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  • garbage collector Issue

    - by Eslam
    this question is like my previous one Given: 3. interface Animal { void makeNoise(); } 4. class Horse implements Animal { 5. Long weight = 1200L; 6. public void makeNoise() { System.out.println("whinny"); } 7. } 8. public class Icelandic extends Horse { 9. public void makeNoise() { System.out.println("vinny"); } 10. public static void main(String[] args) { 11. Icelandic i1 = new Icelandic(); 12. Icelandic i2 = new Icelandic(); 13. Icelandic i3 = new Icelandic(); 14. i3 = i1; i1 = i2; i2 = null; i3 = i1; 15. } 16. } When line 14 is reached, how many objects are eligible for the garbage collector? A. 0 B. 1 C. 2 D. 3 E. 4 F. 6 i choosed A but the right answer is E, but i don't know Why?

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  • Android NDK import-module / code reuse

    - by Graeme
    Morning! I've created a small NDK project which allows dynamic serialisation of objects between Java and C++ through JNI. The logic works like this: Bean - JavaCInterface.Java - JavaCInterface.cpp - JavaCInterface.java - Bean The problem is I want to use this functionality in other projects. I separated out the test code from the project and created a "Tester" project. The tester project sends a Java object through to C++ which then echo's it back to the Java layer. I thought linking would be pretty simple - ("Simple" in terms of NDK/JNI is usually a day of frustration) I added the JNIBridge project as a source project and including the following lines to Android.mk: NDK_MODULE_PATH=.../JNIBridge/jni/" JNIBridge/jni/JavaCInterface/Android.mk: ... include $(BUILD_STATIC_LIBRARY) JNITester/jni/Android.mk: ... include $(BUILD_SHARED_LIBRARY) $(call import-module, JavaCInterface) This all works fine. The C++ files which rely on headers from JavaCInterface module work fine. Also the Java classes can happily use interfaces from JNIBridge project. All the linking is happy. Unfortunately JavaCInterface.java which contains the native method calls cannot see the JNI method located in the static library. (Logically they are in the same project but both are imported into the project where you wish to use them through the above mechanism). My current solutions are are follows. I'm hoping someone can suggest something that will preserve the modular nature of what I'm trying to achieve: My current solution would be to include the JavaCInterface cpp files in the calling project like so: LOCAL_SRC_FILES := FunctionTable.cpp $(PATH_TO_SHARED_PROJECT)/JavaCInterface.cpp But I'd rather not do this as it would lead to me needing to update each depending project if I changed the JavaCInterface architecture. I could create a new set of JNI method signatures in each local project which then link to the imported modules. Again, this binds the implementations too tightly.

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  • little java help....

    - by jona
    Hi I am doing some practice problems and trying to print a diagonal line like the example below. I have writen the program you see below and I honestly dont understand what I am doing wrong. I m a java beginner and I cant see how to find the error. Example ( If you only see a straight line of stars...then imagine it diagonally....from top left to bottom right) * * * * * code: class Diagonal{ public static void main(String args[]) { int row, col; for(row = 1; row < 6; row++) { for(col = 1; col <= row; col++) { if(col==row){ System.out.print("*"); } else{ System.out.print(""); } System.out.println(); } } } } I am trying to learn for loops because they really confuse me. Another practice is to print a similar diagonal line but this time from right to left. I cant do that without getting this right however :( I believe they will be pretty similar? Above my reasining is this: As long as the column # is the same as the row number the print the line or otherwise leave a blank....what's wrong with how i did it? THANK YOU!

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  • How to create a list/structure? in JAVA

    - by lox
    i have to create a list of ,let's say 50 people, (in JAVA) and display the list, and i don't really know how to do that. so this is what i have tried to do so far . please correct and complete some of my code . public class Person { String name; String stuff; } public class CreatePerson { public static void ang() { ArrayList<Person> thing=new ArrayList<Person>(); Scanner diskScanner = new Scanner(in); for(int i=0; i<50; i++){ Person pers = new Person(); out.print("name: "); pers.name=diskScanner.nextLine(); out.print("stuff: "); pers.stuff=diskScanner.nextLine(); thing.add(pers); break; } // Display people for (int i=0; i<50; i++) { out.println(??);{ } } }}

