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• How to differentiate between exceptions i can show the user, and ones i can't?

  - by Ian Boyd

  i have some business logic that traps some logically invalid situations, e.g. trying to reverse a transaction that was already reversed. In this case the correct action is to inform the user: Transaction already reversed or Cannot reverse a reversing transaction or You do not have permission to reverse transactions or This transaction is on a session that has already been closed or This transaction is too old to be reversed The question is, how do i communicate these exceptional cases back to the calling code, so they can show the user? Do i create a separate exception for each case: catch (ETransactionAlreadyReversedException) MessageBox.Show('Transaction already reversed') catch (EReversingAReversingTransactionException) MessageBox.Show('Cannot reverse a reversing transaction') catch (ENoPermissionToReverseTranasctionException) MessageBox.Show('You do not have permission to reverse transactions') catch (ECannotReverseTransactionOnAlredyClosedSessionException) MessageBox.Show('This transaction is on a session that has already been closed') catch (ECannotReverseTooOldTransactionException) MessageBox.Show('This transaction is too old to be reversed') Downside for this is that when there's a new logical case to show the user: Tranasctions created by NSL cannot be reversed i don't simply show the user a message, and instead it leaks out as an unhandled excpetion, when really it should be handled with another MessageBox. The alternative is to create a single exception class: `EReverseTransactionException` With the understanding that any exception of this type is a logical check, that should be handled with a message box: catch (EReverseTransactionException) But it's still understood that any other exceptions, ones that involve, for example, an memory ECC parity error, continue unhandled. In other words, i don't convert all errors that can be thrown by the ReverseTransaction() method into EReverseTransactionException, only ones that are logically invalid cause of the user.

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• How should I handle the case in which a username is already in use?

  - by idealmachine

  I'm a JavaScript programmer and new to PHP and MySQL (want to get into server-side coding). Because I'm trying to learn PHP by building a simple online game (more specifically, correspondence chess), I'm starting by implementing a simple user accounts system. Of course, user registration comes first. What are the best practices for: How I should handle the (likely) possibility that when a user tries to register, the username he has chosen is already in use, particularly when it comes to function return values?($result === true is rather ugly, and I'm not sure whether checking the MySQL error code is the best way to do it either) How to cleanly handle varying page titles?($gPageTitle = '...'; require_once 'bgsheader.php'; is also rather ugly) Anything else I'm doing wrong? In some ways, PHP is rather different from JavaScript... Here is a (rather large) excerpt of the code I have written so far. Note that this is a work in progress and is missing security checks that I will add as my next step. function addUser( $username, $password ) { global $gDB, $gPasswordSalt; $stmt = $gDB->prepare( 'INSERT INTO user(user_name, user_password, user_registration) VALUES(?, ?, NOW())' ); $stmt || trigger_error( 'Failed to prepare statement: ' . htmlspecialchars( $gDB->error ) ); $hashedPassword = hash_hmac( 'sha256', $password, $gPasswordSalt, true ); $stmt->bind_param( 'ss', $username, $hashedPassword ); if( $stmt->execute() ) { return true; } elseif( $stmt->errno == 1062) { return 'exists'; } else { trigger_error( 'Failed to execute statement: ' . htmlspecialchars( $stmt->error ) ); } } $username = $_REQUEST['username']; $password = $_REQUEST['password']; $result = addUser( $username, $password ); if( $result === true ) { $gPageTitle = 'Registration successful'; require_once 'bgsheader.php'; echo '<p>You have successfully registered as ' . htmlspecialchars( $username ) . ' on this site.</p>'; } elseif( $result == 'exists' ) { $gPageTitle = 'Username already taken'; require_once 'bgsheader.php'; echo '<p>Someone is already using the username you have chosen. Please try using another one instead.'; } else { trigger_error('This should never happen'); } require_once 'bgsfooter.php';

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• Is it possible to call the main(String[] args) after catching an exception?

  - by Jason

  I'm working on a Serpinski triangle program that asks the user for the levels of triangles to draw. In the interests of idiot-proofing my program, I put this in: Scanner input= new Scanner(System.in); System.out.println(msg); try { level= input.nextInt(); } catch (Exception e) { System.out.print(warning); //restart main method } Is it possible, if the user punches in a letter or symbol, to restart the main method after the exception has been caught?

