How to: Implement a Form That Uses a Background Operation
The following example program creates a form that calculates Fibonacci numbers. The calculation runs on a thread that is separate from the user interface thread, so the user interface continues to run without delays as the calculation proceeds.
There is extensive support for this task in Visual Studio.
Walkthrough: Implementing a Form That Uses a Background Operation
Walkthrough: Implementing a Form That Uses a Background Operation
Walkthrough: Implementing a Form That Uses a Background Operation
Walkthrough: Implementing a Form That Uses a Background Operation
Example
Imports System
Imports System.Collections
Imports System.ComponentModel
Imports System.Drawing
Imports System.Threading
Imports System.Windows.Forms
Public Class FibonacciForm
Inherits System.Windows.Forms.Form
Private numberToCompute As Integer = 0
Private highestPercentageReached As Integer = 0
Private numericUpDown1 As System.Windows.Forms.NumericUpDown
Private WithEvents startAsyncButton As System.Windows.Forms.Button
Private WithEvents cancelAsyncButton As System.Windows.Forms.Button
Private progressBar1 As System.Windows.Forms.ProgressBar
Private resultLabel As System.Windows.Forms.Label
Private WithEvents backgroundWorker1 As System.ComponentModel.BackgroundWorker
Public Sub New()
InitializeComponent()
End Sub 'New
Private Sub startAsyncButton_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles startAsyncButton.Click
' Reset the text in the result label.
resultLabel.Text = [String].Empty
' Disable the UpDown control until
' the asynchronous operation is done.
Me.numericUpDown1.Enabled = False
' Disable the Start button until
' the asynchronous operation is done.
Me.startAsyncButton.Enabled = False
' Enable the Cancel button while
' the asynchronous operation runs.
Me.cancelAsyncButton.Enabled = True
' Get the value from the UpDown control.
numberToCompute = CInt(numericUpDown1.Value)
' Reset the variable for percentage tracking.
highestPercentageReached = 0
' Start the asynchronous operation.
backgroundWorker1.RunWorkerAsync(numberToCompute)
End Sub
Private Sub cancelAsyncButton_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles cancelAsyncButton.Click
' Cancel the asynchronous operation.
Me.backgroundWorker1.CancelAsync()
' Disable the Cancel button.
cancelAsyncButton.Enabled = False
End Sub 'cancelAsyncButton_Click
' This event handler is where the actual work is done.
Private Sub backgroundWorker1_DoWork( _
ByVal sender As Object, _
ByVal e As DoWorkEventArgs) _
Handles backgroundWorker1.DoWork
' Get the BackgroundWorker object that raised this event.
Dim worker As BackgroundWorker = _
CType(sender, BackgroundWorker)
' Assign the result of the computation
' to the Result property of the DoWorkEventArgs
' object. This is will be available to the
' RunWorkerCompleted eventhandler.
e.Result = ComputeFibonacci(e.Argument, worker, e)
End Sub 'backgroundWorker1_DoWork
' This event handler deals with the results of the
' background operation.
Private Sub backgroundWorker1_RunWorkerCompleted( _
ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs) _
Handles backgroundWorker1.RunWorkerCompleted
' First, handle the case where an exception was thrown.
If (e.Error IsNot Nothing) Then
MessageBox.Show(e.Error.Message)
ElseIf e.Cancelled Then
' Next, handle the case where the user canceled the
' operation.
' Note that due to a race condition in
' the DoWork event handler, the Cancelled
' flag may not have been set, even though
' CancelAsync was called.
resultLabel.Text = "Canceled"
Else
' Finally, handle the case where the operation succeeded.
resultLabel.Text = e.Result.ToString()
End If
' Enable the UpDown control.
Me.numericUpDown1.Enabled = True
' Enable the Start button.
startAsyncButton.Enabled = True
' Disable the Cancel button.
cancelAsyncButton.Enabled = False
End Sub 'backgroundWorker1_RunWorkerCompleted
' This event handler updates the progress bar.
Private Sub backgroundWorker1_ProgressChanged( _
ByVal sender As Object, ByVal e As ProgressChangedEventArgs) _
Handles backgroundWorker1.ProgressChanged
Me.progressBar1.Value = e.ProgressPercentage
End Sub
' This is the method that does the actual work. For this
' example, it computes a Fibonacci number and
' reports progress as it does its work.
Function ComputeFibonacci( _
ByVal n As Integer, _
ByVal worker As BackgroundWorker, _
ByVal e As DoWorkEventArgs) As Long
' The parameter n must be >= 0 and <= 91.
' Fib(n), with n > 91, overflows a long.
If n < 0 OrElse n > 91 Then
Throw New ArgumentException( _
"value must be >= 0 and <= 91", "n")
End If
Dim result As Long = 0
' Abort the operation if the user has canceled.
