轉至:http://www.cnblogs.com/oec2003/archive/2009/12/20/1628412.html
相關問題:c#中使用多線程訪問winform中控件的若干問題
我所修改的動態顯示數據代碼:
Thread thr = new Thread(new ThreadStart(delegate()
{
while (true)
{
Thread.Sleep(100);
try
{
this.Invoke(new Action(delegate() { label1.Text = DateTime.Now.ToString(); }));
}
catch
{
}
}
}));
thr.IsBackground = true;
thr.Start();
以下代碼佔用CPU資源過高
ThreadPool.QueueUserWorkItem(new WaitCallback(delegate(object o)
{
while (true)
{
this.Invoke(new Action(delegate() { label1.Text = DateTime.Now.ToString(); }));
}
}));
資料如下:
在開發Window應用程序的時候,經常需要在界面上顯示出已經執行到什麼步驟了,拿一個簡單例子來說,創建一個Winform程序,在窗體上訪一個Button和一個Label,點擊Button時做100次循環,在Label上實時顯示當前循環的次數。一種簡單的做法就是使用Application.DoEvents,代碼如下:
private void btnTest_Click(object sender, EventArgs e) { for (int i = 0; i < 100; i++) { Thread.Sleep(100); label1.Text = i + "/100"; Application.DoEvents(); } }
上面的代碼如果將Application.DoEvents();去掉當點擊Button時,程序會卡住,直到這個循環執行完成,當這個循環足夠大時是不能忍受的。不過小數據量用Application.DoEvents()還行,數據量大了使用Application.DoEvents()就會帶來性能的問題。所以Application.DoEvents()要慎用,在大數據量的時候可以使用多線程解決。如下:
private void btnTest_Click(object sender, EventArgs e) { Thread thread = new Thread(new ThreadStart(DoWork)); thread.Start(); } private void DoWork() { for (int i = 0; i < 100; i++) { Thread.Sleep(100); label1.Text = i + "/100"; } }
嗯?出現異常了是吧,沒錯上面的代碼運行後後會出現“線程間操作無效: 從不是創建控件“label1”的線程訪問它。”的異常。關於什麼原因造成的,大家可以google一下。不過上面代碼在vs03中貌似可以正常運行。將代碼改成下面這樣就可以正常運行了:
private void btnTest_Click(object sender, EventArgs e) { Thread thread = new Thread(new ThreadStart(DoWork)); thread.Start(); } private void DoWork() { for (int i = 0; i < 100; i++) { Thread.Sleep(100); this.Invoke(new Action<string>(this.ChangeLabel),i.ToString()); } } private void ChangeLabel(string i) { label1.Text = i + "/100"; }
如果嫌多寫一個ChangeLabel方法費事,可以寫成匿名方法的形式,如下:
private void btnTest_Click(object sender, EventArgs e) { Thread thread = new Thread(new ThreadStart(DoWork)); thread.Start(); } private void DoWork() { for (int i = 0; i < 100; i++) { Thread.Sleep(100); this.Invoke(new Action(delegate(){label1.Text=i+"/100";})); } }
同樣可以使用匿名方法的方式將DoWork方法也去掉:
private void btnTest_Click(object sender, EventArgs e) { Thread thread = new Thread(new ThreadStart(delegate() { for (int i = 0; i < 100; i++) { Thread.Sleep(100); this.Invoke(new Action(delegate() { label1.Text = i + "/100"; })); } })); thread.Start(); }
如果想傳參數到Dowork方法中,那麼就不能使用ThreadStart類了,應該使用ParameterizedThreadStart類,如下:
private void btnTest_Click(object sender, EventArgs e) { string name = "oec2003"; Thread thread = new Thread(new ParameterizedThreadStart(DoWork)); thread.Start(name); } private void DoWork(object name) { for (int i = 0; i < 100; i++) { Thread.Sleep(100); this.Invoke(new Action(delegate(){label1.Text=name+":"+ i+"/100";})); } }
同樣我們也可以使用線程池的方式來實現
private void btnTest_Click(object sender, EventArgs e) { ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork)); } private void DoWork(object o) { for (int i = 0; i < 100; i++) { Thread.Sleep(100); this.Invoke(new Action(delegate(){label1.Text=i+"/100";})); } }
使用匿名方法的方式:
private void btnTest_Click(object sender, EventArgs e) { ThreadPool.QueueUserWorkItem(new WaitCallback(delegate(object o) { for (int i = 0; i < 100; i++) { Thread.Sleep(100); this.Invoke(new Action(delegate() { label1.Text = i + "/100"; })); } })); }