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• Generics not so generic !!

  - by Aymen

  Hi I tried to implement a generic binary search algorithm in scala. Here it is : type Ord ={ def <(x:Any):Boolean def >(x:Any):Boolean } def binSearch[T <: Ord ](x:T,start:Int,end:Int,t:Array[T]):Boolean = { if (start > end) return false val pos = (start + end ) / 2 if(t(pos)==x) true else if (t(pos) < x) binSearch(x,pos+1,end,t) else binSearch(x,start,pos-1,t) } everything is OK until I tried to actually use it (xD) : binSearch(3,0,4,Array(1,2,5,6)) the compiler is pretending that Int not a member of Ord, well what shall I do to solve this ? Thanks

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• Exécutez des applications vintage sur votre navigateur grâce à Historical Software Collection, un projet de l'Internet Archive

  Exécutez des applications vintage sur votre navigateur grâce à Historical Software Collection, Un projet de l'Internet Archive La Historical Software Collection est un clin d'oeil aux applications des années 80. Une invite d'Internet Archive a se replonger dans son enfance pour certains le temps d'une partie de jeu vidéo. D'autres y verront une occasion de constater l'évolution technologique de ces 30 dernières années.Grâce à JMESS, un portage de l'émulateur MESS (Multi Emulator Super System)...

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• iTextSharp error - cannot convert type 'Collections.Generic.List' to 'iTextSharp.text.Element'

  - by mike

  I am trying to export pdf file using aspx and c#. I got the following error. Cannot implicitly convert type 'System.Collections.Generic.List'' to 'iTextSharp.text.Element' I have the following code using iTextSharp.text; using iTextSharp.text.pdf; using iTextSharp.text.html.simpleparser; StringBuilder strB = new StringBuilder(); document.Open(); if (text.Length.Equals(0))//export the text { GridView1.DataBind(); using (StringWriter sWriter = new StringWriter(strB)) { using (HtmlTextWriter htWriter = new HtmlTextWriter(sWriter)) { GridView1.RenderControl(htWriter); } } } else //export the grid { strB.Append(text); } using (TextReader sReader = new StringReader(strB.ToString())) { StyleSheet styles = new StyleSheet(); List<Element> list = new List<Element>(); list = HTMLWorker.ParseToList(sReader, styles); foreach (IElement elm in list) { document.Add(elm); } } I got the error in this line: list = HTMLWorker.ParseToList(sReader, styles); It's the first time that I am trying to export pdf files. I tried to cast the list element , however this did not solve my error. Any advice would be helpful!!!

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• Spring 3 DI using generic DAO interface

  - by Peders

  I'm trying to use @Autowired annotation with my generic Dao interface like this: public interface DaoContainer<E extends DomainObject> { public int numberOfItems(); // Other methods omitted for brevity } I use this interface in my Controller in following fashion: @Configurable public class HelloWorld { @Autowired private DaoContainer<Notification> notificationContainer; @Autowired private DaoContainer<User> userContainer; // Implementation omitted for brevity } I've configured my application context with following configuration <context:spring-configured /> <context:component-scan base-package="com.organization.sample"> <context:exclude-filter expression="org.springframework.stereotype.Controller" type="annotation" /> </context:component-scan> <tx:annotation-driven /> This works only partially, since Spring creates and injects only one instance of my DaoContainer, namely DaoContainer. In other words, if I ask userContainer.numberOfItems(); I get the number of notificationContainer.numberOfItems() I've tried to use strongly typed interfaces to mark the correct implementation like this: public interface NotificationContainer extends DaoContainer<Notification> { } public interface UserContainer extends DaoContainer<User> { } And then used these interfaces like this: @Configurable public class HelloWorld { @Autowired private NotificationContainer notificationContainer; @Autowired private UserContainer userContainer; // Implementation omitted... } Sadly this fails to BeanCreationException: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.organization.sample.dao.NotificationContainer com.organization.sample.HelloWorld.notificationContainer; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.organization.sample.NotificationContainer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} Now, I'm a little confused how should I proceed or is using multiple Dao's even possible. Any help would be greatly appreciated :)

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• Filter a wpf collectionviewsource in VB?