' Note that a call to CancelAsync may have set
' CancellationPending to true just after the
' last invocation of this method exits, so this
' code will not have the opportunity to set the
' DoWorkEventArgs.Cancel flag to true. This means
' that RunWorkerCompletedEventArgs.Cancelled will
' not be set to true in your RunWorkerCompleted
' event handler. This is a race condition.
If worker.CancellationPending Then
e.Cancel = True
Else
If n < 2 Then
result = 1
Else
result = ComputeFibonacci(n - 1, worker, e) + _
ComputeFibonacci(n - 2, worker, e)
End If
' Report progress as a percentage of the total task.
Dim percentComplete As Integer = _
CSng(n) / CSng(numberToCompute) * 100
If percentComplete > highestPercentageReached Then
highestPercentageReached = percentComplete
worker.ReportProgress(percentComplete)
End If
End If
Return result
End Function
Private Sub InitializeComponent()
Me.numericUpDown1 = New System.Windows.Forms.NumericUpDown
Me.startAsyncButton = New System.Windows.Forms.Button
Me.cancelAsyncButton = New System.Windows.Forms.Button
Me.resultLabel = New System.Windows.Forms.Label
Me.progressBar1 = New System.Windows.Forms.ProgressBar
Me.backgroundWorker1 = New System.ComponentModel.BackgroundWorker
CType(Me.numericUpDown1, System.ComponentModel.ISupportInitialize).BeginInit()
Me.SuspendLayout()
'
'numericUpDown1
'
Me.numericUpDown1.Location = New System.Drawing.Point(16, 16)
Me.numericUpDown1.Maximum = New Decimal(New Integer() {91, 0, 0, 0})
Me.numericUpDown1.Minimum = New Decimal(New Integer() {1, 0, 0, 0})
Me.numericUpDown1.Name = "numericUpDown1"
Me.numericUpDown1.Size = New System.Drawing.Size(80, 20)
Me.numericUpDown1.TabIndex = 0
Me.numericUpDown1.Value = New Decimal(New Integer() {1, 0, 0, 0})
'
'startAsyncButton
'
Me.startAsyncButton.Location = New System.Drawing.Point(16, 72)
Me.startAsyncButton.Name = "startAsyncButton"
Me.startAsyncButton.Size = New System.Drawing.Size(120, 23)
Me.startAsyncButton.TabIndex = 1
Me.startAsyncButton.Text = "Start Async"
'
'cancelAsyncButton
'
Me.cancelAsyncButton.Enabled = False
Me.cancelAsyncButton.Location = New System.Drawing.Point(153, 72)
Me.cancelAsyncButton.Name = "cancelAsyncButton"
Me.cancelAsyncButton.Size = New System.Drawing.Size(119, 23)
Me.cancelAsyncButton.TabIndex = 2
Me.cancelAsyncButton.Text = "Cancel Async"
'
'resultLabel
'
Me.resultLabel.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D
Me.resultLabel.Location = New System.Drawing.Point(112, 16)
Me.resultLabel.Name = "resultLabel"
Me.resultLabel.Size = New System.Drawing.Size(160, 23)
Me.resultLabel.TabIndex = 3
Me.resultLabel.Text = "(no result)"
Me.resultLabel.TextAlign = System.Drawing.ContentAlignment.MiddleCenter
'
'progressBar1
'
Me.progressBar1.Location = New System.Drawing.Point(18, 48)
Me.progressBar1.Name = "progressBar1"
Me.progressBar1.Size = New System.Drawing.Size(256, 8)
Me.progressBar1.TabIndex = 4
'
'backgroundWorker1
'
Me.backgroundWorker1.WorkerReportsProgress = True
Me.backgroundWorker1.WorkerSupportsCancellation = True
'
'FibonacciForm
'
Me.ClientSize = New System.Drawing.Size(292, 118)
Me.Controls.Add(Me.progressBar1)
Me.Controls.Add(Me.resultLabel)
Me.Controls.Add(Me.cancelAsyncButton)
Me.Controls.Add(Me.startAsyncButton)
Me.Controls.Add(Me.numericUpDown1)
Me.Name = "FibonacciForm"
Me.Text = "Fibonacci Calculator"
CType(Me.numericUpDown1, System.ComponentModel.ISupportInitialize).EndInit()
Me.ResumeLayout(False)
End Sub 'InitializeComponent
<STAThread()> _
Shared Sub Main()
Application.Run(New FibonacciForm)
End Sub 'Main
End Class 'FibonacciForm
using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Threading;
using System.Windows.Forms;
namespace BackgroundWorkerExample
{
public class FibonacciForm : System.Windows.Forms.Form
{
private int numberToCompute = 0;
private int highestPercentageReached = 0;
private System.Windows.Forms.NumericUpDown numericUpDown1;
private System.Windows.Forms.Button startAsyncButton;
private System.Windows.Forms.Button cancelAsyncButton;
private System.Windows.Forms.ProgressBar progressBar1;
private System.Windows.Forms.Label resultLabel;
private System.ComponentModel.BackgroundWorker backgroundWorker1;
public FibonacciForm()
{
InitializeComponent();
InitializeBackgoundWorker();
}
// Set up the BackgroundWorker object by
// attaching event handlers.
