摘要:Silverlight MultiThreading
多線程對開發和用戶體驗的重要性不言而喻,Silverlight BCL 幾乎提供了完整的 Thread Class。
1. Dispatcher
和 WPF / WinForm 一樣,我們只能在 UI Thread 中更新顯示控件屬性。多線程編碼時,需要借助於 Dispatcher。
private void Button_Click(object sender, RoutedEventArgs e)
{
new Thread(() =>
{
this.Dispatcher.BeginInvoke(() =>
{
this.TextBlock1.Text = DateTime.Now.ToString();
});
}).Start();
}
在類庫中可以用 Deployment.Current.Dispatcher 來獲取 Dispatcher 引用。
private void Button_Click(object sender, RoutedEventArgs e)
{
new Thread(() =>
{
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
this.TextBlock1.Text = DateTime.Now.ToString();
});
}).Start();
}
當然,也可以用同步上下文來完成類似操作。
private void Button_Click(object sender, RoutedEventArgs e)
{
var context = SynchronizationContext.Current;
new Thread(() =>
{
context.Send((s) =>
{
this.TextBlock1.Text = DateTime.Now.ToString();
}, null);
}).Start();
}
2. ThreadPool
Silverlight ThreadPool 默認線程數量為:
WorkerThreads: 2 ~ 500
CompletionPortThreads: 2 ~ 1000
使用方法和以往並無兩樣。
private void Button_Click(object sender, RoutedEventArgs e)
{
ThreadPool.QueueUserWorkItem((s) =>
{
this.Dispatcher.BeginInvoke(() =>
{
int minWorkerThreads, minCompletionPortThreads, maxWorkerThreads, maxCompletionPortThreads;
ThreadPool.GetMinThreads(out minWorkerThreads, out minCompletionPortThreads);
ThreadPool.GetMaxThreads(out maxWorkerThreads, out maxCompletionPortThreads);
this.TextBox1.Text = String.Format("WorkerThreads = {0} ~ {1}, CompletionPortThreads = {2} ~ {3}",
minWorkerThreads, maxWorkerThreads, minCompletionPortThreads, maxCompletionPortThreads);
});
});
}
需要注意的是:儘管 ThreadPool 提供了 SetMinThreads 、SetMaxThreads 方法,但卻無法使用,調用會觸發異常。
說到線程池,自然會想到委託的異步調用,不過這同樣是個問題。
In Silverlight, using delegates to make asynchronous method calls is not supported. Calling BeginInvoke causes a NotSupportedException.
3. WaitHandle
等待句柄是多線程編程必不可少的裝備。
public partial class MainPage : UserControl
{
AutoResetEvent handle = new AutoResetEvent(true);
public MainPage()
{
InitializeComponent();
new Thread(() =>
{
while (true)
{
handle.WaitOne();
this.Dispatcher.BeginInvoke(() =>
{
this.TextBlock1.Text = DateTime.Now.ToString();
});
}
}).Start();
}
private void Button_Click(object sender, RoutedEventArgs e)
{
handle.Set();
}
}
4. Timer
System.Thread.Timer 是一種多線程定時器。
public partial class MainPage : UserControl
{
Timer timer;
public MainPage()
{
InitializeComponent();
timer = new Timer((state) =>
{
this.Dispatcher.BeginInvoke(() =>
{
this.TextBlock1.Text = DateTime.Now.Ticks.ToString();
});
}, null, 0, 100);
}
}
TimerCallback 是在線程池中執行的,這意味著它並不會等待事件代碼執行完成就會觸發下一次事件,完全取決於代碼執行時間是否小於間隔時間。
另外還有一個 System.Windows.Threading.DispatcherTimer,它直接使用 Dispatcher Queue 來執行事件代碼,因此可以直接更新界面元素。
public partial class MainPage : UserControl
{
DispatcherTimer timer;
public MainPage()
{
InitializeComponent();
timer = new DispatcherTimer();
timer.Tick += (s, e) => { this.TextBlock1.Text = DateTime.Now.ToString(); };
timer.Interval = TimeSpan.FromMilliseconds(1000);
timer.Start();
}
}