  - by Johnny Westlake

  Hi, I want to filter a collectionviewsource using a filter I've written, but I'm not sure how I can apply the filter to it? Here is my collection view source: <Grid.Resources> <CollectionViewSource x:Key="myCollectionView" Source="{Binding Path=Query4, Source={x:Static Application.Current}}"> <CollectionViewSource.SortDescriptions> <scm:SortDescription PropertyName="ContactID" Direction="Descending"/> </CollectionViewSource.SortDescriptions> </CollectionViewSource> </Grid.Resources> I have implemented a filter as such: Private Sub WorkerFilter(ByVal sender As Object, ByVal e As FilterEventArgs) Dim value As Object = CType(e.Item, System.Data.DataRow)("StaffSection") If (Not value Is Nothing) And (Not value Is DBNull.Value) Then If (value = "Builder") Or (value = "Office Staff") Then e.Accepted = True Else e.Accepted = False End If End If End Sub So how can I get the CollectionViewSource filtered by the filter on load? Could you please give all hte code I need (only a few lines I figure) as I'm quite new to coding. Thanks guys EDIT: For the record, <CollectionViewSource x:Key="myCollectionView" Filter="WorkerFilter" ... /> gives me the error: Failed object initialization (ISupportInitialize.EndInit). 'System.Windows.Data.BindingListCollectionView' view does not support filtering. Error at object 'myCollectionView'

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• Performance penalty of typecasting and boxing/unboxing types in C# when storing generic values

  - by kitsune

  I have a set-up similar to WPF's DependencyProperty and DependencyObject system. My properties however are generic. A BucketProperty has a static GlobalIndex (defined in BucketPropertyBase) which tracks all BucketProperties. A Bucket can have many BucketProperties of any type. A Bucket saves and gets the actual values of these BucketProperties... now my question is, how to deal with the storage of these values, and what is the penalty of using a typecasting when retrieving them? I currently use an array of BucketEntries that save the property values as simple objects. Is there any better way of saving and returning these values? Beneath is a simpliefied version: public class BucketProperty<T> : BucketPropertyBase { } public class Bucket { private BucketEntry[] _bucketEntries; public void SaveValue<T>(BucketProperty<T> property, T value) { SaveBucketEntry(property.GlobalIndex, value) } public T GetValue<T>(BucketProperty<T> property) { return (T)FindBucketEntry(property.GlobalIndex).Value; } } public class BucketEntry { private object _value; private uint _index; public BucketEntry(uint globalIndex, object value) { ... } }

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• Creating A Single Generic Handler For Agatha?

  - by David

  I'm using the Agatha request/response library (and StructureMap, as utilized by Agatha 1.0.5.0) for a service layer that I'm prototyping, and one thing I've noticed is the large number of handlers that need to be created. It generally makes sense that any request/response type pair would need their own handler. However, as this scales to a large enterprise environment that's going to be A LOT of handlers. What I've started doing is dividing up the enterprise domain into logical processor classes (dozens of processors instead of many hundreds or possibly eventually thousands handlers). The convention is that each request/response type (all of which inherit from a domain base request/response pair, which inherit from Agatha's) gets exactly one function in a processor somewhere. The generic handler (which inherits from Agatha's RequestHandler) then uses reflection in the Handle method to find the method for the given TREQUEST/TRESPONSE and invoke it. If it can't find one or if it finds more than one, it returns a TRESPONSE containing an error message (messages are standardized in the domain's base response class). The goal here is to allow developers across the enterprise to just concern themselves with writing their request/response types and processor functions in the domain and not have to spend additional overhead creating handler classes which would all do exactly the same thing (pass control to a processor function). However, it seems that I still need to have defined a handler class (albeit empty, since the base handler takes care of everything) for each request/response type pair. Otherwise, the following exception is thrown when dispatching a request to the service: StructureMap Exception Code: 202 No Default Instance defined for PluginFamily Agatha.ServiceLayer.IRequestHandler`1[[TSFG.Domain.DTO.Actions.HelloWorldRequest, TSFG.Domain.DTO, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]], Agatha.ServiceLayer, Version=1.0.5.0, Culture=neutral, PublicKeyToken=6f21cf452a4ffa13 Is there a way that I'm not seeing to tell StructureMap and/or Agatha to always use the base handler class for all request/response type pairs? Or maybe to use Reflection.Emit to generate empty handlers in memory at application start just to satisfy the requirement? I'm not 100% familiar with these libraries and am learning as I go along, but so far my attempts at both those possible approaches have been unsuccessful. Can anybody offer some advice on solving this, or perhaps offer another approach entirely?

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• How do I debug a crash when I run my garbage-collected app in Rosetta?