private void InitializeBackgoundWorker()
{
backgroundWorker1.DoWork +=
new DoWorkEventHandler(backgroundWorker1_DoWork);
backgroundWorker1.RunWorkerCompleted +=
new RunWorkerCompletedEventHandler(
backgroundWorker1_RunWorkerCompleted);
backgroundWorker1.ProgressChanged +=
new ProgressChangedEventHandler(
backgroundWorker1_ProgressChanged);
}
private void startAsyncButton_Click(System.Object sender,
System.EventArgs e)
{
// Reset the text in the result label.
resultLabel.Text = String.Empty;
// Disable the UpDown control until
// the asynchronous operation is done.
this.numericUpDown1.Enabled = false;
// Disable the Start button until
// the asynchronous operation is done.
this.startAsyncButton.Enabled = false;
// Enable the Cancel button while
// the asynchronous operation runs.
this.cancelAsyncButton.Enabled = true;
// Get the value from the UpDown control.
numberToCompute = (int)numericUpDown1.Value;
// Reset the variable for percentage tracking.
highestPercentageReached = 0;
// Start the asynchronous operation.
backgroundWorker1.RunWorkerAsync(numberToCompute);
}
private void cancelAsyncButton_Click(System.Object sender,
System.EventArgs e)
{
// Cancel the asynchronous operation.
this.backgroundWorker1.CancelAsync();
// Disable the Cancel button.
cancelAsyncButton.Enabled = false;
}
// This event handler is where the actual,
// potentially time-consuming work is done.
private void backgroundWorker1_DoWork(object sender,
DoWorkEventArgs e)
{
// Get the BackgroundWorker that raised this event.
BackgroundWorker worker = sender as BackgroundWorker;
// Assign the result of the computation
// to the Result property of the DoWorkEventArgs
// object. This is will be available to the
// RunWorkerCompleted eventhandler.
e.Result = ComputeFibonacci((int)e.Argument, worker, e);
}
// This event handler deals with the results of the
// background operation.
private void backgroundWorker1_RunWorkerCompleted(
object sender, RunWorkerCompletedEventArgs e)
{
// First, handle the case where an exception was thrown.
if (e.Error != null)
{
MessageBox.Show(e.Error.Message);
}
else if (e.Cancelled)
{
// Next, handle the case where the user canceled
// the operation.
// Note that due to a race condition in
// the DoWork event handler, the Cancelled
// flag may not have been set, even though
// CancelAsync was called.
resultLabel.Text = "Canceled";
}
else
{
// Finally, handle the case where the operation
// succeeded.
resultLabel.Text = e.Result.ToString();
}
// Enable the UpDown control.
this.numericUpDown1.Enabled = true;
// Enable the Start button.
startAsyncButton.Enabled = true;
// Disable the Cancel button.
cancelAsyncButton.Enabled = false;
}
// This event handler updates the progress bar.
private void backgroundWorker1_ProgressChanged(object sender,
ProgressChangedEventArgs e)
{
this.progressBar1.Value = e.ProgressPercentage;
}
// This is the method that does the actual work. For this
// example, it computes a Fibonacci number and
// reports progress as it does its work.
long ComputeFibonacci(int n, BackgroundWorker worker, DoWorkEventArgs e)
{
// The parameter n must be >= 0 and <= 91.
// Fib(n), with n > 91, overflows a long.
if ((n < 0) || (n > 91))
{
throw new ArgumentException(
"value must be >= 0 and <= 91", "n");
}
long result = 0;
// Abort the operation if the user has canceled.
