Best Way to Invoke Any Cross-Threaded Code?

问题:

I know that this question has been asked before, but I'm looking for a way to:

1. streamline the creation of safe cross-threaded code.
2. reuse this code in any situation (no Windows Forms references).

Here's what I have so far, but I want to remove the Windows Forms references. Any ideas?

public delegate void SafeInvokeDelegate(System.Action action); public class SafeInvoke {     private readonly System.Windows.Forms.Control _threadControl;      public SafeInvoke()     {         _threadControl = new System.Windows.Forms.Control();     }      public void Invoke(System.Action action)     {         if (_threadControl.InvokeRequired)             _threadControl.Invoke(new SafeInvokeDelegate(Invoke), new object[] {action});         else if (action != null) action();     } } 

The above class might be used this way:

SafeInvoke _safeInvoker = new SafeInvoke(); void SafeClearItems() {     _safeInvoker.Invoke(delegate         {             listView1.Items.Clear();         }); } 

How would I remove the System.Windows.Forms.Control in the SafeInvoke class but keep the same functionality?

回答1:

You also could use an extension method and lambdas to make your code much cleaner.

using System.ComponentModel; public static class ISynchronizeInvokeExtensions {   public static void InvokeEx(this T @this, Action action) where T : ISynchronizeInvoke   {     if (@this.InvokeRequired)     {       @this.Invoke(action, new object[] { @this });     }     else     {       action(@this);     }   } } 

So now you can use InvokeEx on any ISynchronizeInvoke and be able to access the properties and fields of implementing class.

this.InvokeEx(f => f.listView1.Items.Clear()); 

回答2:

Use ISynchronizeInvoke instead of Control. That's the interface that Control implements with Invoke/BeginInvoke/EndInvoke/InvokeRequired.

An alternative is to use SynchronizationContext.Current - which is what BackgroundWorker uses, I believe.

回答3:

Here it is in VB.net, very similar to Samuel's answer. I have four overloads depending on whether you want a subroutine or function and whether or not there's a parameter. It would be easy to add more overloads for more parameters. VB.Net is able to infer the types.

Module ISynchronizeInvokeExtensions     Public Delegate Function GenericLambdaFunctionWithParam(Of InputType, OutputType)(ByVal input As InputType) As OutputType     Private Delegate Function InvokeLambdaFunctionCallback(Of InputType, OutputType)(ByVal f As GenericLambdaFunctionWithParam(Of InputType, OutputType), ByVal input As InputType, ByVal c As System.ComponentModel.ISynchronizeInvoke) As OutputType     Public Function InvokeEx(Of InputType, OutputType)(ByVal f As GenericLambdaFunctionWithParam(Of InputType, OutputType), ByVal input As InputType, ByVal c As System.ComponentModel.ISynchronizeInvoke) As OutputType         If c.InvokeRequired Then             Dim d As New InvokeLambdaFunctionCallback(Of InputType, OutputType)(AddressOf InvokeEx)             Return DirectCast(c.Invoke(d, New Object() {f, input, c}), OutputType)         Else             Return f(input)         End If     End Function      Public Delegate Sub GenericLambdaSubWithParam(Of InputType)(ByVal input As InputType)     Public Sub InvokeEx(Of InputType)(ByVal s As GenericLambdaSubWithParam(Of InputType), ByVal input As InputType, ByVal c As System.ComponentModel.ISynchronizeInvoke)         InvokeEx(Of InputType, Object)(Function(i As InputType) As Object                                            s(i)                                            Return Nothing                                        End Function, input, c)     End Sub      Public Delegate Sub GenericLambdaSub()     Public Sub InvokeEx(ByVal s As GenericLambdaSub, ByVal c As System.ComponentModel.ISynchronizeInvoke)         InvokeEx(Of Object, Object)(Function(i As Object) As Object                                         s()                                         Return Nothing                                     End Function, Nothing, c)     End Sub      Public Delegate Function GenericLambdaFunction(Of OutputType)() As OutputType     Public Function InvokeEx(Of OutputType)(ByVal f As GenericLambdaFunction(Of OutputType), ByVal c As System.ComponentModel.ISynchronizeInvoke) As OutputType         Return InvokeEx(Of Object, OutputType)(Function(i As Object) f(), Nothing, c)     End Function End Module 

Usage (run this in a backgroundworker):

    InvokeEx(Sub(x As String) Me.Text = x, "foo", Me) 'set form title to foo     InvokeEx(AddressOf MsgBox, Me.Text, Me)     InvokeEx(Sub() Me.Text &= "!", "foo", Me) 'append "!" to form title     InvokeEx(AddressOf MsgBox, Me.Text, Me)     Dim s As String = InvokeEx(Function() Me.Text, Me) & "bar" 'get form title to backgorundworker thread     InvokeEx(AddressOf MsgBox, s, Me) 'display the string from backgroundworker thread 

回答4:

here's the VB equivalent code to Samuel's answer that i use. notice i actually have 2 extensions functions, but i must admit i don't know why they are there. i copied my C# version years ago (maybe from this site) and it had both extension functions, but for what reason, i don't fully understand. i just copied it and how to use it, and i half understand all that goes on 'under the hood' with these complicated functions.

