Question

我试过编写简单的WinForm应用程序，我的行为有问题。目的是在面板上绘制两个可选颜色（红色和黑色）的小矩形。有4个按钮 - 每种颜色配对 - 绘制红色，停止红色，绘制黑色，停止黑色。

点击绘图按钮后，会生成 DrawRectangles 的新任务。单击停止按钮后，将使用CancellationTokenSource取消任务。

问题是：当我创建了许多任务（即绘制红色的3个任务）之后我按下了停止按钮，它只取消了第一个任务，我无法取消其他任务（绘制红色任务' ）他们跑得无穷无尽。

以下代码：

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);
    }
}

我想要做的是当我点击停止按钮时，所有相同颜色的正在运行的任务都将被取消。

更新正如法比奥建议的那样，我已经重写了我的点击方法以及受影响的方法。在那之后，它可以按照需要运行。

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

问题的根源在于，如果您单击运行任务的按钮3次，则您将使用3种不同的取消令牌源运行3个任务。

由于RunDrawingTask中的这一行，您将覆盖刚刚传递给RunDrawingTask的取消令牌

cnTokenSource = new CancellationTokenSource();

如果您删除该行，则每次都会传递相同的令牌，并且您的所有任务都可以对取消作出反应。

Answer 2

您的逻辑对您的要求无效。解决方案之一：您需要创建两个CancelationTokenSources：redCancelationTokenSource和blackCancelationokenSource。并重写RunDrawingTask方法，如下所示：

    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);

当你想要停止绘制动作时，你必须在CancelationTokenSources之一上调用'Cancel'方法：redCancelationSource或blackCancelationSource。

控制和取消多个任务

2 个答案: