ThreadStart Delegate
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Represents the method that executes on a Thread.
Namespace: System.Threading
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
<ComVisibleAttribute(True)> _
Public Delegate Sub ThreadStart
[ComVisibleAttribute(true)]
public delegate void ThreadStart()
Remarks
When a managed thread is created, the method that executes on the thread is represented by a ThreadStart delegate or a ParameterizedThreadStart delegate that is passed to the Thread constructor. The thread does not begin executing until the Thread.Start method is called. Execution begins at the first line of the method that is represented by the ThreadStart or ParameterizedThreadStart delegate.
.gif "Note") Note: |
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Visual Basic and C# users can omit the ThreadStart or ParameterizedThreadStart delegate constructor when creating a thread. In Visual Basic, use the AddressOf operator when passing your method to the Thread constructor; for example, Dim t As New Thread(AddressOf ThreadProc). In C#, just specify the name of the thread procedure. The compiler selects the correct delegate constructor. |
Examples
This section contains two examples. The first example shows how to use a ThreadStart delegate to execute a static method, and the second shows how to use a ThreadStart delegate to execute an instance method.
The examples display their output in a TextBlock on the UI thread. To access the TextBlock from the callback thread, the examples use the Dispatcher property to obtain a Dispatcher object for the TextBlock, and then use the Dispatcher.BeginInvoke method to make the cross-thread call.
For more information about thread creation, see Creating Threads and Passing Data at Start Time.
Example 1
The following code example shows how to use a ThreadStart delegate to execute a static method.
Imports System.Threading
Public Class Example
Private Shared outputBlock As System.Windows.Controls.TextBlock
Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
Example.outputBlock = outputBlock
' To start a thread using a static thread procedure, use the
' class name and method name when you create the ThreadStart
' delegate. Visual Basic expands the AddressOf expression
' to the appropriate delegate creation syntax:
' New ThreadStart(AddressOf Example.DoWork)
'
Dim newThread As New Thread(AddressOf Example.DoWork)
newThread.Start()
End Sub
' Simulate work. To communicate with objects on the UI thread, get the
' Dispatcher for one of the UI objects. Use the Dispatcher object's
' BeginInvoke method to queue a delegate that will run on the UI thread,
' and therefore can safely access UI elements like the TextBlock.
Private Shared Sub DoWork()
Dim display As New Action(Of String)(AddressOf DisplayOutput)
outputBlock.Dispatcher.BeginInvoke(display, _
"Hello from a Shared thread procedure." & vbCrLf)
End Sub
' The Dispatcher.BeginInvoke method runs this helper method on the
' UI thread, so it can safely access the TextBlock that is used to
' display the output.
Private Shared Sub DisplayOutput(msg)
outputBlock.Text &= msg
End Sub
End Class
' This code example produces the following output:
'
'Hello from a Shared thread procedure.
using System;
using System.Threading;
public class Example
{
private static System.Windows.Controls.TextBlock outputBlock;
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
Example.outputBlock = outputBlock;
// To start a thread using a static thread procedure, use the
// class name and method name when you create the ThreadStart
// delegate. C# expands the method name to the appropriate
// delegate creation syntax:
// New ThreadStart(Example.DoWork)
//
Thread newThread = new Thread(Example.DoWork);
newThread.Start();
}
// Simulate work. To communicate with objects on the UI thread, get the
// Dispatcher for one of the UI objects. Use the Dispatcher object's
// BeginInvoke method to queue a delegate that will run on the UI thread,
// and therefore can safely access UI elements like the TextBlock.
private static void DoWork()
{
outputBlock.Dispatcher.BeginInvoke(delegate () {
outputBlock.Text += "Hello from a static thread procedure.\n";
});
}
}
/* This code example produces the following output:
Hello from a static thread procedure.
*/
Example 2
The following code example shows how to use a ThreadStart delegate to execute an instance method.
Imports System.Threading
Public Class Example
Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
' To start a thread using an instance method for the thread
' procedure, use the instance variable and method name when
' you create the ThreadStart delegate. Visual Basic expands
' the AddressOf expression to the appropriate delegate
' creation syntax:
' New ThreadStart(AddressOf w.DoMoreWork)
'
Dim w As New Work()
w.Data = 42
w.Output = outputBlock
Dim newThread As Thread = New Thread(AddressOf w.DoMoreWork)
newThread.Start()
End Sub
End Class
Public Class Work
Public Data As Integer
Public Output As System.Windows.Controls.TextBlock
' Simulate work. To communicate with objects on the UI thread, get the
' Dispatcher for one of the UI objects. Use the Dispatcher object's
' BeginInvoke method to queue a delegate that will run on the UI thread,
' and therefore can safely access UI elements like the TextBlock.
Public Sub DoMoreWork()
Dim display As New Action(Of String)(AddressOf DisplayOutput)
Output.Dispatcher.BeginInvoke(display, _
String.Format("Instance thread procedure. Data={0}", Data) & vbCrLf)
End Sub
' The Dispatcher.BeginInvoke method runs this helper method on the
' UI thread, so it can safely access the TextBlock that is used to
' display the output.
Private Sub DisplayOutput(msg)
Output.Text &= msg
End Sub
End Class
' This code example produces the following output:
'
'Instance thread procedure. Data=42
using System;
using System.Threading;
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
// To start a thread using an instance method for the thread
// procedure, use the instance variable and method name when
// you create the ThreadStart delegate. C# expands the object
// reference and method name to the appropriate delegate
// creation syntax:
// New ThreadStart(AddressOf w.DoMoreWork)
//
Work w = new Work();
w.Data = 42;
w.Output = outputBlock;
Thread newThread = new Thread(w.DoMoreWork);
newThread.Start();
}
}
public class Work
{
public int Data;
public System.Windows.Controls.TextBlock Output;
// Simulate work. To communicate with objects on the UI thread, get the
// Dispatcher for one of the UI objects. Use the Dispatcher object's
// BeginInvoke method to queue a delegate that will run on the UI thread,
// and therefore can safely access UI elements like the TextBlock.
public void DoMoreWork()
{
Output.Dispatcher.BeginInvoke(delegate () {
Output.Text += String.Format("Instance thread procedure. Data={0}\n", Data);
});
}
}
// This code example produces the following output:
//
//Instance thread procedure. Data=42
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
See Also