控制和取消多个任务

Question

我尝试编写简单的 WinForm 应用程序，但它的行为有些问题。 目的是在面板上用两种可选颜色（红色和黑色）绘制小矩形。有 4 个按钮 - 每种颜色对 - 画红色、停止红色、画黑色、停止黑色。

当点击Draw按钮时，会生成DrawRectangles的新任务。 当停止按钮被点击时，任务将被取消，使用 CancellationTokenSource。

问题是：当我创建了许多任务（即绘制红色的 3 个任务）之后，我按下停止按钮，它只取消了第一个任务，而我无法取消其他任务（绘制红色任务' ) 然后他们跑得没完没了。

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会被取消。

更新： 正如法比奥建议的那样，我重写了我的点击方法以及受影响的方法。之后，它可以按需要工作。

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

您的逻辑不符合您的要求。解决方案之一： 您需要创建两个 CancelationTokenSource：redCancelationTokenSource 和 blackCancelationokenSource。并像这样重写RunDrawingTask 方法：

    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);

当您想停止绘制动作时，您必须在 CancelationTokenSources 之一上调用“取消”方法：redCancelationSource 或 blackCancelationSource。

Answer 2

问题的根源在于，如果您单击运行任务的按钮 3 次，您将使用 3 个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，您将每次传递相同的令牌，并且您的所有任务都将能够对取消做出反应。