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  • IIS6, ASP.NET MVC 1 and random slowdowns

    - by Mr Snuffle
    I've recently deployed a MVC application to an IIS6 web server. One strange behaviour I've been having is the load times will randomly blow up to 30sec+ and then return to normal. Our tests have shown this occurring on multiple connections at the same time. Once the wait has passed, the site become responsive again. It's completely random when this will occur, but will probably happen about once every 15 minutes or so. My first thought was the application was being restarted by the web server for some reason, but I determined this wasn't the case because the process recycling is set very infrequently, and I placed some logging in the application startup. It's also nothing to do with the database connection. This slowdown happens simply by moving between static pages too. I've watched the database with a SQL profiler, and nothing is hitting it when these slowdowns occur. Finally, I've placed entry and exit logging on my controller actions, the slowdown always happens outside of the controller. The entry and exit time for a controller action is always appropriately fast. Does anyone have any ideas of what could be causing this? I've tried running it locally on IIS7 and I haven't had the issue. I can only think it's something to do with our hosting provider.

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  • How to: generate UnhandledException?

    - by serhio
    I use this code to catch the WinForm application UnhandledException. [STAThread] static void Main(string[] args) { // Add the event handler for handling UI thread exceptions to the event. Application.ThreadException += new System.Threading.ThreadExceptionEventHandler(Application_ThreadException); // Set the unhandled exception mode to force all Windows Forms errors // to go through our handler. Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException); // Add the event handler for handling non-UI thread exceptions to the event. AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException); try { Application.Run(new MainForm()); } catch.... There I will try to restart the application. Now my problem is to simulate a exception like this. I tried before try (in main): throw new NullReferenceException("test"); VS caught it. Tried also in MainForm code with button : private void button1_Click(object sender, EventArgs ev) { ThreadPool.QueueUserWorkItem(new WaitCallback(TestMe), null); } protected void TestMe(object state) { string s = state.ToString(); } did not help, VS caught it, even in Release mode. How should I, finally, force the application generate UnhandleldException? Will I be able to restart the application in CurrentDomain_UnhandledException?

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  • Trying to create a .NET DLL to be used with Non-.NET Application

    - by Changeling
    I am trying to create a .NET DLL so I can use the cryptographic functions with my non .NET application. I have created a class library so far with this code: namespace AESEncryption { public class EncryptDecrypt { private static readonly byte[] optionalEntropy = { 0x21, 0x05, 0x07, 0x08, 0x27, 0x02, 0x23, 0x36, 0x45, 0x50 }; public interface IEncrypt { string Encrypt(string data, string filePath); }; public class EncryptDecryptInt:IEncrypt { public string Encrypt(string data, string filePath) { byte[] plainKey; try { // Read in the secret key from our cipher key store byte[] cipher = File.ReadAllBytes(filePath); plainKey = ProtectedData.Unprotect(cipher, optionalEntropy, DataProtectionScope.CurrentUser); // Convert our plaintext data into a byte array byte[] plainTextBytes = Encoding.ASCII.GetBytes(data); MemoryStream ms = new MemoryStream(); Rijndael alg = Rijndael.Create(); alg.Mode = CipherMode.CBC; alg.Key = plainKey; alg.IV = optionalEntropy; CryptoStream cs = new CryptoStream(ms, alg.CreateEncryptor(), CryptoStreamMode.Write); cs.Write(plainTextBytes, 0, plainTextBytes.Length); cs.Close(); byte[] encryptedData = ms.ToArray(); return Convert.ToString(encryptedData); } catch (Exception ex) { return ex.Message; } } } } } In my VC++ application, I am using the #import directive to import the TLB file created from the DLL, but the only available functions are _AESEncryption and LIB_AES etc I don't see the interface or the function Encrypt. When I try to instantiate so I can call the functions in my VC++ program, I use this code and get the following error: HRESULT hr = CoInitialize(NULL); IEncryptPtr pIEncrypt(__uuidof(EncryptDecryptInt)); error C2065: 'IEncryptPtr': undeclared identifier error C2146: syntax error : missing ';' before identifier 'pIEncrypt'

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  • Hide a single content block from search engines?