  - by Rob Keniger

  I have a Universal app which is targeting 10.5 and which uses garbage collection. I am building for ppc, i386 and x86_64. I don't have access to a physical PowerPC machine so I am trying to use Rosetta to confirm that the PowerPC portion of the app works correctly. However, as soon as the app is launched in Rosetta it immediately crashes with the following crash log: Process: FooApp [91567] Path: /Users/rob/Development/src/FooApp/build/Release 64-bit/FooApp.app/Contents/MacOS/FooApp Identifier: com.companyX.FooApp Version: 0.9 (build d540e05) (2) Code Type: PPC (Translated) Parent Process: launchd [708] Date/Time: 2010-04-09 18:32:23.962 +1000 OS Version: Mac OS X 10.6.3 (10D573) Report Version: 6 Exception Type: EXC_CRASH (SIGTRAP) Exception Codes: 0x0000000000000000, 0x0000000000000000 Crashed Thread: 5 ...snip non-relevant threads... Thread 5 Crashed: 0 libSystem.B.dylib 0x8023656a __pthread_kill + 10 1 libSystem.B.dylib 0x80235e17 pthread_kill + 95 2 com.companyX.FooApp 0xb80bfb30 0xb8000000 + 785200 3 com.companyX.FooApp 0xb80c0037 0xb8000000 + 786487 4 com.companyX.FooApp 0xb80dd8e8 0xb8000000 + 907496 5 com.companyX.FooApp 0xb8145397 spin_lock_wrapper + 1791 6 com.companyX.FooApp 0xb801ceb7 0xb8000000 + 118455 I have used the Apple docs on debugging translated apps and the information on this page to attach gdb to the app when it's running in Rosetta. The app immediately breaks into the debugger upon launch: Program received signal SIGTRAP, Trace/breakpoint trap. [Switching to thread 15107] 0x9151fdd4 in auto_fatal () (gdb) bt #0 0x9151fdd4 in auto_fatal () #1 0x91536d84 in Auto::Thread::get_register_state () #2 0x915372f8 in Auto::Thread::scan_other_thread () #3 0x91529be4 in Auto::Zone::scan_registered_threads () #4 0x91539114 in Auto::MemoryScanner::scan_thread_ranges () #5 0x9153b000 in Auto::MemoryScanner::scan () #6 0x9153049c in Auto::Zone::collect () #7 0x915198f4 in auto_collect_internal () #8 0x9151a094 in auto_collection_work () #9 0x96687434 in _dispatch_call_block_and_release () #10 0x9668912c in _dispatch_queue_drain () #11 0x96689350 in _dispatch_queue_invoke () #12 0x966895c0 in _dispatch_worker_thread2 () #13 0x966896fc in _dispatch_worker_thread () #14 0x965a97e8 in _pthread_body () (gdb) I have no idea where to start with this. It looks like the Garbage Collector is failing very badly. Are garbage-collected PowerPC apps not supported in Rosetta? I can't see any mention of this limitation in the docs if so. Does anyone have any ideas?

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• Structuremap and generic types

  - by James D

  Hi I have a situation which seems a bit different from others I've seen. For clarrification, this isn't the normal question eg; something like IAClass maps to AClass etc - that involves using basically a single concrete classes per interface. This involves having a single generic class, but I want to be able to load ALL possible usages of it. Eg - the main class is of public class MyClass<TDomainObject> : IMyClass<TDomainObject> where TDomainObject : DomainObject So example usages would be IMyClass<Person> p = new MyClass<Person>; IMyClass<Employer> p = new MyClass<Employer>; I.e. for all DomainObjects I would like to be able to load a MyClass< for. So you can see I don't use a specific class for each declaration, they all use the same one. How would I get this loaded into StructureMap?