#Const System_ComponentModel = True #Const System_Drawing = False  Option Compare Binary Option Explicit On Option Strict On  Imports System.Collections Imports System.Runtime.CompilerServices ' for Extension() attribute Imports System.Text #If System_ComponentModel Then Imports System.ComponentModel #End If #If System_Drawing Then Imports System.Drawing #End If  Public Module MyExtensions      ' other #Region blocks are removed. i use many in my Extensions     ' module/class. the below code is only the 2 relevant extension     ' for this 'SafeInvoke' functionality. but i use other regions     ' such as "String extensions" and "Numeric extensions". i use     ' the above System_ComponentModel and System_Drawing compiler     ' directives to include or exclude blocks of code that i want     ' to either include or exclude in a project, which allows me to     ' easily compare my code in one project with the same file in     ' other projects to syncronise new changes across projects.     ' you can scrap pretty much all the code above,     ' but i'm giving it here so you see it in the full context.      #Region "ISynchronizeInvoke extensions"      #If System_ComponentModel Then                   Public Function SafeInvoke(Of T As ISynchronizeInvoke, TResult)(isi As T, callFunction As Func(Of T, TResult)) As TResult             If (isi.InvokeRequired) Then                 Dim result As IAsyncResult = isi.BeginInvoke(callFunction, New Object() {isi})                 Dim endresult As Object = isi.EndInvoke(result)                 Return DirectCast(endresult, TResult)             Else                 Return callFunction(isi)             End If         End Function          ''' 
         ''' This can be used in VB with:         ''' txtMyTextBox.SafeInvoke(Sub(d) d.Text = "This is my new Text value.")         ''' or:         ''' txtMyTextBox.SafeInvoke(Sub(d) d.Text = myTextStringVariable)         ''' 
         '''          '''          '''          '''          Public Sub SafeInvoke(Of T As ISynchronizeInvoke)(isi As T, callFunction As Action(Of T))             If isi.InvokeRequired Then                 isi.BeginInvoke(callFunction, New Object() {isi})             Else                 callFunction(isi)             End If         End Sub      #End If      #End Region      ' other #Region blocks are removed from here too.  End Module 

And the C# version is:

#define System_ComponentModel #undef  System_Drawing  using System; using System.Collections.Generic; using System.Linq; using System.Text;  #if System_ComponentModel using System.ComponentModel; #endif #if System_Drawing using System.Drawing; #endif  namespace MyCompany.Extensions {     static partial class MyExtensions     {          // other #Region blocks are removed. i use many in my Extensions         // module/class. the below code is only the 2 relevant extension         // for this 'SafeInvoke' functionality. but i use other regions         // such as "String extensions" and "Numeric extensions". i use         // the above System_ComponentModel and System_Drawing compiler         // directives to include or exclude blocks of code that i want         // to either include or exclude in a project, which allows me to         // easily compare my code in one project with the same file in         // other projects to syncronise new changes across projects.         // you can scrap pretty much all the code above,         // but i'm giving it here so you see it in the full context.          #region ISynchronizeInvoke extensions #if System_ComponentModel          public static TResult SafeInvoke(this T isi, Func callFunction) where T : ISynchronizeInvoke         {             if (isi.InvokeRequired)             {                 IAsyncResult result = isi.BeginInvoke(callFunction, new object[] { isi });                 object endResult = isi.EndInvoke(result); return (TResult)endResult;             }             else                 return callFunction(isi);         }          /// 
         /// This can be used in C# with:         /// txtMyTextBox.SafeInvoke(d => d.Text = "This is my new Text value.");         /// or:         /// txtMyTextBox.SafeInvoke(d => d.Text = myTextStringVariable);         /// 
         ///          ///          ///          public static void SafeInvoke(this T isi, Action callFunction) where T : ISynchronizeInvoke         {             if (isi.InvokeRequired) isi.BeginInvoke(callFunction, new object[] { isi });             else                 callFunction(isi);         }  #endif         #endregion          // other #Region blocks are removed from here too.      } // static class MyExtensions  } // namespace 

Happy coding!

回答5:

Now a days it's Easy to Invoke e.g say we want to invoke a Label(lblVal) to get value of txtVal

lblVal.invoke((MethodInvoker)delegate{txtVal.Text = lblVal.Text;}); 

as easy as that :D

文章来源: Best Way to Invoke Any Cross-Threaded Code?