    - by jonas
    A header is automatically added on top of each content URL, but its not relevant for search and messing up the all the results beeing the first line of every page (in the code its the last line but visually its the first, which google is able to notice) Solution1: You could put the header (content to exculde from google searches) in an iframe with a static url domain.com/header.html and a <meta name="robots" content="noindex" /> ? - are there takeoffs of this solution? Solution2: You could deliver it conditionally by apache mod rewrite, php or javascript -takeoff(?): google does not like it? will google ever try pages with a standard users's useragent and compare? -takeoff: The hidden content will be missing in the google cache version as well... example: add-header.php: <?php $path = $_GET['path']; echo file_get_contents($_SERVER["DOCUMENT_ROOT"].$path); ?> apache virtual host config: RewriteCond %{HTTP_USER_AGENT} !.*spider.* [NC] RewriteCond %{HTTP_USER_AGENT} !Yahoo.* [NC] RewriteCond %{HTTP_USER_AGENT} !Bing.* [NC] RewriteCond %{HTTP_USER_AGENT} !Yandex.* [NC] RewriteCond %{HTTP_USER_AGENT} !Baidu.* [NC] RewriteCond %{HTTP_USER_AGENT} !.*bot.* [NC] RewriteCond %{SCRIPT_FILENAME} \.htm$ [NC,OR] RewriteCond %{SCRIPT_FILENAME} \.html$ [NC,OR] RewriteCond %{SCRIPT_FILENAME} \.php$ [NC] RewriteRule ^(.*)$ /var/www/add-header.php?path=%1 [L]

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  • Hibernate: Walk millions of rows and don't leak memory

    - by Autocracy
    The below code functions, but Hibernate never lets go of its grip of any object. Calling session.clear() causes exceptions regarding fetching a joined class, and calling session.evict(currentObject) before retrieving the next object also fails to free the memory. Eventually I exhaust my heap space. Checking my heap dumps, StatefulPersistenceContext is the garbage collector's root for all references pointing to my objects. public class CriteriaReportSource implements JRDataSource { private ScrollableResults sr; private Object currentObject; private Criteria c; private static final int scrollSize = 10; private int offset = 1; public CriteriaReportSource(Criteria c) { this.c = c; advanceScroll(); } private void advanceScroll() { // ((Session) Main.em.getDelegate()).clear(); this.sr = c.setFirstResult(offset) .setMaxResults(scrollSize) .scroll(ScrollMode.FORWARD_ONLY); offset += scrollSize; } public boolean next() { if (sr.next()) { currentObject = sr.get(0); if (sr.isLast()) { advanceScroll(); } return true; } return false; } public Object getFieldValue(JRField jrf) throws JRException { Object retVal = null; if(currentObject == null) { return null; } try { retVal = PropertyUtils.getProperty(currentObject, jrf.getName()); } catch (Exception ex) { Logger.getLogger(CriteriaReportSource.class.getName()).log(Level.SEVERE, null, ex); } return retVal; } }

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  • Using mod-rewrite to conditionally select existing file in a subdirectory based on Host header?

    - by Kevin Hakanson
    I'm working through a problem where I want to select a different static content file based on the incoming Host header. The simple example is a mapping from URLs to files like this: www.example.com/images/logo.gif - \images\logo.gif skin2.example.com/images/logo.gif - \images\skin2\logo.gif skin3.example.com/images/logo.gif - \images\skin3logo.gif I have this working with the following RewriteRules, but I don't like how I have to repeat myself so much. Each host has the same set of rules, and each RewriteCond and RewriteRule has the same path. I'd like to use the RewriteMap, but I don't know how to use it to map the %{HTTP_HOST} to the path. <VirtualHost *:80> DocumentRoot "C:/Program Files/Apache Software Foundation/Apache2.2/htdocs" ServerName www.example.com ServerAlias skin2.example.com ServerAlias skin3.example.com RewriteEngine On RewriteCond %{HTTP_HOST} skin2.example.com RewriteCond %{DOCUMENT_ROOT}$1/skin2/$2 -f RewriteRule ^(.*)/(.*) $1/skin2/$2 [L] RewriteCond %{HTTP_HOST} skin3.example.com RewriteCond %{DOCUMENT_ROOT}$1/skin3/$2 -f RewriteRule ^(.*)/(.*) $1/skin3/$2 [L] </VirtualHost> The concept behind the rules is if the same filename exists in a subdirectory for that host, use it instead of the direct targeted file. This uses host based subdirectories at the lowest level, and not a top level subdirectory to separate content.