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• Deserialize generic collections - coming up empty

  - by AC

  I've got a settings object for my app that has two collections in it. The collections are simple List generics that contain a collection of property bags. When I serialize it, everything is saved with no problem: XmlSerializer x = new XmlSerializer(settings.GetType()); TextWriter tw = new StreamWriter(@"c:\temp\settings.cpt"); x.Serialize(tw, settings); However when I deserialize it, everything is restored except for the two collections (verified by setting a breakpoint on the setters: XmlSerializer x = new XmlSerializer(typeof(CourseSettings)); XmlReader tr = XmlReader.Create(@"c:\temp\settings.cpt"); this.DataContext = (CourseSettings)x.Deserialize(tr); What would cause this? Everything is pretty vanilla... here's a snippet from the settings object... omitting most of it. The PresentationSourceDirectory works just fine, but the PresentationModules' setter isn't hit: private string _presentationSourceDirectory = string.Empty; public string PresentationSourceDirectory { get { return _presentationSourceDirectory; } set { if (_presentationSourceDirectory != value) { OnPropertyChanged("PresentationSourceDirectory"); _presentationSourceDirectory = value; } } } private List<Module> _presentationModules = new List<Module>(); public List<Module> PresentationModules { get { var sortedModules = from m in _presentationModules orderby m.ModuleOrder select m; return sortedModules.ToList<Module>(); } set { if (_presentationModules != value) { _presentationModules = value; OnPropertyChanged("PresentationModules"); } } }

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• A generic error in GDI+ with ToolStrip in ManagerRenderMode

  - by volody

  I have a vb.net form with ToolStrip menu RenderMode - ManagerRenderMode LayoutStyle - HorizontalStackWithOverflow My development environment is .net 4.0, VS2010, windows 7 x64; but occasionally I am getting next error A generic error occurred in GDI+. Stacktrace: at System.Drawing.Graphics.CheckErrorStatus(Int32 status) at System.Drawing.Graphics.FillRectangle(Brush brush, Int32 x, Int32 y, Int32 width, Int32 height) at System.Drawing.Graphics.FillRectangle(Brush brush, Rectangle rect) at System.Windows.Forms.ToolStripProfessionalRenderer.FillWithDoubleGradient(Color beginColor, Color middleColor, Color endColor, Graphics g, Rectangle bounds, Int32 firstGradientWidth, Int32 secondGradientWidth, LinearGradientMode mode, Boolean flipHorizontal) at System.Windows.Forms.ToolStripProfessionalRenderer.RenderToolStripBackgroundInternal(ToolStripRenderEventArgs e) at System.Windows.Forms.ToolStripProfessionalRenderer.OnRenderToolStripBackground(ToolStripRenderEventArgs e) at System.Windows.Forms.ToolStripRenderer.DrawToolStripBackground(ToolStripRenderEventArgs e) at System.Windows.Forms.ToolStrip.OnPaintBackground(PaintEventArgs e) at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer) at System.Windows.Forms.Control.WmPaint(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.ScrollableControl.WndProc(Message& m) at System.Windows.Forms.ToolStrip.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

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• Marshalling a big-endian byte collection into a struct in order to pull out values

  - by Pat

  There is an insightful question about reading a C/C++ data structure in C# from a byte array, but I cannot get the code to work for my collection of big-endian (network byte order) bytes. (EDIT: Note that my real struct has more than just one field.) Is there a way to marshal the bytes into a big-endian version of the structure and then pull out the values in the endianness of the framework (that of the host, which is usually little-endian)? This should summarize what I'm looking for (LE=LittleEndian, BE=BigEndian): void Main() { var leBytes = new byte[] {1, 0}; var beBytes = new byte[] {0, 1}; Foo fooLe = ByteArrayToStructure<Foo>(leBytes); Foo fooBe = ByteArrayToStructureBigEndian<Foo>(beBytes); Assert.AreEqual(fooLe, fooBe); } [StructLayout(LayoutKind.Explicit, Size=2)] public struct Foo { [FieldOffset(0)] public ushort firstUshort; } T ByteArrayToStructure<T>(byte[] bytes) where T: struct { GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned); T stuff = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(),typeof(T)); handle.Free(); return stuff; } T ByteArrayToStructureBigEndian<T>(byte[] bytes) where T: struct { ??? }

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• Formula parsing / evaluation routine or library with generic DLookup functionality

  - by tbone

  I am writing a .Net application where I must support user-defined formulas that can perform basic mathematics, as well as accessing data from any arbitrary table in the database. I have the math part working, using JScript Eval(). What I haven't decided on is what a nice way is to do the generic table lookups. For example, I may have a formula something like: Column: BonusAmount Formula: {CurrentSalary} * 1.5 * {[SystemSettings][Value][SettingName=CorpBonus AND Year={Year}]} So, in this example I would replace {xxx} and {Year} with the value of Column xxx from the current table, and I would replace the second part with the value of (select Value from SystemSettings WHERE SettingName='CorpBonus' AND Year=2008) So, basically, I am looking for something very much like the MS Access DLookup function: DLookup ( expression, domain, [criteria] ) DLookup("[UnitPrice]", "Order Details", "OrderID = 10248") But, I also need to overall parsing routine that can tell whether to just look up in the current row, or to look into another table. Would also be nice to support aggregate functions (ie: DAvg, DMax, etc), as well as all the weird edge cases handled. So I wonder if anyone knows of any sort of an existing library, or has a nice routine that can handle this formula parsing and database lookup / aggregate function resolution requirements.