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• WP7 - Cancelling ContextMenu click event propagation

  - by Praetorian

  I'm having a problem when the Silverlight toolkit's ContextMenu is clicked while it is over a UIElement that has registered a Tap event GestureListener. The context menu click propagates to the underlying element and fires its tap event. For instance, say I have a ListBox and each ListBoxItem within it has registered both a ContextMenu and a Tap GestureListener. Assume that clicking context menu item2 is supposed to take you to Page1.xaml, while tapping on any of ListBox items themselves is supposed to take you to Page2.xaml. If I open the context menu on item1 in the ListBox, then context menu item2 is on top of ListBox item2. When I click on context menu item2 I get weird behavior where the app navigates to Page1.xaml and then immediately to Page2.xaml because the click event also triggered the Tap gesture for ListBox item2. I've verified in the debugger that it is always the context menu that receives the click event first. How do I cancel the context menu item click's routed event propagation so it doesn't reach ListBox item2? Thanks for your help!

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• Common Utility for Exception Searching

  - by Andrew

  I wrote this little helper method to search the exception chain for a particular exception (either equals or super class). However, this seems like a solution to a common problem, so was thinking it must already exist somewhere, possibly in a library I have already imported. So, any ideas on if/where this might exist? boolean exceptionSearch(Exception base, Class<?> search) { Throwable e = base; do { if (search.isAssignableFrom(e.getClass())) { return true; } } while ((e = e.getCause()) != null); return false; }

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• How to get the name of the method that caused the exception

  - by SKumar

  My code looks as below. try { _productRepo.GetAllProductCategories(); } catch (Exception ex) { //Do Something } I need a way to show the method name, suppose in the above case if any exception is thrown in the GetAllProductCategories() method, I need to get this method name i.e. "GetAllProductCategories()" as my result. Can any one suggest me how to do this?

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• Confirmation before closing

  - by saeed

  Hi I am using c# .net windows form application. I have a combo box and a text box and a close window button. Now If I make any change in the combo box or textbox and click on the close window button, it should prompt the user to save the modifications.. If no modification are made ( The user will just run the application, doesnt make any modification) then it should not prompt the user. It should close directly.. How can I do this?

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• Handling Denormalized Schema with Eclipselink

  - by iamrohitbanga

  Hello All I have a denormalized table containing employee information. The fields are employee id, name and department name. The primary key is a composite one consisting of all three fields. An employee can belong to multiple departments. I want to read/write the objects in the table using the Eclipselink Dynamic Persistence API (which is infact a wrapper on top of JPA descriptors etc.). Example Data: 1 e1 dep1 2 e1 dep2 3 e2 dep1 4 e2 dep3 5 e3 dep1 5 e3 dep2 5 e3 dep3 A normal ReadAllQuery (select query) on the table returns a DynamicEntity corresponding to each row in the table. However I want to club all entities based on the emp id and return all the departments he belongs to as a list. I can merge the entities after retrieving them but if I can use some Eclipselink feature out of the box then it would be better. One way to do the read is the following: I create two dynamic types corresponding to employee: Having id,name as the primary key Having id, department as the primary key, I create a OneToManyMapping from the first type to the second one. Then when I query the first type it does return the departments to which employee belongs as a list of DynamicEntity of the second type. This satisfies the read scenario. Is there a better way of doing this? Is this inherently supported by Eclipselink or JPA? I cannot get the same dynamic type configuration working for the write scenario. This is because when I write the changes using the writeObject method of UnitOfWork, it generates insert queries which enter the following entries in the table id name department 102 emp_102 102 st 102 dep_102 102 dep_102 102 dep_102 instead of: id name department 102 emp_102 st 102 emp_102 dep_102 102 emp_102 dep_102 102 emp_102 dep_102 Is there any way I can get write to work with this schema using eclipselink? I want to avoid doing the heavy lifting of merging the rows for such a denormalized schema or generating each row before doing a write. Is there no clean way of doing this using Eclipselink or JPA? Thanks in Advance.

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• In Asp.net i'm not able to catch any exception properly?

  - by Anand

  In Asp.net (c#),i'm not able to catch exception(FileNotFoundException) properly... i don't know the reason..Actually File s not there..But catch statement fails to catch the exception.. here is the code.. try { System.Drawing.Image imgg1 = System.Drawing.Image.FromFile(Server.MapPath("").ToString() + "\\images\\img1.jpg"); } catch (FileNotFoundException) { Response.Write("<script>alert('Please Select and upload Student's Photo');</script>"); }

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• Distinguishing between failure and end of file in read loop