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  • Get an array of structures from native dll to c# application

    - by PaulH
    I have a C# .NET 2.0 CF project where I need to invoke a method in a native C++ DLL. This native method returns an array of type TableEntry. At the time the native method is called, I do not know how large the array will be. How can I get the table from the native DLL to the C# project? Below is effectively what I have now. // in C# .NET 2.0 CF project [StructLayout(LayoutKind.Sequential)] public struct TableEntry { [MarshalAs(UnmanagedType.LPWStr)] public string description; public int item; public int another_item; public IntPtr some_data; } [DllImport("MyDll.dll", CallingConvention = CallingConvention.Winapi, CharSet = CharSet.Auto)] public static extern bool GetTable(ref TableEntry[] table); SomeFunction() { TableEntry[] table = null; bool success = GetTable( ref table ); // at this point, the table is empty } // In Native C++ DLL std::vector< TABLE_ENTRY > global_dll_table; extern "C" __declspec(dllexport) bool GetTable( TABLE_ENTRY* table ) { table = &global_dll_table.front(); return true; } Thanks, PaulH

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  • How to store session values with Node.js and mongodb?

    - by Tirithen
    How do I get sessions working with Node.js, [email protected] and mongodb? I'm now trying to use connect-mongo like this: var config = require('../config'), express = require('express'), MongoStore = require('connect-mongo'), server = express.createServer(); server.configure(function() { server.use(express.logger()); server.use(express.methodOverride()); server.use(express.static(config.staticPath)); server.use(express.bodyParser()); server.use(express.cookieParser()); server.use(express.session({ store: new MongoStore({ db: config.db }), secret: config.salt })); }); server.configure('development', function() { server.use(express.errorHandler({ dumpExceptions: true, showStack: true })); }); server.configure('production', function() { server.use(express.errorHandler()); }); server.set('views', __dirname + '/../views'); server.set('view engine', 'jade'); server.listen(config.port); I'm then, in a server.get callback trying to use req.session.test = 'hello'; to store that value in the session, but it's not stored between the requests. It probobly takes something more that this to store session values, how? Is there a better documented module than connect-mongo?

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  • C++ destructors causing crash's

    - by larsonator
    ok, so i got a some what intricate program that simulates the uni systems of students, units, and students enrolling in units. Students are stored in a binary search tree, Units are stored in a standard list. Student has a list of Unit Pointers, to store which units he/she is enrolled in Unit has a list of Student pointers, to store students which are enrolled in that unit. The unit collections (storing units in a list) as made as a static variable where the main function is, as is the Binary search tree of students. when its finaly time to close the program, i call the destructors of each. but at some stage, during the destructors on the unit side, Unhandled exception at 0x002e4200 in ClassAllocation.exe: 0xC0000005: Access violation reading location 0x00000000. UnitCollection destructor: UnitCol::~UnitCol() { list<Unit>::iterator itr; for(itr = UnitCollection.begin(); itr != UnitCollection.end();) { UnitCollection.pop_front(); itr = UnitCollection.begin(); } } Unit Destructor Unit::~Unit() { } now i got the same sorta problem on the student side of things BST destructors void StudentCol::Destructor(const BTreeNode * r) { if(r!= 0) { Destructor(r->getLChild()); Destructor(r->getRChild()); delete r; } } StudentCol::~StudentCol() { Destructor(root); } Student Destructor Student::~Student() { } so yeah any help would be greatly appreciated

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  • Using jquery Autocomplete on textbox control in c#