// Note that a call to CancelAsync may have set
// CancellationPending to true just after the
// last invocation of this method exits, so this
// code will not have the opportunity to set the
// DoWorkEventArgs.Cancel flag to true. This means
// that RunWorkerCompletedEventArgs.Cancelled will
// not be set to true in your RunWorkerCompleted
// event handler. This is a race condition.
if (worker.CancellationPending)
{
e.Cancel = true;
}
else
{
if (n < 2)
{
result = 1;
}
else
{
result = ComputeFibonacci(n - 1, worker, e) +
ComputeFibonacci(n - 2, worker, e);
}
// Report progress as a percentage of the total task.
int percentComplete =
(int)((float)n / (float)numberToCompute * 100);
if (percentComplete > highestPercentageReached)
{
highestPercentageReached = percentComplete;
worker.ReportProgress(percentComplete);
}
}
return result;
}
#region Windows Form Designer generated code
private void InitializeComponent()
{
this.numericUpDown1 = new System.Windows.Forms.NumericUpDown();
this.startAsyncButton = new System.Windows.Forms.Button();
this.cancelAsyncButton = new System.Windows.Forms.Button();
this.resultLabel = new System.Windows.Forms.Label();
this.progressBar1 = new System.Windows.Forms.ProgressBar();
this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker();
((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).BeginInit();
this.SuspendLayout();
//
// numericUpDown1
//
this.numericUpDown1.Location = new System.Drawing.Point(16, 16);
this.numericUpDown1.Maximum = new System.Decimal(new int[] {
91,
0,
0,
0});
this.numericUpDown1.Minimum = new System.Decimal(new int[] {
1,
0,
0,
0});
this.numericUpDown1.Name = "numericUpDown1";
this.numericUpDown1.Size = new System.Drawing.Size(80, 20);
this.numericUpDown1.TabIndex = 0;
this.numericUpDown1.Value = new System.Decimal(new int[] {
1,
0,
0,
0});
//
// startAsyncButton
//
this.startAsyncButton.Location = new System.Drawing.Point(16, 72);
this.startAsyncButton.Name = "startAsyncButton";
this.startAsyncButton.Size = new System.Drawing.Size(120, 23);
this.startAsyncButton.TabIndex = 1;
this.startAsyncButton.Text = "Start Async";
this.startAsyncButton.Click += new System.EventHandler(this.startAsyncButton_Click);
//
// cancelAsyncButton
//
this.cancelAsyncButton.Enabled = false;
this.cancelAsyncButton.Location = new System.Drawing.Point(153, 72);
this.cancelAsyncButton.Name = "cancelAsyncButton";
this.cancelAsyncButton.Size = new System.Drawing.Size(119, 23);
this.cancelAsyncButton.TabIndex = 2;
this.cancelAsyncButton.Text = "Cancel Async";
this.cancelAsyncButton.Click += new System.EventHandler(this.cancelAsyncButton_Click);
//
// resultLabel
//
this.resultLabel.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.resultLabel.Location = new System.Drawing.Point(112, 16);
this.resultLabel.Name = "resultLabel";
this.resultLabel.Size = new System.Drawing.Size(160, 23);
this.resultLabel.TabIndex = 3;
this.resultLabel.Text = "(no result)";
this.resultLabel.TextAlign = System.Drawing.ContentAlignment.MiddleCenter;
//
// progressBar1
//
this.progressBar1.Location = new System.Drawing.Point(18, 48);
this.progressBar1.Name = "progressBar1";
this.progressBar1.Size = new System.Drawing.Size(256, 8);
this.progressBar1.Step = 2;
this.progressBar1.TabIndex = 4;
//
// backgroundWorker1
//
this.backgroundWorker1.WorkerReportsProgress = true;
this.backgroundWorker1.WorkerSupportsCancellation = true;
//
// FibonacciForm
//
this.ClientSize = new System.Drawing.Size(292, 118);
this.Controls.Add(this.progressBar1);
this.Controls.Add(this.resultLabel);
this.Controls.Add(this.cancelAsyncButton);
this.Controls.Add(this.startAsyncButton);
this.Controls.Add(this.numericUpDown1);
this.Name = "FibonacciForm";
this.Text = "Fibonacci Calculator";
((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).EndInit();
this.ResumeLayout(false);
}
#endregion
[STAThread]
static void Main()
{
Application.Run(new FibonacciForm());
}
}
}
#using <System.Drawing.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>
using namespace System;
using namespace System::Collections;
using namespace System::ComponentModel;
using namespace System::Drawing;
using namespace System::Threading;
using namespace System::Windows::Forms;
public ref class FibonacciForm: public System::Windows::Forms::Form
{
private:
int numberToCompute;
int highestPercentageReached;
System::Windows::Forms::NumericUpDown^ numericUpDown1;
System::Windows::Forms::Button^ startAsyncButton;
System::Windows::Forms::Button^ cancelAsyncButton;
System::Windows::Forms::ProgressBar^ progressBar1;
System::Windows::Forms::Label ^ resultLabel;
System::ComponentModel::BackgroundWorker^ backgroundWorker1;
public:
FibonacciForm()
{
InitializeComponent();
numberToCompute = highestPercentageReached = 0;
InitializeBackgoundWorker();
}
private:
// Set up the BackgroundWorker object by
// attaching event handlers.
