如何停止Backgroundworker并关闭表单？

Question

我想完全停止BackgroundWorker DoWork（）过程，同时运行关闭窗体。

我已经应用了下面的代码，但在“this.Invoke”中会引发错误：“调用或BeginInvoke无法在控件上调用，直到窗口句柄被创建。”同时形成关闭。

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) 
     { 
      var dt_Images = db.Rings.Select(I => new { I.PaidRs, I.TypeID, I.RingID, I.CodeNo, Image = Image.FromStream(new MemoryStream(I.Image.ToArray())) }).OrderByDescending(r => r.TypeID); 
      foreach (var dr in dt_Images.ThenByDescending(r => r.RingID).ToList()) 
      { 
       BTN = new Button(); 
       BTN.TextImageRelation = TextImageRelation.TextAboveImage; 
       BTN.TextAlign = System.Drawing.ContentAlignment.BottomCenter; 
       BTN.AutoSize = true; 
       BTN.Name = dr.RingID.ToString(); 
       BTN.Image = dr.Image; 
       BTN.Text = dr.CodeNo.ToString() + " " + dr.TypeID.ToString(); 
       this.Invoke(new MethodInvoker(delegate { if (backgroundWorker1 != null) flowLayoutPanel1.Controls.Add(BTN); else return; })); 
       BTN.Click += new EventHandler(this.pic_Click); 
       this.Invoke(new MethodInvoker(delegate { if (backgroundWorker1 == null) txt_pcs.Text = flowLayoutPanel1.Controls.Count.ToString(); else return;})); 
      } 
     } 

    private void Form_KeyDown(object sender, KeyEventArgs e) 
     { 
      if (e.KeyData == Keys.Escape) 
      { 
       backgroundWorker1.CancelAsync(); //backgroundworker doesnt stop here 
       backgroundWorker1 = null; //it still invokes the delegate 
       this.Dispose(); 
      } 
     } 

如何解决此错误？

请帮帮我。

Answer 1

实际的问题是，在后台线程调用Invoke之前，没有办法安全地检查表单是否正在关闭。

要做到这一点，你可以做的是推迟关闭一点，直到后台线程有机会退出主循环。

首先，声明两个标志和一个锁对象：

private volatile bool _closeRequest = false; 
private volatile bool _workerStopped = false; 
private readonly object _lock = new object(); 

然后，当你想关闭的形式，只需拨打Close：

private void Form_KeyDown(object sender, KeyEventArgs e) 
{ 
    if (e.KeyData == Keys.Escape) 
    { 
     Close(); 
    } 
} 

里面FormClosing，检查是否劳动者已停止。这部分必须是显示器内部，以防止在后台线程只是被完成了比赛条件（即确保_workerStopped和_closeRequest是原子更新）：

protected override void OnFormClosing(FormClosingEventArgs e) 
{ 
    lock (_lock) 
    { 
     // if not stopped 
     if (!_workerStopped) 
     { 
      // delay closing 
      e.Cancel = true; 

      // notify worker 
      _closeRequest = true; 
     } 
    } 
    base.OnFormClosing(e); 
} 

最后，在你的后台线程，实际关闭如果需要的形式：

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) 
{ 
    try 
    { 
     foreach (var dr in GetImages()) 
     { 
      if (_closeRequest) 
       break; 

      // ... do stuff 
     } 
    } 
    finally 
    { 
     lock (_lock) 
     { 
      // notify we stopped 
      _workerStopped = true; 

      // if closing was postponed, close now 
      if (_closeRequest) 
       BeginInvoke(new MethodInvoker(Close)); 
     } 
    } 
} 

Answer 2

里面你必须开始处理下一个图像之前要检查你的backgroundWorker1.CancellationPending方法的DoWork。

在允许用户关闭表单之前，您必须等待处理完最后一张图像。

有关如何使用CancellationPending和Cancel性能comlete例子中看到this MSDN example

Answer 3

你必须注意你的工人里面的取消请求。像

private void DoWork(object sender, DoWorkEventArgs e) 
{ 
var worker = sender as BackgroundWorker; 

while (!worker.CancellationPending) 
{ 
    … 
} 

if (worker.CancellationPending) 
{ 
    e.Cancel = true; 
} 
} 

Answer 4

这里有一个简单的程序，我想，一定会给你的同时BackgroundWorker运行如何采用这样的形式的关闭的护理的想法：

int i = 0;//This is to show progress. 
bool cancel;//This is to notify RunWorkerCompleted to Close() the Form if needed. 

public Form1() 
{ 
    InitializeComponent(); 
    FormClosing += Form1_FormClosing; 

    backgroundWorker1.WorkerSupportsCancellation = true; 
    backgroundWorker1.RunWorkerCompleted += backgroundWorker1_RunWorkerCompleted; 
    backgroundWorker1.RunWorkerAsync(); 
} 

void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) 
{ 
    //Since this is executed on the main thread - it is not (as far as I know) going to "race" against the FormClosing. 
    if (cancel) Close(); 
    else Text = "Done"; 
} 

void Form1_FormClosing(object sender, FormClosingEventArgs e) 
{ 
    if (backgroundWorker1.IsBusy) 
    { 
     cancel = true; 
     backgroundWorker1.CancelAsync(); 
     e.Cancel = true; 
    } 
} 

private void button1_Click(object sender, EventArgs e) 
{ 
    backgroundWorker1.CancelAsync(); 
} 

//This is executed on a separate thread: 
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) 
{ 
    while (!backgroundWorker1.CancellationPending) 
    { 
     Invoke((Action)(() => Text = (i++).ToString())); 
     Thread.Sleep(1000); 
    } 
    e.Cancel = true; 
}