    - by Abid Ali
    When I run this code I get alert saying Error. My Code: <script type="text/javascript"> debugger; $(document).ready(function () { SearchText(); }); function SearchText() { $(".auto").autocomplete({ source: function (request, response) { $.ajax({ type: "POST", contentType: "application/json; charset=utf-8", url: "Default.aspx/GetAutoCompleteData", data: "{'fname':'" + document.getElementById('txtCategory').value + "'}", dataType: "json", success: function (data) { response(data.d); }, error: function (result) { alert("Error"); } }); } }); } </script> [WebMethod] public static List<string> GetAutoCompleteData(string CategoryName) { List<string> result = new List<string>(); using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["DbConnection"].ConnectionString)) { using (SqlCommand cmd = new SqlCommand("select fname from tblreg where fname LIKE '%'+@CategoryText+'%'", con)) { con.Open(); cmd.Parameters.AddWithValue("@CategoryText", CategoryName); SqlDataReader dr = cmd.ExecuteReader(); while (dr.Read()) { result.Add(dr["fname"].ToString()); } return result; } } } I want to debug my function GetAutoCompleteData but breakpoint is not fired at all. What's wrong in this code? Please guide. I have attached screen shot above.

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  • Table view with custom cell (programmatically)

    - by gotye
    Hey guys, So far, I used to create custom nibs to make my cell as I wanted but this time, the height of a cell will change from one to another so that I can't create a fixed-size cell's nib. So I decided to create it programmatically ... Is the way below the good way to achieve it ? // Customize the appearance of table view cells. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; UILabel *pseudoAndDate = [[UILabel alloc] initWithFrame:CGRectMake(0.0,0.0,320.0,20.0)]; [pseudoAndDate setTag:1]; [cell addSubview:pseudoAndDate]; [pseudoAndDate release]; } CommentRecord *thisRecord = [comments objectAtIndex:[indexPath row]]; UILabel *label = (UILabel *)[cell viewWithTag:1]; [label setText:[NSString stringWithFormat:@"%@ | %@",thisRecord.author,thisRecord.date]]; return cell; } or .. am i missing something here ? Cause so far it doesn't seem to work ;) Thanks, Gotye.

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  • Different users get the same cookie - value in .ASPXANONYMOUS

    - by Malcolm Frexner
    My site allows anonymous users. I saw that under heavy load user get sometimes profile values from other users. This happens for anonymous users. I logged the access to profile data: /// <summary> /// /// </summary> /// <param name="controller"></param> /// <returns></returns> public static string ProfileID(this Controller controller ) { if (ApplicationConfiguration.LogProfileAccess) { StringBuilder sb = new StringBuilder(); (from header in controller.Request.Headers.ToPairs() select string.Concat(header.Key, ":", header.Value, ";")).ToList().ForEach(x => sb.Append(x)); string log = string.Format("ip:{0} url:{1} IsAuthenticated:{2} Name:{3} AnonId:{4} header:{5}", controller.Request.UserHostAddress, controller.Request.Url.ToString(), controller.Request.IsAuthenticated, controller.User.Identity.Name, controller.Request.AnonymousID, sb); _log.Debug(log); } return controller.Request.IsAuthenticated ? controller.User.Identity.Name : controller.Request.AnonymousID; } I can see in the log that user realy get the same cookievalue for .ASPXANONYMOUS even if they have different IP. Just to be safe I removed dependency injection for the FormsAuthentication. I dont use OutputCaching. My web.config has this setting for authentication: <anonymousIdentification enabled="true" cookieless="UseCookies" cookieName=".ASPXANONYMOUS" cookieTimeout="30" cookiePath="/" cookieRequireSSL="false" cookieSlidingExpiration="true" /> <authentication mode="Forms"> <forms loginUrl="~/de/Account/Login" /> </authentication> Does anybody have an idea what else I could log or what I should have a look at?

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  • How to redirect page

    - by sharun
    Hi i created one java application in which i tried to open my company's standard login page and i planned to redirect the link to open my own design page. Standard login page is displayed, instead of going to my own design page as usual its going to mail page. After sign out the mail page i'm gettting my own design page. But my need is, when i sign in the standard login page it should diplay my own design page. Is it possible? Please Help me. And this is code that i followed import java.io.IOException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.google.appengine.api.users.UserService; import com.google.appengine.api.users.UserServiceFactory; import com.google.appengine.api.users.User; public class New extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException { resp.setHeader("Cache-Control", "no-store, no-cache, must-revalidate"); resp.setContentType("text/html"); UserService userService = UserServiceFactory.getUserService(); User user = userService.getCurrentUser(); if (user != null) { if(user.getEmail().equals("[email protected]")) { resp.getWriter().println("done"); resp.sendRedirect("/login.jsp"); } else { resp.getWriter().println("Hello, " + user.getNickname()+"<br>"); resp.getWriter().println("Thanks for your interest. But this application is still not available to everybody."); resp.getWriter().println("<a href="+UserServiceFactory.getUserService().createLogoutURL(userService.createLoginURL(req.getRequestURI()))+">Log out</a>"); } } else { resp.sendRedirect(userService.createLoginURL("http://mail.yyy.edu.in")); } } } Thanks in advance Regards Sharun.

