context, Intent intent) which is called when the values are ready. Perhaps there exist solutions provided by the android system itself but I'm relatively new to android so I could need some help. The problem I encountered is that I got one class (an activity, thus controlled by the user) that needs this scan results for two different things (first to save the values in a database or second, to use them for further calculations but not both at one moment!) So how to design the callback system in order to "transport" the scan results from onReceive(Context context, Intent intent) to the operation intended by the user? My first solution was to define enums for each use case (save or use for calculations) which wlan-interested classes have to submit when querying for the values. But that would force the BroadcastReceiverextending class to save the current enum and use it as a parameter in the callback function of the querying class (this querying class needs to know what it asked for when getting backcalled) But that seems to me kind of dirty ;) So anyone a good idea for this?

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• Qt/C++, Problems with large QImage

  - by David Günzel

  I'm pretty new to C++/Qt and I'm trying to create an application with Visual Studio C++ and Qt (4.8.3). The application displays images using a QGraphicsView, I need to change the images at pixel level. The basic code is (simplified): QImage* img = new QImage(img_width,img_height,QImage::Format_RGB32); while(do_some_stuff) { img->setPixel(x,y,color); } QGraphicsPixmapItem* pm = new QGraphicsPixmapItem(QPixmap::fromImage(*img)); QGraphicsScene* sc = new QGraphicsScene; sc->setSceneRect(0,0,img->width(),img->height()); sc->addItem(pm); ui.graphicsView->setScene(sc); This works well for images up to around 12000x6000 pixel. The weird thing happens beyond this size. When I set img_width=16000 and img_height=8000, for example, the line img = new QImage(...) returns a null image. The image data should be around 512,000,000 bytes, so it shouldn't be too large, even on a 32 bit system. Also, my machine (Win 7 64bit, 8 GB RAM) should be capable of holding the data. I've also tried this version: uchar* imgbuf = (uchar*) malloc(img_width*img_height*4); QImage* img = new QImage(imgbuf,img_width,img_height,QImage::Format_RGB32); At first, this works. The img pointer is valid and calling img-width() for example returns the correct image width (instead of 0, in case the image pointer is null). But as soon as I call img-setPixel(), the pointer becomes null and img-width() returns 0. So what am I doing wrong? Or is there a better way of modifying large images on pixel level? Regards, David

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• Detecting Singularities in a Graph

  - by nasufara

  I am creating a graphing calculator in Java as a project for my programming class. There are two main components to this calculator: the graph itself, which draws the line(s), and the equation evaluator, which takes in an equation as a String and... well, evaluates it. To create the line, I create a Path2D.Double instance, and loop through the points on the line. To do this, I calculate as many points as the graph is wide (e.g. if the graph itself is 500px wide, I calculate 500 points), and then scale it to the window of the graph. Now, this works perfectly for most any line. However, it does not when dealing with singularities. If, when calculating points, the graph encounters a domain error (such as 1/0), the graph closes the shape in the Path2D.Double instance and starts a new line, so that the line looks mathematically correct. Example: However, because of the way it scales, sometimes it is rendered correctly, sometimes it isn't. When it isn't, the actual asymptotic line is shown, because within those 500 points, it skipped over x = 2.0 in the equation 1 / (x-2), and only did x = 1.98 and x = 2.04, which are perfectly valid in that equation. Example: In that case, I increased the window on the left and right one unit each. My question is: Is there a way to deal with singularities using this method of scaling so that the resulting line looks mathematically correct? I myself have thought of implementing a binary search-esque method, where, if it finds that it calculates one point, and then the next point is wildly far away from the last point, it searches in between those points for a domain error. I had trouble figuring out how to make it work in practice, however. Thank you for any help you may give!

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