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• How do I expose the columns collection of GridView control that is inside a user control

  - by Christopher Edwards

  See edit. I want to be able to do this in the aspx that consumes the user control. <uc:MyControl ID="MyGrid" runat="server"> <asp:BoundField DataField="FirstColumn" HeaderText="FirstColumn" /> <asp:BoundField DataField="SecondColumn" HeaderText="SecondColumn" /> </uc> I have this code (which doesn't work). Any ideas what I am doing wrong? VB Partial Public Class MyControl Inherits UserControl <System.Web.UI.IDReferenceProperty(GetType(DataControlFieldCollection))> _ Public Property Columns() As DataControlFieldCollection Get Return MyGridView.Columns End Get Set(ByVal value As DataControlFieldCollection) ' The Columns collection of the GridView is ReadOnly, so I rebuild it MyGridView.Columns.Clear() For Each c As DataControlField In value MyGridView.Columns.Add(c) Next End Set End Property ... End Class C# public partial class MyControl : UserControl {         [System.Web.UI.IDReferenceProperty(typeof(DataControlFieldCollection))]     public DataControlFieldCollection Columns {         get { return MyGridView.Columns; }         set {             MyGridView.Columns.Clear();             foreach (DataControlField c in value) {                 MyGridView.Columns.Add(c);             }         }     } ... } EDIT: Actually it does work, but auto complete does not work between the uc:MyControl opening and closing tags and I get compiler warnings:- Content is not allowed between the opening and closing tags for element 'MyControl'. Validation (XHTML 1.0 Transitional): Element 'columns' is not supported. Element 'BoundField' is not a known element. This can occur if there is a compilation error in the Web site, or the web.config file is missing. So I guess I need to use some sort of directive to tell the complier to expect content between the tags. Any ideas?

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• Generic allocator class without variadic templates?

  - by rainer

  I am trying to write a generic allocator class that does not really release an object's memory when it is free()'d but holds it in a queue and returns a previously allocated object if a new one is requested. Now, what I can't wrap my head around is how to pass arguments to the object's constructor when using my allocator (at least without resorting to variadic templates, that is). The alloc() function i came up with looks like this: template <typename... T> inline T *alloc(const &T... args) { T *p; if (_free.empty()) { p = new T(args...); } else { p = _free.front(); _free.pop(); // to call the ctor of T, we need to first call its DTor p->~T(); p = new( p ) T(args...); } return p; } Still, I need the code to be compatible with today's C++ (and older versions of GCC that do not support variadic templates). Is there any other way to go about passing an arbitrary amount of arguments to the objects constructor?

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• WPF Designer has bug with parsing generic control with overrided property