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  • WPF: How to bind and update display with DataContext

    - by Am
    I'm trying to do the following thing: I have a TabControl with several tabs. Each TabControlItem.Content points to PersonDetails which is a UserControl Each BookDetails has a dependency property called IsEditMode I want a control outside of the TabControl , named ToggleEditButton, to be updated whenever the selected tab changes. I thought I could do this by changing the ToggleEditButton data context, by it doesn't seem to work (but I'm new to WPF so I might way off) The code changing the data context: private void tabControl1_SelectionChanged(object sender, SelectionChangedEventArgs e) { if (e.Source is TabControl) { if (e.Source.Equals(tabControl1)) { if (tabControl1.SelectedItem is CloseableTabItem) { var tabItem = tabControl1.SelectedItem as CloseableTabItem; RibbonBook.DataContext = tabItem.Content as BookDetails; ribbonBar.SelectedTabItem = RibbonBook; } } } } The DependencyProperty under BookDetails: public static readonly DependencyProperty IsEditModeProperty = DependencyProperty.Register("IsEditMode", typeof (bool), typeof (BookDetails), new PropertyMetadata(true)); public bool IsEditMode { get { return (bool)GetValue(IsEditModeProperty); } set { SetValue(IsEditModeProperty, value); SetValue(IsViewModeProperty, !value); } } And the relevant XAML: <odc:RibbonTabItem Title="Book" Name="RibbonBook"> <odc:RibbonGroup Title="Details" Image="img/books2.png" IsDialogLauncherVisible="False"> <odc:RibbonToggleButton Content="Edit" Name="ToggleEditButton" odc:RibbonBar.MinSize="Medium" SmallImage="img/edit_16x16.png" LargeImage="img/edit_32x32.png" Click="Book_EditDetails" IsChecked="{Binding Path=IsEditMode, Mode=TwoWay}"/> ... There are two things I want to accomplish, Having the button reflect the IsEditMode for the visible tab, and have the button change the property value with no code behind (if posible) Any help would be greatly appriciated.

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  • Disposing ActiveX resources owned by another thread

    - by Stefan Teitge
    I've got a problem problem with threading and disposing resources. I've got a C# Windows Forms application which runs expensive operation in a thread. This thread instantiates an ActiveX control (AxControl). This control must be disposed as it uses a high amount of memory. So I implemented a Dispose() method and even a destructor. After the thread ends the destructor is called. This is sadly called by the UI thread. So invoking activexControl.Dispose(); fails with the message "COM object that has been separated from its underlying RCW", as the object belongs to another thread. How to do this correctly or is it just a bad design I use? (I stripped the code down to the minimum including removing any safety concerns.) class Program { [STAThread] static void Main() { // do stuff here, e.g. open a form new Thread(new ThreadStart(RunStuff); // do more stuff } private void RunStuff() { DoStuff stuff = new DoStuff(); stuff.PerformStuff(); } } class DoStuff : IDisposable { private AxControl activexControl; DoStuff() { activexControl = new AxControl(); activexControl.CreateControl(); // force instance } ~DoStuff() { Dispose(); } public void Dispose() { activexControl.Dispose(); } public void PerformStuff() { // invent perpetuum mobile here, takes time } }

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  • Immutable classes in C++

