nullreferenceexception

问题 This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. Closed 6 years ago . I am getting NullReferenceException at the _dicCache.TryGetValue(objID, out newObject); line. And I have no Idea why this is happening at all. Can

问题 When launching my WinForms project (project only contains one source file, Program.cs), the debugger breaks with no stack trace on the following exception: System.ArgumentNullException was unhandled Message="Value cannot be null.\r\nParameter name: activationContext" Source="mscorlib" ParamName="activationContext" StackTrace: at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData) at System.Runtime.Hosting

问题 I'm getting some unexpected behaviour with a JoinAlias QueryOver in NHibernate. My entity essentially looks like this: public class Field { public virtual long Id { get; protected set; } public virtual Field Parent { get; protected set; } public virtual FieldType Type { get; protected set; } public virtual string Value { get; protected set; } ...(Ctors etc } My mapping is such: public class FieldMap : ClassMap<Field> { public FieldMap() { Id(x => x.Id) .GeneratedBy.Native(); References(x => x

问题 I recently made the statement to a colleague that: NullReferenceExceptions should never be explicitly caught I used the word never.... hmmm. I've never seen a appropriate use case myself for catching them but I wanted to check if anyone else has? Never is such a strong word after all..... 回答1: It depends on why; see Eric Lippert's blog entry. If they are "boneheaded exceptions", then no - just fix the calling code. In the rare case that they are "vexing exceptions" (i.e. the code you are

问题 .method public static void Test<class T>(object A_0) cil managed { // Code size 13 (0xd) .maxstack 1 .locals init (!!T V_0) IL_0000: ldarg.0 IL_0001: isinst !!T IL_0006: unbox.any !!T IL_000b: stloc.0 IL_000c: ret } // end of method DemoType::Test The equal C# code is: public static void Test<T>(object o) where T : class { T t = o as T; } My questions are: Why unbox.any been called? if you just do var a = father as child isinst intruction will call and no unbox.any, and If i'll remove the

问题 This question already has answers here : What is a NullReferenceException, and how do I fix it? (29 answers) Closed 5 years ago . I have the following code snippet that produces a compilation error: public List<string> batchaddresses; public MapFiles(string [] addresses) { for (int i = 0; i < addresses.Count(); i++) { batchaddresses.AddRange(Directory.GetFiles(addresses[i], "*.esy")); } } I get an error when I try to use the List<T>.AddRange() method: Object reference not set to an instance

问题 In a wpf standalone application (.exe) I have included a MediaElement in the MainWindow <Window x:Class="Media.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Main Window" Height="350" Width="525"> <Grid> <MediaElement x:Name="Player" Stretch="Uniform" LoadedBehavior="Manual" UnloadedBehavior="Stop"/> </Grid> </Window> and from the code behind I set its Source to any https Uri: public partial class

问题 Is there a way to do a generic cascading null reference check in c#? What i am trying to achieve is if i am trying to access a string variable which is part of a class C, which is inturn in class B, which is in A. A.B.C.str And that i am passed in A, i will have to check to see if A is null, then check if B is null, then check is C is null and then access str. Is it possible to have some method where - we can potentially pass in, A and A.B.C.str and it return null is anything was null or

问题 I have 2 Forms (Form1 and Form2) and a class (Class1). Form1 contains a button (Button1) and Form2 contains a RichTextBox (textBox1) When I press Button1 on Form1, I want the method (DoSomethingWithText) to be called. I keep getting "NullReferenceException - Object reference not set to an instance of an object". Here is a code example: Form1: namespace Test1 { public partial class Form1 : Form { Form2 frm2; Class1 cl; public Form1() { InitializeComponent(); } private void button1_Click(object

问题 For some reason, when certain bots visit the site, generating a url with the UrlHelper.Action method raises a null exception from System.Web.HttpServerVarsCollection.Get . I've done some debugging and the call stack originiates with an attempt to get the 'HTTP_X_ORIGINAL_URL' from the HttpContextBase.Request.ServerVariables collection. If I visit the same address directly from a browser - no problem. The page is server and no error is logged. It only seems to occur when visited by a bot. Not