  - by Ivan Laktyunkin

  I've created a generic lookless control with virtual property: public abstract class TestControlBase<TValue> : Control { public static readonly DependencyProperty ValueProperty; static TestControlBase() { ValueProperty = DependencyProperty.Register("Value", typeof(TValue), typeof(TestControlBase<TValue>)); } protected TestControlBase() { Focusable = false; Value = default(TValue); } public virtual TValue Value { get { return (TValue)GetValue(ValueProperty); } set { SetValue(ValueProperty, value); } } } Then I've made a control derived from it and overrided Value property: public class TestControl : TestControlBase<int> { public override int Value { get { return base.Value; } set { base.Value = value; } } } So I use it in a Window XAML: <TestControls:TestControl /> When I open window in designer all is OK, but when I put mouse cursor to this line, or to this control in designer I receive exception: Exception has been thrown by the target of an invocation. at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Delegate.DynamicInvokeImpl(Object[] args) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) Ambiguous match found. at System.RuntimeType.GetPropertyImpl(String name, BindingFlags bindingAttr, Binder binder, Type returnType, Type[] types, ParameterModifier[] modifiers) at System.Type.GetProperty(String name) at MS.Internal.ComponentModel.DependencyPropertyKind.get_IsDirect() at MS.Internal.ComponentModel.DependencyPropertyKind.get_IsAttached() at MS.Internal.ComponentModel.APCustomTypeDescriptor.GetProperties(Attribute[] attributes) at MS.Internal.ComponentModel.APCustomTypeDescriptor.GetProperties() at System.ComponentModel.TypeDescriptor.TypeDescriptionNode.DefaultExtendedTypeDescriptor.System.ComponentModel.ICustomTypeDescriptor.GetProperties() at System.ComponentModel.TypeDescriptor.GetPropertiesImpl(Object component, Attribute[] attributes, Boolean noCustomTypeDesc, Boolean noAttributes) at System.ComponentModel.TypeDescriptor.GetProperties(Object component) at MS.Internal.Model.ModelPropertyCollectionImpl.GetProperties(String propertyNameHint) at MS.Internal.Model.ModelPropertyCollectionImpl.<GetEnumerator>d__0.MoveNext() at MS.Internal.Designer.PropertyEditing.Model.ModelPropertyMerger.<GetFirstProperties>d__0.MoveNext() at MS.Internal.Designer.PropertyEditing.PropertyInspector.UpdateCategories(Selection selection) at MS.Internal.Designer.PropertyEditing.PropertyInspector.OnSelectionChangedIdle() Who know this problem? Please explain :) I have no ideas except that WPF Designer doesn't like generics. If I replace generics by Object all is OK.

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• Using LINQ in generic collections

  - by Hugo S Ferreira

  Hi, Please consider the following snippet from an implementation of the Interpreter pattern: public override object Execute(Interpreter interpreter, object ctx) { var list = ctx as IEnumerable<string>; return (list != null) ? list.FirstOrDefault() : null; } What about if I want to use the same function for integers? public override object Execute(Interpreter interpreter, object ctx) { var list = ctx as IEnumerable<string>; if (list != null) return list.FirstOrDefault(); var list = ctx as IEnumerable<int>; return (list != null) ? list.FirstOrDefault() : null; } What I wanted was something like: public override object Execute(Interpreter interpreter, object ctx) { var list = ctx as IEnumerable; return (list != null) ? list.FirstOrDefault() : null; } But Linq doesn't act on IEnumerables. Instead, to get to this solution, I would be forced to write something like: public override object Execute(Interpreter interpreter, object ctx) { var list = ctx as IEnumerable; if (list != null) foreach(var i in list) { yield return i; return; } return null; } Or use a generic method: public override T Execute<T>(Interpreter interpreter, object ctx) { var list = ctx as IEnumerable<T>; return (list != null) ? list.FirstOrDefault() : null; } Which would break the Interpreter pattern (as it was implemented in this system). Covariance would also fail (at least in C#3), though would it work, it would be the exact behavior I wanted: public override object Execute(Interpreter interpreter, object ctx) { var list = ctx as IEnumerable<object>; return (list != null) ? list.FirstOrDefault() : null; } So, my question is: what's the best way to achieve the intended behavior? Thanks :-)

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• Java Collections and Garbage Collector

  - by Anth0

  A little question regarding performance in a Java web app. Let's assume I have a List<Rubrique> listRubriques with ten Rubrique objects. A Rubrique contains one list of products (List<product> listProducts) and one list of clients (List<Client> listClients). What exactly happens in memory if I do this: listRubriques.clear(); listRubriques = null; My point of view would be that, since listRubriques is empty, all my objects previously referenced by this list (including listProducts and listClients) will be garbage collected pretty soon. But since Collection in Java are a little bit tricky and since I have quite performance issues with my app i'm asking the question :) edit : let's assume now that my Client object contains a List<Client>. Therefore, I have kind of a circular reference between my objects. What would happen then if my listRubrique is set to null? This time, my point of view would be that my Client objects will become "unreachable" and might create a memory leak?

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• How to simply a foreach iteration using reflection

  - by Priya

  Consider that I have to get the overall performance of X. X has Y elements and Y in turn has Z elements which inturn has some N elements. To get the performance of X I do this: List<double> XQ = new List<double>(); foreach (Elem Y in X.Y){ List<double> YQ = new List<double>(); foreach (Elem Z in Y.Z){ List<double> ZQ = new List<double>(); foreach (Elem N in Z.N){ ZQ.Add(GetPerformance(N)); } YQ.Add(AVG(ZQ)); } XQ.Add(AVG(YQ)); } AVG of XQ list gives the performance of X. The performance can be calculated for either X or Y or for Z. X, Y and Z share the same base class. So depending on the item given the foreach loop has to be executed. Currently I have a switch case to determine each item (X or Y or Z) and the foreach loop is repeated in the code pertaining to the item (eg. If Y foreach starts from Y.Z). Is is possible to convert this whole code generic using reflection instead of having to repeat it in each switch case? Thanks

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• Why is it a bad practice to call System.gc?