void InitializeBackgoundWorker()
{
backgroundWorker1->DoWork += gcnew DoWorkEventHandler( this, &FibonacciForm::backgroundWorker1_DoWork );
backgroundWorker1->RunWorkerCompleted += gcnew RunWorkerCompletedEventHandler( this, &FibonacciForm::backgroundWorker1_RunWorkerCompleted );
backgroundWorker1->ProgressChanged += gcnew ProgressChangedEventHandler( this, &FibonacciForm::backgroundWorker1_ProgressChanged );
}
void startAsyncButton_Click( System::Object^ /*sender*/, System::EventArgs^ /*e*/ )
{
// Reset the text in the result label.
resultLabel->Text = String::Empty;
// Disable the UpDown control until
// the asynchronous operation is done.
this->numericUpDown1->Enabled = false;
// Disable the Start button until
// the asynchronous operation is done.
this->startAsyncButton->Enabled = false;
// Enable the Cancel button while
// the asynchronous operation runs.
this->cancelAsyncButton->Enabled = true;
// Get the value from the UpDown control.
numberToCompute = (int)numericUpDown1->Value;
// Reset the variable for percentage tracking.
highestPercentageReached = 0;
// Start the asynchronous operation.
backgroundWorker1->RunWorkerAsync( numberToCompute );
}
void cancelAsyncButton_Click( System::Object^ /*sender*/, System::EventArgs^ /*e*/ )
{
// Cancel the asynchronous operation.
this->backgroundWorker1->CancelAsync();
// Disable the Cancel button.
cancelAsyncButton->Enabled = false;
}
// This event handler is where the actual,
// potentially time-consuming work is done.
void backgroundWorker1_DoWork( Object^ sender, DoWorkEventArgs^ e )
{
// Get the BackgroundWorker that raised this event.
BackgroundWorker^ worker = dynamic_cast<BackgroundWorker^>(sender);
// Assign the result of the computation
// to the Result property of the DoWorkEventArgs
// object. This is will be available to the
// RunWorkerCompleted eventhandler.
e->Result = ComputeFibonacci( safe_cast<Int32>(e->Argument), worker, e );
}
// This event handler deals with the results of the
// background operation.
void backgroundWorker1_RunWorkerCompleted( Object^ /*sender*/, RunWorkerCompletedEventArgs^ e )
{
// First, handle the case where an exception was thrown.
if ( e->Error != nullptr )
{
MessageBox::Show( e->Error->Message );
}
else
if ( e->Cancelled )
{
// Next, handle the case where the user cancelled
// the operation.
// Note that due to a race condition in
// the DoWork event handler, the Cancelled
// flag may not have been set, even though
// CancelAsync was called.
resultLabel->Text = "Cancelled";
}
else
{
// Finally, handle the case where the operation
// succeeded.
resultLabel->Text = e->Result->ToString();
}
// Enable the UpDown control.
this->numericUpDown1->Enabled = true;
// Enable the Start button.
startAsyncButton->Enabled = true;
// Disable the Cancel button.
cancelAsyncButton->Enabled = false;
}
// This event handler updates the progress bar.
void backgroundWorker1_ProgressChanged( Object^ /*sender*/, ProgressChangedEventArgs^ e )
{
this->progressBar1->Value = e->ProgressPercentage;
}
// This is the method that does the actual work. For this
// example, it computes a Fibonacci number and
// reports progress as it does its work.
long ComputeFibonacci( int n, BackgroundWorker^ worker, DoWorkEventArgs ^ e )
{
// The parameter n must be >= 0 and <= 91.
// Fib(n), with n > 91, overflows a long.
if ( (n < 0) || (n > 91) )
{
throw gcnew ArgumentException( "value must be >= 0 and <= 91","n" );
}
long result = 0;
// Abort the operation if the user has cancelled.
// Note that a call to CancelAsync may have set
// CancellationPending to true just after the
// last invocation of this method exits, so this
// code will not have the opportunity to set the
// DoWorkEventArgs.Cancel flag to true. This means
// that RunWorkerCompletedEventArgs.Cancelled will
// not be set to true in your RunWorkerCompleted
// event handler. This is a race condition.
if ( worker->CancellationPending )
{
e->Cancel = true;
}
else
{
if ( n < 2 )
{
result = 1;
}
else
{
result = ComputeFibonacci( n - 1, worker, e ) + ComputeFibonacci( n - 2, worker, e );
}
// Report progress as a percentage of the total task.
