控制和取消多项任务

Question

我尝试编写简单的 WinForm 应用程序，但我对其行为有一些问题。目的是在面板上绘制具有两种可选颜色（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、止黑.

当点击Draw按钮时，会生成新的DrawRectangles任务。单击停止按钮时，将使用 CancellationTokenSource 取消任务。

问题是：当我创建了很多任务（即绘制红色的 3 个任务）并且在我按下停止按钮之后，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')，它们运行无穷无尽。

下面的代码：

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运行任务将被取消。

更新： 正如 Fabio 所建议的，我已经重写了我的点击方法以及受影响的方法。在那之后它会按需要工作。

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

你的问题的根源在于，如果你点击 3 次运行任务按钮，你将运行 3 个任务与 3 个不同的取消令牌源。

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，您每次都会传递相同的令牌，您的所有任务都将能够对取消做出反应。

Answer 2

您的逻辑不符合您的要求。解决方案之一：您需要创建两个 CancellationTokenSources：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);

并且当您想要停止绘图操作时，您必须在 CancellationTokenSources 之一上调用 'Cancel' 方法：redCancelationSource 或 blackCancelationSource。

控制和取消多项任务

Control and cancel multiple tasks

c#

winforms

task-parallel-library