我是 C# 和面向对象编程的新手。我一直在尝试在我的 GUI 中实现一个“取消”按钮,以便用户可以在过程中停止它。
我阅读了这个问题:How to implement a Stop/Cancel button? 并确定 backgroundWorker 对我来说应该是一个不错的选择,但是给出的示例没有解释如何将参数传递给 backgroundWorker。
我的问题是我不知道如何将参数传递给 backgroundWorker 以使其停止进程;我只能让 backgroundWorker 停止自己。
我创建了以下代码来尝试了解这一点,其中我的表单有两个按钮(buttonStart 和 buttonStop)和一个 backgroundWorker(backgroundWorkerStopCheck):
using System;
using System.ComponentModel;
using System.Windows.Forms;
using System.Threading;
using System.Timers;
namespace TestBackgroundWorker
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
// Set the background worker to allow the user to stop the process.
backgroundWorkerStopCheck.WorkerSupportsCancellation = true;
}
private System.Timers.Timer myTimer;
private void backgroundWorkerStopCheck_DoWork(object sender, DoWorkEventArgs e)
{
//If cancellation is pending, cancel work.
if (backgroundWorkerStopCheck.CancellationPending)
{
e.Cancel = true;
return;
}
}
private void buttonStart_Click(object sender, EventArgs e)
{
// Notify the backgroundWorker that the process is starting.
backgroundWorkerStopCheck.RunWorkerAsync();
LaunchCode();
}
private void buttonStop_Click(object sender, EventArgs e)
{
// Tell the backgroundWorker to stop process.
backgroundWorkerStopCheck.CancelAsync();
}
private void LaunchCode()
{
buttonStart.Enabled = false; // Disable the start button to show that the process is ongoing.
myTimer = new System.Timers.Timer(5000); // Waste five seconds.
myTimer.Elapsed += new ElapsedEventHandler(myTimer_Elapsed);
myTimer.Enabled = true; // Start the timer.
}
void myTimer_Elapsed(object sender, ElapsedEventArgs e)
{
buttonStart.Enabled = true; // ReEnable the Start button to show that the process either finished or was cancelled.
}
}
}
如果代码运行正常,则在用户单击“开始”后重新启用“开始”按钮之前,代码将在那里停留 5 秒钟,或者如果用户单击“停止”,则将快速重新激活“开始”按钮。
这段代码有两个我不知道如何处理的问题:
1) “myTimer_Elapsed”方法在尝试启用“开始”按钮时导致 InvalidOperationException,因为“跨线程操作无效”。如何避免跨线程操作?
2)现在 backgroundWorker 没有完成任何事情,因为我不知道如何向它提供参数,以便在取消时它会停止计时器。
我很感激任何帮助!
最佳答案
首先,避免“跨线程操作无效”的问题是在控件上使用 Invoke 。您不能使用来自不同线程的控件。
关于第二个问题,我会按照下面的方式来实现。这是具有取消支持的最小后台 worker 实现。
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
namespace WindowsFormsApplication5
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
// Set the background worker to allow the user to stop the process.
backgroundWorkerStopCheck.WorkerSupportsCancellation = true;
backgroundWorkerStopCheck.DoWork += new DoWorkEventHandler(backgroundWorkerStopCheck_DoWork);
}
private void backgroundWorkerStopCheck_DoWork(object sender, DoWorkEventArgs e)
{
try
{
for (int i = 0; i < 50; i++)
{
if (backgroundWorkerStopCheck.CancellationPending)
{
// user cancel request
e.Cancel = true;
return;
}
System.Threading.Thread.Sleep(100);
}
}
finally
{
InvokeEnableStartButton();
}
}
private void buttonStart_Click(object sender, EventArgs e)
{
//disable start button before launch work
buttonStart.Enabled = false;
// start worker
backgroundWorkerStopCheck.RunWorkerAsync();
}
private void buttonStop_Click(object sender, EventArgs e)
{
// Tell the backgroundWorker to stop process.
backgroundWorkerStopCheck.CancelAsync();
}
private void InvokeEnableStartButton()
{
// this method is called from a thread,
// we need to Invoke to avoid "cross thread exception"
if (this.InvokeRequired)
{
this.Invoke(new EnableStartButtonDelegate(EnableStartButton));
}
else
{
EnableStartButton();
}
}
private void EnableStartButton()
{
buttonStart.Enabled = true;
}
}
internal delegate void EnableStartButtonDelegate();
}
关于向工作线程传递参数,您可以在
RunWorkerAsync()
方法中传递任何对象,并在 backgroundWorkerStopCheck_DoWork
方法中重新定义: ...
backgroundWorkerStopCheck.RunWorkerAsync("hello");
...
private void backgroundWorkerStopCheck_DoWork(object sender, DoWorkEventArgs e)
{
string argument = e.Argument as string;
// argument value is "hello"
...
}
希望能帮助到你。
关于c# - 将参数传递给 backgroundWorker(用作取消按钮),我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/8155166/