  - by celtschk

  The idiomatic loop to read from an istream is while (thestream >> value) { // do something with value } Now this loop has one problem: It will not distinguish if the loop terminated due to end of file, or due to an error. For example, take the following test program: #include <iostream> #include <sstream> void readbools(std::istream& is) { bool b; while (is >> b) { std::cout << (b ? "T" : "F"); } std::cout << " - " << is.good() << is.eof() << is.fail() << is.bad() << "\n"; } void testread(std::string s) { std::istringstream is(s); is >> std::boolalpha; readbools(is); } int main() { testread("true false"); testread("true false tr"); } The first call to testread contains two valid bools, and therefore is not an error. The second call ends with a third, incomplete bool, and therefore is an error. Nevertheless, the behaviour of both is the same. In the first case, reading the boolean value fails because there is none, while in the second case it fails because it is incomplete, and in both cases EOF is hit. Indeed, the program above outputs twice the same line: TF - 0110 TF - 0110 To solve this problem, I thought of the following solution: while (thestream >> std::ws && !thestream.eof() && thestream >> value) { // do something with value } The idea is to detect regular EOF before actually trying to extract the value. Because there might be whitespace at the end of the file (which would not be an error, but cause read of the last item to not hit EOF), I first discard any whitespace (which cannot fail) and then test for EOF. Only if I'm not at the end of file, I try to read the value. For my example program, it indeed seems to work, and I get TF - 0100 TF - 0110 So in the first case (correct input), fail() returns false. Now my question: Is this solution guaranteed to work, or was I just (un-)lucky that it happened to give the desired result? Also: Is there a simpler (or, if my solution is wrong, a correct) way to get the desired result?

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• Exporting to CSV with dynamic field type handling

  - by serhio

  I have to do an export from DB to CSV. field; fileld; field... etc Have 3 types of fields: Alpha, Numeric and Bool respresented as "alphaValue",intValue and True/False. I try to encapsulate this in a fields collection, in order to export if alpha then set "", if Bool=True/False if numeric let as is. and try to build a CsvField class: Public Structure?Class CsvField(Of T As ???) End Structure Enum FieldType Alpha Bool Numeric End Enum any suggestions welcomed.

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• C# wpf: Need to add mouseclick event to certain text within a textbox

  - by Michael

  I have a textbox with a paragraph of information. There are certain words in the paragraph that i want the user to be able to click on, and when clicked, a different textbox is populated with more information. I know that you can have the event for the whole textbox, but that isn't want i want. I only want to call that event when certain words within the box are clicked.

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• C# Dynamic Keyword exception handling

  - by user972255

  The below code throws an exception when executing this line (i.e. something.Add(name)). I want to catch the actual exception when executing this. I mean I don't want to use catch(Exception ex) instead of that I want to know what is the correct exception thrown here. try { dynamic name= "test"; var something = new List<decimal>(); something.Add(name); } catch(Exception ex) { throw ex; } Thanks in advance.

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• WPF Event Handler in Another Class

  - by Nathan Tornquist

  I have built a series of event handlers for some custom WPF controls. The event handles format the text displayed when the user enters or leaves a textbox based on the type of data contained (Phone number, zip code, monetary value, etc.) Right now I have all of the events locally in the C# code directly attached to the xaml. Because I have developed a could controls, this means that the logic is repeated a lot, and if I want to change the program-wide functionality I would have to make changes everywhere the event code is located. I am sure there is a way to put all of my event handlers in a single class. Can anyone help point me in the correct direction? I saw this article: Event Handler located in different class than MainWindow But I'm not sure if it directly relates to what I'm doing. I would rather make small changes to the existing logic that I have, as it works, then rewrite everything into commands. I would essentially like to something like this if possible: LostFocus="ExpandedTextBoxEvents.TextBox_LostFocus" It is easy enough to do something like this: private void TextBoxCurrencyGotFocus(object sender, RoutedEventArgs e) { ExpandedTextBoxEvents.TextBoxCurrencyGotFocus(sender, e); } private void TextBoxCurrencyLostFocus(object sender, RoutedEventArgs e) { ExpandedTextBoxEvents.TextBoxCurrencyLostFocus(sender, e); } But that is less elegant.

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• How do I propagate an exception thrown by croak in forked child to parent/foreground process?

  - by Pedro Silva

  Throwing an exception via croak in a forked child process seems to print the error as a background process would. That is, it clobbers the shell prompt. If I die instead of croak, the the error message pops up as a foreground process. I've trying to find out why that is in the Carp documentation without any luck. Here's what I mean. The croak version: $ perl Wrapper.pm $ error: ... does not exist at Wrapper.pm line 624 The die version: $ perl Wrapper.pm error: ... does not exist at Wrapper.pm line 515. I tried trapping the fork and printing $@ to STDERR and exiting, but that didn't have an effect. Any ideas? I'd like to be able to use croak in this particular case.

