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BackgroundWorker 组件用来执行诸如数据库事务、文件下载等耗时的异步操作。

开始

在应用程序中添加一个BackgroundWorker实例,如果用的是VS,可以从工具上直接拖到应用程序:

BackgroundWorker backgroundWorker1 = new BackgroundWorker();

为了开始在后台操作,必须调用BackgroundWorker的RunWorkerAsync()方法,当调用此方时,BackgroundWorker 通过触发DoWork 事件,开始执行后台操作,DoWork 事件的代码是在另一个线程里执行的。代码如下:

代码一:

BackgroundWorker backgroundWorker1 = new BackgroundWorker();

//在另一个线程里开始操作(btnStart是一个按钮控件)

//也可以利用RunWokerAsync()方法传递参数,

private void btnStart_Click(object sender, EventArgs e)

{

          backgroundWorker1.RunWokerAsync(2000/*参数是可选的*/);

}

//DoWork事件在另一个线程里执行

private void backgroundWorker1_DoWork(objectsender,DoWorkeventArgs e)

{

        //允许长时间的操作

        int input = (int)e.Argument;

        Thread.Sleep(input);

}

显示后台操作进度

为了显示后台操作的执行进度,首先要使WorkerReportsProgress 等于true,然后调用BackgroundWorker的ReportProgress()方法,通过它传递操作完成的进度值,此外,该方法触发ProgressChanged事件,在是此事件中,通过ProgressChangedEventArgs的实例,接收到主线程传递过来的参数。

代码二:

BackgroundWorker backgroundWorker1 = new BackgroundWorker();

backgroundWorker1.WorkerReportsProgress = true;

private void btnStart_Click(object sender, EventArgs e)

{

            backgroundWorker1.RunWokerAsync();

}

private void backgroundWorker1_DoWork(object sender, DoWorkeventArgs e)

{

      for (int i = 1; i < 11; i++)

     {

              Thread.Sleep(2000);

             backgroundWorker1.ReportProgress(i*10);

     }

}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)

{

      //progressBar1是ProgressBar控件

      progressBar1.Value = e.ProgressPercentage;

}

取消后台操作

为了使 BackgroundWorker 可以取消后台正在执行的操作,首先要把属性WorkerSupportsCancellation 的值设置为 true。接着调用CancelAsync()方法,该方法使得属性CancellationPending 为true,利用CancellationPending 属性,可以判断是否取消后台异步操作。

代码三:

BackgroundWorker backgroundWorker1 = new BackgroundWorker();

backgroundWorker1.WorkerReportsProgress = true;

backgroundWorker1.WorkerSupportsCancellation = true;

private void btnStart_Click(object sender, EventArgs e)

{

       backgroundWorker1.RunWokerAsync();

}

private void btnCancel_Click(object sender, EventArgs e)

{

      backgroundWorker1.CancelAsync();

}

private void backgroundWorker1_DoWork(object sender, DoWorkeventArgs e)

{

      for (int i = 1; i < 11; i++)

     {

             Thread.Sleep(2000);

             backgroundWorker1.ReportProgress(i*10);

            if(backgroundWorker1.CancellationPending)

            {

                   e.Cancel = true;

                   return;

             }

      }

}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)

{

         progressBar1.Value = e.ProgressPercentage;

}

 

后台操作完成后,反馈给用户

当后台操作完成以后,无论是completed 还是cancelled,则RunWorkerCompleted 事件被触发,通过此方法可以将后台操作的完成结果反馈给用户;

另外,通过RunWorkerCompletedEventArgs实例的Cancelled 属性,以判断是否是Cancel操作使得后台操作终止;

代码片段:

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)

{

if(e.Cancelled)

{

       MessageBox.Show("Operation Cancelled");

}

else

{

       MessageBox.Show("OperationCompleted");

}

}

从后台操作返回值

在执行DoWork 事件时,DoWorkEventArgs 实例的Result 属性,返回值到用户;在RunWorkerCompleted 事件里,RunWorkerCompletedEventArgs 实例的Result 属性接收值;

代码片段:

private void backgroundWorker1_DoWork(object sender, DoWorkeventArgs e)

{

Thread.Sleep(2000);

//在此处设置返回值

e.Result = 10;

}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)

{

//在此处接收传递回来的值

int returnValue = (int)e.Result;

}

 

结束

 

posted on 2009-10-12 23:30  inforasc  阅读(47373)  评论(10编辑  收藏  举报