[同步]Invoke
Application.Current.Dispatcher.Invoke(AutoIncreaseNumber);
[异步]BeginInvoke
Application.Current.Dispatcher.BeginInvoke((Action)AutoIncreaseNumber);
两者都会阻塞UI线程
基于WPF4.5.1示例
Invoke 按钮对应的是InvokeCommand
BeginInvoke按钮对应的是BeginInvokeCommand
可以发现，在执行按钮的命令时，UI线程是会阻塞，计时器并不会走动
public class MainViewModel : ViewModelBase
{
public MainViewModel()
{
DispatcherTimer timer = new DispatcherTimer();
timer.Interval = TimeSpan.FromSeconds();
timer.Tick += timer_Tick;
timer.Start();
} void timer_Tick(object sender, EventArgs e)
{
Now = DateTime.Now;
} private DateTime now = DateTime.Now; public DateTime Now
{
get { return now; }
set
{
now = value;
RaisePropertyChanged("Now");
}
} private int number;
/// <summary>
/// 数值用于显示
/// </summary>
public int Number
{
get { return number; }
set
{
number = value;
RaisePropertyChanged("Number");
}
} private bool isIncrease;
/// <summary>
/// 是否可以自增长
/// </summary>
public bool IsIncrease
{
get { return isIncrease; }
set
{
isIncrease = value;
RaisePropertyChanged("IsIncrease");
}
} /// <summary>
/// 自动增长
/// </summary>
private void AutoIncreaseNumber()
{
IsIncrease = !isIncrease;
while (IsIncrease && Number < )
{
Number++;
}
} #region RelayCommands
/// <summary>
/// Invoke命令
/// </summary>
public RelayCommand InvokeCommand
{
get
{
return new RelayCommand(() =>
{
Application.Current.Dispatcher.Invoke(AutoIncreaseNumber);
});
}
}
/// <summary>
/// BeginInvoke命令
/// </summary>
public RelayCommand BeginInvokeCommand
{
get
{
return new RelayCommand(() =>
{
//这里直接使用匿名方法会报错
//'Cannot convert lambda expression to type 'System.Delegate' because it is not a delegate type'
//使用强制转换的方式
Application.Current.Dispatcher.BeginInvoke((Action)AutoIncreaseNumber);
});
}
}
/// <summary>
/// 清理数字命令
/// </summary>
public RelayCommand ClearCommand
{
get
{
return new RelayCommand(() =>
{
Number = ;
IsIncrease = false;
});
}
}
#endregion
}
注：其中阻塞UI线程的原因是把Number的递增放到了Dispather中去执行，如果想要不阻塞，那么需要有一个新的DispatcherTimer的对象去执行这个递增的逻辑，那么就不会阻塞UI线程了。
所以说这里所说的异步并不是相对于UI线程的异步，那么究竟是什么？
Invoke 是同步操作；因此，直到回调返回之后才会将控制权返回给调用对象。
BeginInvoke 是异步操作；因此，调用之后控制权会立即返回给调用对象。
--- msdn
做一个测试
/// <summary>
/// DiffInInvokeAndBeginInvoke.xaml 的交互逻辑
/// </summary>
public partial class DiffInInvokeAndBeginInvoke : Window
{
public DiffInInvokeAndBeginInvoke()
{
InitializeComponent();
this.ltb.ItemsSource = _infos;
this.Loaded += DiffInInvokeAndBeginInvoke_Loaded;
} private ObservableCollection<string> _infos = new ObservableCollection<string>(); private void DiffInInvokeAndBeginInvoke_Loaded(object sender, RoutedEventArgs e)
{
ExcuteMethod();
ExcuteMethod_2();
ExcuteMethod_3();
} private void ExcuteMethod()
{
Dispatcher.Invoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.SystemIdle, "1-1: SystemIdle Invoke");
Dispatcher.Invoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Send, "1-2: Send Invoke ");
Dispatcher.BeginInvoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Normal, "1-3: Normal BeginInvoke");
Dispatcher.BeginInvoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Send, "1-4: Send BeginInvoke");
DispatcherOperation dop = Dispatcher.BeginInvoke(new Action<string>(PrintInformation), "1-5: Defaut BeginInvoke");
} private void ExcuteMethod_2()
{ Dispatcher.BeginInvoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Normal, "2-1: Normal BeginInvoke");
Dispatcher.Invoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Send, "2-2: Send Invoke ");
Dispatcher.BeginInvoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Send, "2-3: Send BeginInvoke");
} private void ExcuteMethod_3()
{
Dispatcher.Invoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Send, "3-1: Send Invoke ");
Dispatcher.BeginInvoke(new Action<string>(PrintInformation), System.Windows.Threading.DispatcherPriority.Send, "2-2: Send BeginInvoke");
} private void PrintInformation(string info)
{
_infos.Add(info);
}
}
结果如下：
从结果及MSDN对于Invoke及BeginInvoke的解释，很容易就理解了。
Invoke一定要执行完了才会执行下去，而BeginInvoke是没有等待执行完就接着往下走了，然后会根据线程的调用优先级开始执行。