    - by ereOn
    Hi, In one of my projects, I have some classes that represent entities that cannot change once created, aka. immutable classes. Example : A class RSAKey that represent a RSA key which only has const methods. There is no point changing the existing instance: if you need another one, you just create one. My objects sometimes are heavy and I enforced the use of smart pointers to avoid copy. So far, I have the following pattern for my classes: class RSAKey : public boost::noncopyable, public boost::enable_shared_from_this<RSAKey> { public: /** * \brief Some factory. * \param member A member value. * \return An instance. */ static boost::shared_ptr<const RSAKey> createFromMember(int member); /** * \brief Get a member. * \return The member. */ int getMember() const; private: /** * \brief Constructor. * \param member A member. */ RSAKey(int member); /** * \brief Member. */ const int m_member; }; So you can only get a pointer (well, a smart pointer) to a const RSAKey. To me, it makes sense, because having a non-const reference to the instance is useless (it only has const methods). Do you guys see any issue regarding this pattern ? Are immutable classes something common in C++ or did I just created a monster ? Thank you for your advices !

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  • What's the most DRY-appropriate way to execute an SQL command?

    - by Sean U
    I'm looking to figure out the best way to execute a database query using the least amount of boilerplate code. The method suggested in the SqlCommand documentation: private static void ReadOrderData(string connectionString) { string queryString = "SELECT OrderID, CustomerID FROM dbo.Orders;"; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlCommand command = new SqlCommand(queryString, connection); connection.Open(); SqlDataReader reader = command.ExecuteReader(); try { while (reader.Read()) { Console.WriteLine(String.Format("{0}, {1}", reader[0], reader[1])); } } finally { reader.Close(); } } } mostly consists of code that would have to be repeated in every method that interacts with the database. I'm already in the habit of factoring out the establishment of a connection, which would yield code more like the following. (I'm also modifying it so that it returns data, in order to make the example a bit less trivial.) private SQLConnection CreateConnection() { var connection = new SqlConnection(_connectionString); connection.Open(); return connection; } private List<int> ReadOrderData() { using(var connection = CreateConnection()) using(var command = connection.CreateCommand()) { command.CommandText = "SELECT OrderID FROM dbo.Orders;"; using(var reader = command.ExecuteReader()) { var results = new List<int>(); while(reader.Read()) results.Add(reader.GetInt32(0)); return results; } } } That's an improvement, but there's still enough boilerplate to nag at me. Can this be reduced further? In particular, I'd like to do something about the first two lines of the procedure. I don't feel like the method should be in charge of creating the SqlCommand. It's a tiny piece of repetition as it is in the example, but it seems to grow if transactions are being managed manually or timeouts are being altered or anything like that.

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  • Time with and without OpenMP

    - by was
    I have a question.. I tried to improve a well known program algorithm in C, FOX algorithm for matrix multiplication.. relative link without openMP: (http://web.mst.edu/~ercal/387/MPI/ppmpi_c/chap07/fox.c). The initial program had only MPI and I tried to insert openMP in the matrix multiplication method, in order to improve the time of computation: (This program runs in a cluster and computers have 2 cores, thus I created 2 threads.) The problem is that there is no difference of time, with and without openMP. I observed that using openMP sometimes, time is equivalent or greater than the time without openMP. I tried to multiply two 600x600 matrices. void Local_matrix_multiply( LOCAL_MATRIX_T* local_A /* in */, LOCAL_MATRIX_T* local_B /* in */, LOCAL_MATRIX_T* local_C /* out */) { int i, j, k; chunk = CHUNKSIZE; // 100 #pragma omp parallel shared(local_A, local_B, local_C, chunk, nthreads) private(i,j,k,tid) num_threads(2) { /* tid = omp_get_thread_num(); if(tid == 0){ nthreads = omp_get_num_threads(); printf("O Pollaplasiamos pinakwn ksekina me %d threads\n", nthreads); } printf("Thread %d use the matrix: \n", tid); */ #pragma omp for schedule(static, chunk) for (i = 0; i < Order(local_A); i++) for (j = 0; j < Order(local_A); j++) for (k = 0; k < Order(local_B); k++) Entry(local_C,i,j) = Entry(local_C,i,j) + Entry(local_A,i,k)*Entry(local_B,k,j); } //end pragma omp parallel } /* Local_matrix_multiply */

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  • Why does first call to java.io.File.createTempFile(String,String,File) take 5 seconds on Citrix?