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• How to solve Only Web services with a [ScriptService] attribute on the class definition can be called from script

  - by NevenHuynh

  I attempt to use webservice return POCO class generated from entity data model as JSON when using Jquery AJAX call method in webservice. but I have problem with error "Only Web services with a [ScriptService] attribute on the class definition can be called from script", and getting stuck in it, Here is my code : namespace CarCareCenter.Web.Admin.Services { /// <summary> /// Summary description for About /// </summary> [WebService(Namespace = "http://tempuri.org/")] [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)] [System.ComponentModel.ToolboxItem(false)] // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. // [System.Web.Script.Services.ScriptService] public class About : System.Web.Services.WebService { [ScriptMethod(ResponseFormat = ResponseFormat.Json)] [WebMethod] public static Entities.Category getAbout() { Entities.Category about = new Entities.Category(); using (var context = new CarCareCenterDataEntities()) { about = (from c in context.Categories where c.Type == "About" select c).SingleOrDefault(); } return about; } } } aspx page : <script type="text/javascript"> $(document).ready(function () { $.ajax({ type: 'POST', dataType: 'json', contentType: 'application/json; charset=utf-8', url: '/Services/About.asmx/getAbout', data: '{}', success: function (response) { var aboutContent = response.d; alert(aboutContent); $('#title-en').val(aboutContent.Name); $('#title-vn').val(aboutContent.NameVn); $('#content-en').val(aboutContent.Description); $('#content-vn').val(aboutContent.DescriptionVn); $('#id').val(aboutContent.CategoryId); }, failure: function (message) { alert(message); }, error: function (result) { alert(result); } }); $('#SaveChange').bind('click', function () { updateAbout(); return false; }); $('#Reset').bind('click', function () { getAbout(); return false; }) }); function updateAbout() { var abt = { "CategoryId": $('#id').val(), "Name": $('#title-en').val(), "NameVn": $('#title-vn').val(), "Description": $('#content-en').val(), "DescriptionVn": $('#content-vn').val() }; $.ajax({ type: "POST", url: "AboutManagement.aspx/updateAbout", data: JSON.stringify(abt), contentType: "application/json; charset=utf-8", dataType: "json", success: function (response) { var aboutContent = response.d; $('#title-en').val(aboutContent.Name); $('#title-vn').val(aboutContent.NameVn); $('#content-en').val(aboutContent.Description); $('#content-vn').val(aboutContent.DescriptionVn); }, failure: function (message) { alert(message); }, error: function (result) { alert(result); } }); } </script> Do any approaches to solve it ? Please help me . Thanks

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• GetWindowLongPtr fails if called when handling WM_CREATE

  - by Semen Semenych

  Calling the GetWindowLongPtr function for a dialog box with the DWL_USER parameter fails when done from the WM_CREATE handler. It gives no error (checked that, the return value is always zero), which, according to the MSDN documentation, occurs only if SetWindowLongPtr has not been called previously. However, I call it after registering the window class, and properly call the SetWindowPos after that. Finally, calling GetWindowLongPtr in any other event handler, that is, later than WM_CREATE, works fine. Is there something I'm missing in the initialization sequence, or maybe the messages are sent in some not so obvious order?

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• Mapping the System.Exception with FaultException

  - by user357342

  I have used exception sheilding feature of application block, to map System.Exception with class that is marked as DataContract. It works very well. But When I have mapped the System.Exception with FaultException, I got the below error message. "An error has occurred while consuming this service. Please contact your administrator for more information. Error ID: fe2d28b5-8d26-430e-baf4-fe4b39da853c" Please let me know whether I can map the System.Exception with FaultException

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• Window resolution handling without javascript

  - by Sai Sasdhar

  Is there any CSS property to deal window resolution. I created a HTML page taking total resolution width as 1424px.When I open it on different resolution I see a scroll bar & resolution of HTML does not adjust automatically. I don't want the scrollbar to be seen in maximized size of the page. Is it possible without using javascript.At the same time how to increase the resolution when itself is created in lower res.

