控制和取消多個任務

Question

我試着編寫簡單的WinForm應用程序，並且我的行爲有問題。 目的是用兩種可選顏色（紅色&黑色）在面板上繪製小矩形。有4個按鈕 - 一對用於每個顏色 - 繪製紅色，停止紅色，繪製黑色，停止黑色。

當繪製按鈕被點擊時，的新任務繪製矩形被生成。 當停止按鈕被點擊時，任務將被取消，使用CancellationTokenSource。

問題是：當我創建了很多任務（即繪製紅色的3個任務）之後，我按下了停止按鈕，它取消了第一個任務，我無法取消其他任務（繪製紅色任務'），他們跑得無止境。

下面的代碼：

public partial class Form1 : Form 
{ 
    CancellationTokenSource cnDrawRedToken; 
    CancellationTokenSource cnDrawBlackToken; 
    public Form1() 
    { 
     InitializeComponent();   
    } 

    private void Form1_Load(object sender, EventArgs e{} 

    private void panel1_Paint(object sender, PaintEventArgs e){} 

    private void RedBtn_Click(object sender, EventArgs e) 
    { 
     RunDrawingTask(SetSpecificPen(Color.Red),out this.cnDrawRedToken);   
    } 

    private async Task DrawRectangles(int height, int width, Random random, Rectangle rectangle, Pen blackPen, CancellationToken cnToken) 
    { 
     while(true) 
     { 
      if (cnToken.IsCancellationRequested) 
       return; 
      rectangle.x = random.Next(0, width); 
      rectangle.y = random.Next(0, height); 
      this.panel1.CreateGraphics().DrawRectangle(blackPen, rectangle.x, rectangle.y, rectangle.width, rectangle.height); 
      //Thread.Sleep(200); 
      await Task.Delay(150); 
     } 
    } 

    private Pen SetSpecificPen(Color color) 
    { 
     Pen blackPen = new Pen(color, 2); 
     return blackPen; 
    } 

    private Rectangle InitRectangleWidthAndHeights() 
    { 
     Rectangle rectangle = new Rectangle(); 

     rectangle.width = 10; 
     rectangle.height = 10; 
     return rectangle; 
    } 

    private void StpRedBtn_Click(object sender, EventArgs e) 
    { 
     if (this.cnDrawRedToken != null) 
     { 
      this.cnDrawRedToken.Cancel(); 
      this.cnDrawRedToken = null; 
     } 
     else 
     { 
      this.cnDrawRedToken = new CancellationTokenSource(); 
     } 
    } 

    private void BlackBtn_Click(object sender, EventArgs e) 
    { 
     RunDrawingTask(SetSpecificPen(Color.Black),out this.cnDrawBlackToken); 
    } 

    private void StpBlkBtn_Click(object sender, EventArgs e) 
    { 
     if (this.cnDrawBlackToken != null) 
     { 
      this.cnDrawBlackToken.Cancel(); 
      this.cnDrawBlackToken = null; 
     } 
    } 

    private void RunDrawingTask(Pen specificPen, out CancellationTokenSource cnTokenSource) 
    { 
     int height = this.panel1.Height; 
     int width = this.panel1.Width; 
     Random random = new Random(); 
     Rectangle rectangle = InitRectangleWidthAndHeights(); 

     cnTokenSource = new CancellationTokenSource(); 
     CancellationTokenSource cts = cnTokenSource; 
     Task t = Task.Factory.StartNew(() => DrawRectangles(height, width, random, rectangle, specificPen, cts.Token), cts.Token); 
    } 
} 

，當我在停止按鈕顏色相同的所有正在運行的任務將被取消單擊我想要做的是。

更新： 由於法比奧建議，我已經重寫了我的點擊方法以及受影響的方法。在這之後，它會按需要工作。

public Form1() 
    { 
     InitializeComponent(); 
     cnDrawRedToken = new CancellationTokenSource() ; 
     cnDrawBlackToken = new CancellationTokenSource(); 
    } 
private void RedBtn_Click(object sender, EventArgs e) 
    { 
     if (this.cnDrawRedToken.IsCancellationRequested) 
     { 
      this.cnDrawRedToken = null; 
      this.cnDrawRedToken = new CancellationTokenSource(); 
     }   
     RunDrawingTask(SetSpecificPen(Color.Red), this.cnDrawRedToken);   
    } 
private void StpRedBtn_Click(object sender, EventArgs e) 
    { 
     if (this.cnDrawRedToken != null) 
     { 
      this.cnDrawRedToken.Cancel(); 
     }   
    } 

    private void BlackBtn_Click(object sender, EventArgs e) 
    { 
     if (this.cnDrawBlackToken.IsCancellationRequested) 
     { 
      this.cnDrawBlackToken = null; 
      this.cnDrawBlackToken = new CancellationTokenSource(); 
     }    
     RunDrawingTask(SetSpecificPen(Color.Black), this.cnDrawBlackToken); 
    } 

    private void StpBlkBtn_Click(object sender, EventArgs e) 
    { 
     if (this.cnDrawBlackToken != null) 
     { 
      this.cnDrawBlackToken.Cancel();     
     } 
    } 

    private void RunDrawingTask(Pen specificPen, CancellationTokenSource cnTokenSource) 
    { 
     int height = this.panel1.Height; 
     int width = this.panel1.Width; 
     Random random = new Random(); 
     Rectangle rectangle = InitRectangleWidthAndHeights(); 

     Task t = Task.Factory.StartNew(() => DrawRectangles(height, width, random, rectangle, specificPen, cnTokenSource.Token), cnTokenSource.Token); 
    } 

Answer 1

問題的根源在於，如果您單擊3次運行任務的按鈕，您將使用3種不同的取消標記源運行3個任務。

因爲這條線在RunDrawingTask，你會覆蓋您剛剛傳遞給RunDrawingTask

cnTokenSource = new CancellationTokenSource(); 

如果你刪除了這一行的取消標記，你每次都會經過同樣的道理，和你的任務將能夠對取消作出反應。

Answer 2

您的邏輯對您的要求無效。解決方案之一： 您需要創建兩個CancelationTokenSources：redCancelationTokenSource和blackCancelationokenSource。並改寫RunDrawingTask方法是這樣的：

private void RunDrawingTask(Pen pen, out CancellationTokenSource cnTokenSource) 
    { 
     int height = panel1.Height; 
     int width = panel1.Width; 
     Random random = new Random(); 
     Rectangle rectangle = InitRectangleWidthAndHeights(); 

     var cts = pen == blackPen ? blackTokenSource : redTokenSource; 
     Task.Factory.StartNew(() => DrawRectangles(height, width, random, rectangle, pen, cts.Token), cts.Token); 
    } 

    CancellationTokenSource blackTokenSource = new CancellationTokenSource(); 
    CancellationTokenSource redTokenSource = new CancellationTokenSource(); 

    Pen blackPen = new Pen(Color.Black); 
    Pen redPen = new Pen(Color.Red); 

，當你想停下來吸引你必須調用行動CancelationTokenSources的一個「取消」的方法：redCancelationSource或blackCancelationSource。