int percentComplete = (int)((float)n / (float)numberToCompute * 100);
if ( percentComplete > highestPercentageReached )
{
highestPercentageReached = percentComplete;
worker->ReportProgress( percentComplete );
}
}
return result;
}
void InitializeComponent()
{
this->numericUpDown1 = gcnew System::Windows::Forms::NumericUpDown;
this->startAsyncButton = gcnew System::Windows::Forms::Button;
this->cancelAsyncButton = gcnew System::Windows::Forms::Button;
this->resultLabel = gcnew System::Windows::Forms::Label;
this->progressBar1 = gcnew System::Windows::Forms::ProgressBar;
this->backgroundWorker1 = gcnew System::ComponentModel::BackgroundWorker;
(dynamic_cast<System::ComponentModel::ISupportInitialize^>(this->numericUpDown1))->BeginInit();
this->SuspendLayout();
//
// numericUpDown1
//
this->numericUpDown1->Location = System::Drawing::Point( 16, 16 );
array<Int32>^temp0 = {91,0,0,0};
this->numericUpDown1->Maximum = System::Decimal( temp0 );
array<Int32>^temp1 = {1,0,0,0};
this->numericUpDown1->Minimum = System::Decimal( temp1 );
this->numericUpDown1->Name = "numericUpDown1";
this->numericUpDown1->Size = System::Drawing::Size( 80, 20 );
this->numericUpDown1->TabIndex = 0;
array<Int32>^temp2 = {1,0,0,0};
this->numericUpDown1->Value = System::Decimal( temp2 );
//
// startAsyncButton
//
this->startAsyncButton->Location = System::Drawing::Point( 16, 72 );
this->startAsyncButton->Name = "startAsyncButton";
this->startAsyncButton->Size = System::Drawing::Size( 120, 23 );
this->startAsyncButton->TabIndex = 1;
this->startAsyncButton->Text = "Start Async";
this->startAsyncButton->Click += gcnew System::EventHandler( this, &FibonacciForm::startAsyncButton_Click );
//
// cancelAsyncButton
//
this->cancelAsyncButton->Enabled = false;
this->cancelAsyncButton->Location = System::Drawing::Point( 153, 72 );
this->cancelAsyncButton->Name = "cancelAsyncButton";
this->cancelAsyncButton->Size = System::Drawing::Size( 119, 23 );
this->cancelAsyncButton->TabIndex = 2;
this->cancelAsyncButton->Text = "Cancel Async";
this->cancelAsyncButton->Click += gcnew System::EventHandler( this, &FibonacciForm::cancelAsyncButton_Click );
//
// resultLabel
//
this->resultLabel->BorderStyle = System::Windows::Forms::BorderStyle::Fixed3D;
this->resultLabel->Location = System::Drawing::Point( 112, 16 );
this->resultLabel->Name = "resultLabel";
this->resultLabel->Size = System::Drawing::Size( 160, 23 );
this->resultLabel->TabIndex = 3;
this->resultLabel->Text = "(no result)";
this->resultLabel->TextAlign = System::Drawing::ContentAlignment::MiddleCenter;
//
// progressBar1
//
this->progressBar1->Location = System::Drawing::Point( 18, 48 );
this->progressBar1->Name = "progressBar1";
this->progressBar1->Size = System::Drawing::Size( 256, 8 );
this->progressBar1->Step = 2;
this->progressBar1->TabIndex = 4;
//
// backgroundWorker1
//
this->backgroundWorker1->WorkerReportsProgress = true;
this->backgroundWorker1->WorkerSupportsCancellation = true;
//
// FibonacciForm
//
this->ClientSize = System::Drawing::Size( 292, 118 );
this->Controls->Add( this->progressBar1 );
this->Controls->Add( this->resultLabel );
this->Controls->Add( this->cancelAsyncButton );
this->Controls->Add( this->startAsyncButton );
this->Controls->Add( this->numericUpDown1 );
this->Name = "FibonacciForm";
this->Text = "Fibonacci Calculator";
(dynamic_cast<System::ComponentModel::ISupportInitialize^>(this->numericUpDown1))->EndInit();
this->ResumeLayout( false );
}
};
[STAThread]
int main()
{
Application::Run( gcnew FibonacciForm );
}
import System.* ;
import System.Collections.* ;
import System.ComponentModel.* ;
import System.Drawing.* ;
import System.Threading.* ;
import System.Windows.Forms.* ;
public class FibonacciForm extends System.Windows.Forms.Form
{
private int numberToCompute = 0;
private int highestPercentageReached = 0;
private System.Windows.Forms.NumericUpDown numericUpDown1;
private System.Windows.Forms.Button startAsyncButton;
private System.Windows.Forms.Button cancelAsyncButton;
private System.Windows.Forms.ProgressBar progressBar1;
private System.Windows.Forms.Label resultLabel;
private System.ComponentModel.BackgroundWorker backgroundWorker1;
public FibonacciForm()
{
InitializeComponent();
InitializeBackgoundWorker();
} //FibonacciForm
// Set up the BackgroundWorker object by
// attaching event handlers.
