Articolo
11/18/2011

Thread Constructor (ParameterizedThreadStart)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Initializes a new instance of the Thread class, specifying a delegate that allows an object to be passed to the thread when the thread is started.

Namespace: System.Threading
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<SecuritySafeCriticalAttribute> _
Public Sub New ( _
    start As ParameterizedThreadStart _
)

[SecuritySafeCriticalAttribute]
public Thread(
    ParameterizedThreadStart start
)

Parameters

start
Type: System.Threading.ParameterizedThreadStart
A delegate that represents the methods to be invoked when this thread begins executing.

Exceptions

Exception	Condition
ArgumentNullException	start is nulla null reference (Nothing in Visual Basic).

Remarks

A thread does not begin executing when it is created. To schedule the thread for execution, call the Start method. To pass a data object to the thread, use the Start(Object) method overload.

Note:
Visual Basic and C# users can omit the ThreadStart or ParameterizedThreadStart constructor when creating a thread. The compilers automatically call the appropriate constructor. For Visual Basic, use the AddressOf operator when passing your method; for example, Dim t As New Thread(AddressOf ThreadProc).

Examples

The following example shows how to create and start a thread by using a ParameterizedThreadStart delegate with a static method.

The example displays its output in a TextBlock on the user interface (UI) thread. To access the TextBlock from the callback thread, the example uses the Dispatcher property to obtain a Dispatcher object for the TextBlock, and then uses 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. For example code that uses this constructor and passes thread synchronization objects to thread procedures, see EventWaitHandle.

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

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 
      ' ParameterizedThreadStart delegate. Visual Basic expands the 
      ' AddressOf expression to the appropriate delegate creation 
      ' syntax:
      '    New ParameterizedThreadStart(AddressOf Example.DoWork)
      '
      Dim newThread As New Thread(AddressOf Example.DoWork)
      newThread.Start(42)

   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(ByVal state As Object)

      Dim data As Integer = CInt(state)
      Dim display As New Action(Of String)(AddressOf DisplayOutput)

      outputBlock.Dispatcher.BeginInvoke(display, _
         String.Format("Shared thread procedure. Data={0}" & vbLf, data))

   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:
'
'Shared thread procedure. Data='42'

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 shared thread procedure, use
      // the class name and method name when you create the 
      // ParameterizedThreadStart delegate. C# infers the 
      // appropriate delegate creation syntax:
      //    New ParameterizedThreadStart(Example.DoWork)
      //
      Thread newThread = new Thread(Example.DoWork);
      newThread.Start(42);
   }

   // 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(object state)
   {
      int data = (int) state;

      outputBlock.Dispatcher.BeginInvoke(delegate () { 
         outputBlock.Text += String.Format("Static thread procedure. Data={0}\n", data); 
      });
   }
}

/* This code example produces the following output:

Static 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.

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