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• Php string handling triks

  - by Dam

  Hi my question Need to get the 10 word before and 10 words after for the given text . i mean need to start the 10 words before the keyword and end with 10 word after the key word. Given text : "Twenty-three" The main trick : content having some html tags etc .. tags need to keep that tag with this content only . need to display the words from 10before - 10after content is bellow : <div id="hpFeatureBoxInt"><h3><a href="/go/homepage/i/int/news/world/1/-/news/1/hi/world/europe/8592190.stm">Suicide bombings hit Moscow Metro</a></h3><p>Past suicide bombings in Moscow have been blamed on Islamist rebels At least 35 people have been killed after two female suicide bombers blew themselves up on Moscow Metro trains in the morning rush hour,<h2><span class="dy">Top News Story</span></h2> officials say.<img height="150" width="201" alt="Emergency services carry a body from a Metro station in Moscow (29 March 2010)" src="http://wwwimg.bbc.co.uk/feedengine/homepage/images/_47550689_moscowap203_201x150.jpg">Twenty-three died in the first blast at 0756 (0356 GMT) as a<a href="#"> train stood </a>at the central Lubyanka station, beneath the offices of the FSB intelligence agency.About 40 minutes later, a second explosion ripped through a train at Park Kultury, leaving another 12 dead.No-one has said they carried out the worst attack in the capital since 2004. </p><p id="fbilisten"><a href="/go/homepage/i/int/news/heading/-/news/">More from BBC News</a></p></div> Thank you

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• Handling static files with Django / lighttpd

  - by ptikobj

  I know that there is already a question (actually some more) about this, but the answers to them didn't help me out very much, as I am pretty new to lighttpd. I have one folder which contains .pdf-files. When doing a HttpResponseRedirect to the locations of one of those .pdf-files, the user should be able to download the .pdf file (or view it in the browser). Right now, Django just redirects to my "home" html page, without showing any pdf-file. Somehow, I will have to tell lighttpd that Django shouldn't handle this directory anymore. Is this the only thing I need to do? If yes, how should i do it?

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• Handling very large lists of objects without paging?

  - by user246114

  Hi, I have a class which can contain many small elements in a list. Looks like: public class Farm { private ArrayList<Horse> mHorses; } just wondering what will happen if the mHorses array grew to something crazy like 15,000 elements. I'm assuming that trying to write and read this from the datastore would be crazy, because I'd get killed on the serialization process. It's important that I can get the entire array in one shot without paging, and each Horse element may only have two string properties in it, so they are pretty lightweight: public class Horse { private String mId; private String mName; } I don't need these horses indexed at all. Does it sound reasonable to just store the mHorse array as a raw Text field, and force my clients to do the deserialization? Something like: public class Farm { private Text mHorsesSerialized; } then whenever the client receives a Farm instance, it has to take the raw string of horses, and split it in order to reinstantiate the list, something like: // GWT client perhaps Farm farm = rpcCall.getMyFarm(); String horsesSerialized = farm.getHorses(); String[] horseBlocks = horsesSerialized.split(","); for (int i = 0; i < horseBlocks.length; i++) { // .. continue deserializing the individual objects ... } yeah... so hopefully it would be quick to read a Farm instance from the datastore, and the serialization penalty is paid by the client, Thanks

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• error handling with .post()

  - by meo

  I have to modify a project written by someone else. Because the code is a mess i can't really change this $.post() (or replace it by $.ajax()). What i need to do, is to know if the post returns something else then json and return it. $.post('balbal.html', json, function(data) { ... my coude ... }, 'json') I can see the post response i the console.log. Is there a simple way to retrieve it?

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• Handling large (object) datasets with PHP

  - by Aron Rotteveel

  I am currently working on a project that extensively relies on the EAV model. Both entities as their attributes are individually represented by a model, sometimes extending other models (or at least, base models). This has worked quite well so far since most areas of the application only rely on filtered sets of entities, and not the entire dataset. Now, however, I need to parse the entire dataset (IE: all entities and all their attributes) in order to provide a sorting/filtering algorithm based on the attributes. The application currently consists of aproximately 2200 entities, each with aproximately 100 attributes. Every entity is represented by a single model (for example Client_Model_Entity) and has a protected property called $_attributes, which is an array of Attribute objects. Each entity object is about 500KB, which results in an incredible load on the server. With 2000 entities, this means a single task would take 1GB of RAM (and a lot of CPU time) in order to work, which is unacceptable. Are there any patterns or common approaches to iterating over such large datasets? Paging is not really an option, since everything has to be taken into account in order to provide the sorting algorithm.

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• Global Exception Handlers in Java

  - by Samuh

  I am thinking of setting up a global, default Exception handler for my (Android) Mobile application(which uses Java syntax) using Thread.setDefaultUncaughtExceptionHandler(...) call. I am thinking of just displaying an Alert Dialog with appropriate message to the user. Are there any gotchas, caveats and rules that one needs to follow when setting DefaultExceptionHandlers? Any best practices like making sure that the process is killed, full stack trace is written to logs etc. ? Links to documentation, tutorials etc. that can throw some light on this are welcome. Thanks.

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