private void InitializeBackgoundWorker()
{
backgroundWorker1.add_DoWork(new DoWorkEventHandler(
backgroundWorker1_DoWork));
backgroundWorker1.add_RunWorkerCompleted(
new RunWorkerCompletedEventHandler(
backgroundWorker1_RunWorkerCompleted));
backgroundWorker1.add_ProgressChanged(
new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged));
} //InitializeBackgoundWorker
private void startAsyncButton_Click(Object sender, EventArgs e)
{
// Reset the text in the result label.
resultLabel.set_Text(String.Empty);
// Disable the UpDown control until
// the asynchronous operation is done.
this.numericUpDown1.set_Enabled(false);
// Disable the Start button until
// the asynchronous operation is done.
this.startAsyncButton.set_Enabled(false);
// Enable the Cancel button while
// the asynchronous operation runs.
this.cancelAsyncButton.set_Enabled(true);
// Get the value from the UpDown control.
numberToCompute = System.Convert.ToInt32((numericUpDown1.get_Value()));
// Reset the variable for percentage tracking.
highestPercentageReached = 0;
// Start the asynchronous operation.
backgroundWorker1.RunWorkerAsync(System.Convert.ToString
(numberToCompute));
}
private void cancelAsyncButton_Click(Object sender, System.EventArgs e)
{
// Cancel the asynchronous operation.
this.backgroundWorker1.CancelAsync();
// Disable the Cancel button.
cancelAsyncButton.set_Enabled(false);
}
// This event handler is where the actual,
// potentially time-consuming work is done.
private void backgroundWorker1_DoWork(Object sender, DoWorkEventArgs e)
{
// Get the BackgroundWorker that raised this event.
BackgroundWorker worker = (BackgroundWorker)sender;
// Assign the result of the computation
// to the Result property of the DoWorkEventArgs
// object. This is will be available to the
// RunWorkerCompleted eventhandler.
e.set_Result(new Long(ComputeFibonacci(System.Convert.ToInt32
(e.get_Argument()), worker, e)));
//e.Result = ComputeFibonacci((int)e.Argument, worker, e);
} //backgroundWorker1_DoWork
// This event handler deals with the results of the
// background operation.
private void backgroundWorker1_RunWorkerCompleted(Object sender,
RunWorkerCompletedEventArgs e)
{
// First, handle the case where an exception was thrown.
if (e.get_Error() != null) {
MessageBox.Show(e.get_Error().get_Message());
}
else {
if (e.get_Cancelled()) {
// Next, handle the case where the user cancelled
// the operation.
// Note that due to a race condition in
// the DoWork event handler, the Cancelled
// flag may not have been set, even though
// CancelAsync was called.
resultLabel.set_Text("Cancelled");
}
else {
// Finally, handle the case where the operation
// succeeded.
resultLabel.set_Text(e.get_Result().ToString());
}
}
// Enable the UpDown control.
this.numericUpDown1.set_Enabled(true);
// Enable the Start button.
startAsyncButton.set_Enabled(true);
// Disable the Cancel button.
cancelAsyncButton.set_Enabled(false);
} //backgroundWorker1_RunWorkerCompleted
// This event handler updates the progress bar.
private void backgroundWorker1_ProgressChanged(Object sender,
ProgressChangedEventArgs e)
{
this.progressBar1.set_Value(e.get_ProgressPercentage());
} //backgroundWorker1_ProgressChanged
// This is the method that does the actual work. For this
// example, it computes a Fibonacci number and
// reports progress as it does its work.
long ComputeFibonacci(int n, BackgroundWorker worker, DoWorkEventArgs e)
{
// The parameter n must be >= 0 and <= 91.
// Fib(n), with n > 91, overflows a long.
if (n < 0 || n > 91) {
throw new ArgumentException("value must be >= 0 and <= 91", "n");
}
long result = 0;
// Abort the operation if the user has cancelled.
// Note that a call to CancelAsync may have set
// CancellationPending to true just after the
// last invocation of this method exits, so this
// code will not have the opportunity to set the
// DoWorkEventArgs.Cancel flag to true. This means
// that RunWorkerCompletedEventArgs.Cancelled will
// not be set to true in your RunWorkerCompleted
// event handler. This is a race condition.
if (worker.get_CancellationPending()) {
e.set_Cancel(true);
}
else {
if (n < 2) {
result = 1;
}
else {
result = ComputeFibonacci(n - 1, worker, e)
+ ComputeFibonacci(n - 2, worker, e);
}
// Report progress as a percentage of the total task.
int percentComplete=(int)((float)(n)/(float)(numberToCompute)* 100);
if (percentComplete > highestPercentageReached) {
highestPercentageReached = percentComplete;
worker.ReportProgress(percentComplete);
}
}
return result;
}
#region Windows Form Designer generated code
private void InitializeComponent()
{
this.numericUpDown1 = new System.Windows.Forms.NumericUpDown();
this.startAsyncButton = new System.Windows.Forms.Button();
this.cancelAsyncButton = new System.Windows.Forms.Button();
this.resultLabel = new System.Windows.Forms.Label();
this.progressBar1 = new System.Windows.Forms.ProgressBar();
this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker();
((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).