    - by Ben Roling
    While debugging slow startup of an Eclipse RCP app on a Citrix server, I came to find out that java.io.createTempFile(String,String,File) is taking 5 seconds. It does this only on the first execution and only for certain user accounts. Specifically, I am noticing it Citrix anonymous user accounts. I have not tried many other types of accounts, but this behavior is not exhibited with an administrator account. Also, it does not matter if the user has access to write to the given directory or not. If the user does not have access, the call will take 5 seconds to fail. If they do have access, the call with take 5 seconds to succeed. This is on a Windows 2003 Server. I've tried Sun's 1.6.0_16 and 1.6.0_19 JREs and see the same behavior. I googled a bit expecting this to be some sort of known issue, but didn't find anything. It seems like someone else would have had to have run into this before. The Eclipse Platform uses File.createTempFile() to test various directories to see if they are writeable during initialization and this issue adds 5 seconds to the startup time of our application. I imagine somebody has run into this before and might have some insight. Here is sample code I executed to see that it is indeed this call that is consuming the time. I also tried it with a second call to createTempFile and notice that subsequent calls return nearly instantaneously. public static void main(final String[] args) throws IOException { final File directory = new File(args[0]); final long startTime = System.currentTimeMillis(); File file = null; try { file = File.createTempFile("prefix", "suffix", directory); System.out.println(file.getAbsolutePath()); } finally { System.out.println(System.currentTimeMillis() - startTime); if (file != null) { file.delete(); } } } Sample output of this program is the following: C:\java.exe -jar filetest.jar C:/Temp C:\Temp\prefix8098550723198856667suffix 5093

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  • How to handle not-enough-isolatedstorage issue deep in data loader?

    - by Edward Tanguay
    I have a silverlight application which loads data from many external data sources into IsolatedStorage, and while loading any of these sources if it does not have enough IsolatedStorage, it ends up in a catch statement. At that point in that catch statement I would like to ask the user to click a button to approve silverlight to increase the IsolatedStorage capacity. The problem is, although I have a "SwitchPage()" method with which I display a page, if I access it at this point it is too deep in the loading process and the application always goes into an endless loop, hangs and crashes. I need a way to branch out of the application completely somehow to an independent UserControl which has a button and code behind which does the increase logic. What is a solution for an application to be able to branch out of a loading process catch statement like this, display a user control which has a button to ask the user to increase the IsolatedStorage? public static void SaveBitmapImageToIsolatedStorageFile(OpenReadCompletedEventArgs e, string fileName) { try { using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication()) { using (IsolatedStorageFileStream isfs = new IsolatedStorageFileStream(fileName, FileMode.Create, isf)) { Int64 imgLen = (Int64)e.Result.Length; byte[] b = new byte[imgLen]; e.Result.Read(b, 0, b.Length); isfs.Write(b, 0, b.Length); isfs.Flush(); isfs.Close(); isf.Dispose(); } } } catch (IsolatedStorageException) { //handle: present user with button to increase isolated storage } catch (TargetInvocationException) { //handle: not saved } }

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  • Parameterized SPARQL query with JENA

    - by sandra
    I'm trying to build a small semantic web application using Jena framework, JSP and JAVA. I have a remote SPARQL endpoint and I've already written a simple query which works fine but now I need to use some parameters. Here is my code so far: final static String serviceEndpoint = "http://fishdelish.cs.man.ac.uk/sparql/"; String comNameQuery = "PREFIX fd: <http://fishdelish.cs.man.ac.uk/rdf/vocab/resource/> " + "SELECT ?name ?language ?type" + "WHERE { ?nameID fd:comnames_ComName ?name ;" + "fd:comnames_Language ?language ;" + "fd:comnames_NameType ?type ." + "}"; Query query = QueryFactory.create(comNameQuery); QueryExecution qe = QueryExecutionFactory.sparqlService(serviceEndpoint,query); try { ResultSet rs = qe.execSelect(); if ( rs.hasNext() ) { System.out.println(ResultSetFormatter.asText(rs)); } } catch(Exception e) { System.out.println(e.getMessage()); } finally { qe.close(); } What I want to do is to parameterized ?name. I'm new to Jena and I'm not really sure how to use parameters in a SPARQL query. I would appreciate it if someone could help me with this.

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