尝试创建基于MVVM三层架构的异步任务：
场景：View层触发ViewModel层的动作请求，ViewModel层异步的从Model层查询数据，当数据返回或者请求超时时正确更新ViewModel层数据并触发View层的UI更新。
要求：View层保持UI响应，ViewModel层实现有超时控制的异步调用并返回结果
---------------------------
实现三个Worker，Worker1演示调用超时返回，Worker2演示无超时成功返回，Worker3演示同样演示无超时返回
设计WPF窗口如下：
<Window x:Class="TimeOutTask.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TimeOutTask"
Title="TaskTimeOutDemo" Height="480" Width="650">
<Window.DataContext>
<local:ViewModel></local:ViewModel>
</Window.DataContext>
<Window.Resources>
<Style TargetType="{x:Type Button}">
<Setter Property="Height" Value="30"></Setter>
<Setter Property="Margin" Value="5"></Setter>
<Setter Property="Width" Value="80"></Setter>
</Style>
<Style TargetType="{x:Type ListBox}">
<Setter Property="Height" Value="120"></Setter>
<Setter Property="Margin" Value="5"></Setter>
<Setter Property="Width" Value="500"></Setter>
</Style>
</Window.Resources>
<StackPanel>
<StackPanel Orientation="Horizontal">
<Button Command="{Binding Worker1Command}" Content="Start Worker1" />
<ListBox Background="LightGray" ItemsSource="{Binding Worker1StatusCollection}" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<Button Command="{Binding Worker2Command}" Content="Start Worker2" />
<ListBox Background="LightGray" ItemsSource="{Binding Worker2StatusCollection}"/>
</StackPanel>
<StackPanel Orientation="Horizontal">
<Button Command="{Binding Worker3Command}" Content="Start Worker3" />
<ListBox Background="LightGray" ItemsSource="{Binding Worker3StatusCollection}"/>
</StackPanel>
</StackPanel>
</Window>
ViewModel类设计如下：
其中 synchronizationContext
为UI线程的同步上下文，作为Task返回结果是的回调更新ViewModel层数据之用，注意:View层和ViewModel是同时运行在主线程之上的。
注意我们创建的实际工作task的方法是Task(Action action, TaskCreationOptions
creationOptions);
其中TaskCreationOptions
参数选择的是 TaskCreationOptions.LongRunning，此参数保证创建的task始终运行在同一个线程之上，减少线程间切换上下文的损失。
另外，传入timeout的方式是Task的方法public bool Wait(int
millisecondsTimeout);返回True时表示在规定时间内返回了结果，放回false表示未在指定时间内返回结果。
public class ViewModel : INotifyPropertyChanged
{
Model engineSimulator;
private SynchronizationContext synchronizationContext;
public ViewModel()
{
engineSimulator = new Model();
synchronizationContext = System.Threading.SynchronizationContext.Current;
worker1StatusCollection = new ObservableCollection<string>();
Worker1Command = new DelegateCommand(Worker1, () => !IsWorker1Busy);Worker2StatusCollection = new ObservableCollection<string>();
Worker2Command = new DelegateCommand(Worker2, () => !IsWorker2Busy);Worker3StatusCollection = new ObservableCollection<string>();
Worker3Command = new DelegateCommand(Worker3, () => !IsWorker3Busy);
}#region Worker1
private ObservableCollection<string> worker1StatusCollection;
public ObservableCollection<string> Worker1StatusCollection
{
get { return worker1StatusCollection; }
set { PropertyChanged.ChangeAndNotify(ref worker1StatusCollection, value, () => Worker1StatusCollection); }
}
public void Worker1()
{
Worker1StatusCollection.Add(string.Format("Start Worker1 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker1Busy = true;
((DelegateCommand)Worker1Command).RaiseCanExecuteChanged();
Task.Factory.StartNew((Action)(() =>
{
var longRunningTaskWithTimeout = new Task<string>(() =>
{
return engineSimulator.GetDataWithLongTime();
}, TaskCreationOptions.LongRunning);longRunningTaskWithTimeout.Start();
int miliSec = 5000;
if (longRunningTaskWithTimeout.Wait(miliSec))
{
synchronizationContext.Post(s =>
{
Worker1StatusCollection.Add(string.Format("Task completed with allotted time:{0}s" + miliSec / 1000));
Worker1StatusCollection.Add("Task Status:" + longRunningTaskWithTimeout.Status.ToString());
Worker1StatusCollection.Add("ResultFromEngine:"+longRunningTaskWithTimeout.Result);
Worker1StatusCollection.Add(string.Format("End Worker1 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker1Busy = false;
((DelegateCommand)Worker1Command).RaiseCanExecuteChanged();
}, null);
}
else
{
synchronizationContext.Post(s =>
{
Worker1StatusCollection.Add(string.Format("Task Not completed with allotted time:{0}s", miliSec / 1000));Worker1StatusCollection.Add("Status:" + longRunningTaskWithTimeout.Status.ToString());