  - by zneak

  After answering to a question about how to force-free objects in Java (the guy was clearing a 1.5GB HashMap) with System.gc(), I've been told it's a bad practice to call System.gc() manually, but the comments seemed mitigated about it. So much that no one dared to upvote it, nor downvote it. I've been told there it's a bad practice, but then I've also been told garbage collector runs don't systematically stop the world anymore, and that it could also be only seen as a hint, so I'm kind of at loss. I do understand that usually the JVM knows better than you when it needs to reclaim memory. I also understand that worrying about a few kilobytes of data is silly. And I also understand that even megabytes of data isn't what it was a few years back. But still, 1.5 gigabyte? And you know there's like 1.5 GB of data hanging around in memory; it's not like it's a shot in the dark. Is System.gc() systematically bad, or is there some point at which it becomes okay? So the question is actually double: Why is it or not a bad practice to call System.gc()? Is it really a hint under certain implementations, or is it always a full collection cycle? Are there really garbage collector implementations that can do their work without stopping the world? Please shed some light over the various assertions people have made. Where's the threshold? Is it never a good idea to call System.gc(), or are there times when it's acceptable? If any, what are those times?

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• Create Generic method constraining T to an Enum

  - by johnc

  I'm building a function to extend the Enum.Parse concept that allows a default value to be parsed in case that an Enum value is not found Is case insensitive So I wrote the following public static T GetEnumFromString<T>(string value, T defaultValue) where T : Enum { if (string.IsNullOrEmpty(value)) return defaultValue; foreach (T item in Enum.GetValues(typeof(T))) { if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item; } return defaultValue; } I am getting a Error Constraint cannot be special class 'System.Enum' Fair enough, but is there a workaround to allow a Generic Enum, or am I going to have to mimic the Parse function and pass a type as an attribute, which forces the ugly boxing requirement to your code. EDIT All suggestions below have been greatly appreciated, thanks Have settled on (I've left the loop to maintain case insensitivity - I am usng this when parsing XML) public static class EnumUtils { public static T ParseEnum<T>(string value, T defaultValue) where T : struct, IConvertible { if (!typeof(T).IsEnum) throw new ArgumentException("T must be an enumerated type"); if (string.IsNullOrEmpty(value)) return defaultValue; foreach (T item in Enum.GetValues(typeof(T))) { if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item; } return defaultValue; } }

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• mocking collection behavior with Moq

  - by Stephen Patten

  Hello, I've read through some of the discussions on the Moq user group and have failed to find an example and have been so far unable to find the scenario that I have. Here is my question and code: // 6 periods var schedule = new List<PaymentPlanPeriod>() { new PaymentPlanPeriod(1000m, args.MinDate.ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(1).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(2).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(3).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(4).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(5).ToString()) }; // Now the proxy is correct with the schedule helper.Setup(h => h.GetPlanPeriods(It.IsAny<String>(), schedule)); Then in my tests I use Periods but the Mocked _PaymentPlanHelper never populates the collection, see below for usage: public IEnumerable<PaymentPlanPeriod> Periods { get { if (CanCalculateExpression()) _PaymentPlanHelper.GetPlanPeriods(this.ToString(), _PaymentSchedule); return _PaymentSchedule; } } Now if I change the mocked object to use another overloaded method of GetPlanPeriods that returns a List like so : var schedule = new List<PaymentPlanPeriod>() { new PaymentPlanPeriod(1000m, args.MinDate.ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(1).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(2).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(3).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(4).ToString()), new PaymentPlanPeriod(1000m, args.MinDate.Value.AddMonths(5).ToString()) }; helper.Setup(h => h.GetPlanPeriods(It.IsAny<String>())).Returns(new List<PaymentPlanPeriod>(schedule)); List<PaymentPlanPeriod> result = new _PaymentPlanHelper.GetPlanPeriods(this.ToString()); This works as expected. Any pointers would be awesome, as long as you don't bash my architecture... :) Thank you, Stephen