BeginInit();
this.SuspendLayout();
//
// numericUpDown1
//
this.numericUpDown1.set_Location(new System.Drawing.Point(16, 16));
this.numericUpDown1.set_Maximum(new System.Decimal(
new int[] { 91, 0, 0, 0 }));
this.numericUpDown1.set_Minimum(new System.Decimal(
new int[] { 1, 0, 0, 0 }));
this.numericUpDown1.set_Name("numericUpDown1");
this.numericUpDown1.set_Size(new System.Drawing.Size(80, 20));
this.numericUpDown1.set_TabIndex(0);
this.numericUpDown1.set_Value(new System.Decimal(
new int[] { 1, 0, 0, 0 }));
//
// startAsyncButton
//
this.startAsyncButton.set_Location(new System.Drawing.Point(16, 72));
this.startAsyncButton.set_Name("startAsyncButton");
this.startAsyncButton.set_Size(new System.Drawing.Size(120, 23));
this.startAsyncButton.set_TabIndex(1);
this.startAsyncButton.set_Text("Start Async");
this.startAsyncButton.add_Click(
new System.EventHandler(this.startAsyncButton_Click));
//
// cancelAsyncButton
//
this.cancelAsyncButton.set_Enabled(false);
this.cancelAsyncButton.set_Location(new System.Drawing.Point(153, 72));
this.cancelAsyncButton.set_Name("cancelAsyncButton");
this.cancelAsyncButton.set_Size(new System.Drawing.Size(119, 23));
this.cancelAsyncButton.set_TabIndex(2);
this.cancelAsyncButton.set_Text("Cancel Async");
this.cancelAsyncButton.add_Click(
new System.EventHandler(this.cancelAsyncButton_Click));
//
// resultLabel
//
this.resultLabel.set_BorderStyle(System.Windows.Forms.BorderStyle.Fixed3D);
this.resultLabel.set_Location(new System.Drawing.Point(112, 16));
this.resultLabel.set_Name("resultLabel");
this.resultLabel.set_Size(new System.Drawing.Size(160, 23));
this.resultLabel.set_TabIndex(3);
this.resultLabel.set_Text("(no result)");
this.resultLabel.set_TextAlign(System.Drawing.ContentAlignment.MiddleCenter);
//
// progressBar1
//
this.progressBar1.set_Location(new System.Drawing.Point(18, 48));
this.progressBar1.set_Name("progressBar1");
this.progressBar1.set_Size(new System.Drawing.Size(256, 8));
this.progressBar1.set_Step(2);
this.progressBar1.set_TabIndex(4);
//
// backgroundWorker1
//
this.backgroundWorker1.set_WorkerReportsProgress(true);
this.backgroundWorker1.set_WorkerSupportsCancellation(true);
//
// FibonacciForm
//
this.set_ClientSize(new System.Drawing.Size(292, 118));
this.get_Controls().Add(this.progressBar1);
this.get_Controls().Add(this.resultLabel);
this.get_Controls().Add(this.cancelAsyncButton);
this.get_Controls().Add(this.startAsyncButton);
this.get_Controls().Add(this.numericUpDown1);
this.set_Name("FibonacciForm");
this.set_Text("Fibonacci Calculator");
((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).
EndInit();
this.ResumeLayout(false);
} //InitializeComponent
#endregion
/** @attribute STAThread()
*/
public static void main(String[] args)
{
Application.Run(new FibonacciForm());
} //main
} //FibonacciForm
Compiling the Code
This example requires:
- References to the System, System.Drawing, and System.Windows.Forms assemblies.
For information about building this example from the command line for Visual Basic or Visual C#, see Building from the Command Line (Visual Basic) or Command-Line Building. You can also build this example in Visual Studio by pasting the code into a new project. How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio
Robust Programming
.gif) Caution |
|---|
When using multithreading of any sort, you potentially expose yourself to very serious and complex bugs. Consult the Managed Threading Best Practices before implementing any solution that uses multithreading. |
See Also
Reference
BackgroundWorker
DoWorkEventArgs
Concepts
Event-based Asynchronous Pattern Overview
Managed Threading Best Practices