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• How to access a method on a generic datacontext which is only created at runtime

  - by Jeremy Holt

  I'm creating my generic DataContext using only the connectionString in the ctor. I have no issues in retrieving the table using DataContext.GetTable(). However, I need to also be able to retrieve entities of inline table functions. The dbml designer generates public IQueryable<testFunctionResult> testFunction() { return this.CreateMethodCallQuery<testFunctionResult>(this, ((MethodInfo)(MethodInfo.GetCurrentMethod()))); } The question is how do I get the MethodInfo.GetCurrentMethod() when the DataContext has no method called "testFunction", i.e.typeof(DataContext).GetMethod("testFunction") returns null? What I'm trying to achieve is something like: public class UnitofWork<T> { public UnitofWork(string connectionString) { this.DataContext = new DataContext(connectionString); } public UnitofWork(IQueryable<T> tableEntity) { _tableEntity = tableEntity; } public IQueryable<T> TableEntity { get { if (DataContext == null) return _tableEntity; var metaType = DataContext.Mapping.GetMetaType(typeof (T)); if (metaType.IsEntity) _tableEntity = DataContext.GetTable<T>(); else { var s = typeof(T).Name; string methodName = s.Substring(0, s.IndexOf("Result")) + "()"; // the designer automatically affixes "Result" to the type name // Make a method from methodName // _tableEntity = DataContext.CreateMethodCallQuery(DataContext, method, new object[]{}); } return _tableEntity; } set { _tableEntity = value; } } ) Thanks in advance for any insight Jeremy

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• Can memory be cleaned up?

  - by Tom

  I am working in Delphi 5 (with FastMM installed) on a Win32 project, and have recently been trying to drastically reduce the memory usage in this application. So far, I have cut the usage nearly in half, but noticed something when working on a separate task. When I minimized the application, the memory usage shrunk from 45 megs down to 1 meg, which I attributed to it paging out to disk. When I restored it and restarted working, the memory went up only to 15 megs. As I continued working, the memory usage slowly went up again, and a minimize and restore flushed it back down to 15 megs. So to my thinking, when my code tells the system to release the memory, it is still being held on to according to Windows, and the actual garbage collection doesn't kick in until a lot later. Can anyone confirm/deny this sort of behavior? Is it possible to get the memory cleaned up programatically? If I keep using the program without doing this manual flush, I get an out of memory error after a while, and would like to eliminate that. Thanks.

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• Grouping Collection seperating numeric 5 from String "5"

  - by invertedSpear

  BackGround: I have an advanced data grid. The data provider for this ADG is an ArrayCollection. There is a grouping collection on an ID field of this AC. Example of a couple items within this AC the AC var name is "arcTemplates": (mx.collections::ArrayCollection)#0 filterFunction = (null) length = 69 list = (mx.collections::ArrayList)#1 length = 69 source = (Array)#2 [0] (Object)#3 abbreviation = "sore-throat" insertDate = "11/16/2009" name = "sore throat" templateID = 234 templateType = "New Problem" templateTypeID = 1 [32] (Object)#35 abbreviation = 123 insertDate = "03/08/2010" name = 123 templateID = 297 templateType = "New Problem" templateTypeID = 1 [55] (Object)#58 abbreviation = 1234 insertDate = "11/16/2009" name = 1234 templateID = 227 templateType = "Exam" templateTypeID = 5 [56] (Object)#59 abbreviation = "breast only" insertDate = "03/15/2005" name = "breast exam" templateID = 195 templateType = "Exam" templateTypeID = 5 Example of Flex code leading to the Grouping: <mx:AdvancedDataGrid displayItemsExpanded="true" id="gridTemplates"> <mx:dataProvider> <mx:GroupingCollection id="gc" source="{arcTemplates}"> <mx:Grouping > <mx:GroupingField name="templateTypeID" compareFunction="gcSort"> GC sort function: public function gcSort(a:Object, b:Object):int{ return ObjectUtil.stringCompare(String(a.templateTypeID + a.name).toLowerCase(), String(b.templateTypeID + b.name).toLowerCase()); } Problem: In my AC example there are a few items, items 0, 32 and 56 properly sort and group to their templateTypeID, but item 55 does something weird. It seems to sort/group on the numeric 5 instead of the string "5". Gets stranger. If I change the name property to contain text (so 1234x) it then correctly sorts/groups to the string "5" Question: What is going on here and how do I fix it?

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