Worker1StatusCollection.Add(string.Format("End Worker1 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker1Busy = false;
((DelegateCommand)Worker1Command).RaiseCanExecuteChanged();
}, null);
}
}));
}
private bool isWorker1Busy;
public bool IsWorker1Busy
{
get { return isWorker1Busy; }
set { PropertyChanged.ChangeAndNotify(ref isWorker1Busy, value, () => IsWorker1Busy); }
}
public ICommand Worker1Command { get; private set; }
#endregion#region Worker2
private ObservableCollection<string> worker2StatusCollection;
public ObservableCollection<string> Worker2StatusCollection
{
get { return worker2StatusCollection; }
set { PropertyChanged.ChangeAndNotify(ref worker2StatusCollection, value, () => Worker2StatusCollection); }
}
public void Worker2()
{
Worker2StatusCollection.Add(string.Format("Start Worker2 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker2Busy = true;
((DelegateCommand)Worker2Command).RaiseCanExecuteChanged();
Task.Factory.StartNew((Action)(() =>
{
var longRunningTaskWithTimeout = new Task<string>(() =>
{
return engineSimulator.GetDataWithLongTime();
}, TaskCreationOptions.LongRunning);longRunningTaskWithTimeout.Start();
int miliSec = 11000;
if (longRunningTaskWithTimeout.Wait(miliSec))
{
synchronizationContext.Post(s =>
{
Worker2StatusCollection.Add(string.Format("Task completed with allotted time:{0}s", miliSec / 1000));
Worker2StatusCollection.Add("Tast Status:" + longRunningTaskWithTimeout.Status.ToString());
Worker2StatusCollection.Add("ResultFromEngine:" + longRunningTaskWithTimeout.Result);
Worker2StatusCollection.Add(string.Format("End Worker2 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker2Busy = false;
((DelegateCommand)Worker2Command).RaiseCanExecuteChanged();
}, null);
}
else
{
synchronizationContext.Post(s =>
{
Worker2StatusCollection.Add(string.Format("Task Not completed with allotted time:{0}s", miliSec / 1000));
Worker2StatusCollection.Add("Task Status:" + longRunningTaskWithTimeout.Status.ToString());
Worker2StatusCollection.Add(string.Format("End Worker2 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker2Busy = false;
((DelegateCommand)Worker2Command).RaiseCanExecuteChanged();
}, null);
}
}));
}
private bool isWorker2Busy;
public bool IsWorker2Busy
{
get { return isWorker2Busy; }
set { PropertyChanged.ChangeAndNotify(ref isWorker2Busy, value, () => IsWorker2Busy); }
}
public ICommand Worker2Command { get; private set; }
#endregion#region Worker3
private ObservableCollection<string> worker3StatusCollection;
public ObservableCollection<string> Worker3StatusCollection
{
get { return worker3StatusCollection; }
set { PropertyChanged.ChangeAndNotify(ref worker3StatusCollection, value, () => Worker3StatusCollection); }
}
public void Worker3()
{
Worker3StatusCollection.Add(string.Format("Start Worker3 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker3Busy = true;
((DelegateCommand)Worker3Command).RaiseCanExecuteChanged();
Task.Factory.StartNew((Action)(() =>
{
var longRunningTaskWithTimeout = new Task<string>(() =>
{
return engineSimulator.GetDataWithShortTime();
}, TaskCreationOptions.LongRunning);longRunningTaskWithTimeout.Start();
int miliSec = 1000;
if (longRunningTaskWithTimeout.Wait(miliSec))
{
synchronizationContext.Post(s =>
{
Worker3StatusCollection.Add(string.Format("Task completed with allotted time:{0}s", miliSec / 1000));
Worker3StatusCollection.Add("Task Status:" + longRunningTaskWithTimeout.Status.ToString());
Worker3StatusCollection.Add("ResultFromEngine:" + longRunningTaskWithTimeout.Result);
Worker3StatusCollection.Add(string.Format("End Worker3 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker3Busy = false;
((DelegateCommand)Worker3Command).RaiseCanExecuteChanged();
}, null);
}
else
{
synchronizationContext.Post(s =>
{
Worker3StatusCollection.Add(string.Format("Task Not completed with allotted time:{0}", miliSec / 1000));
Worker3StatusCollection.Add("Status:" + longRunningTaskWithTimeout.Status.ToString());
Worker3StatusCollection.Add(string.Format("End Worker3 at:{0}", DateTime.Now.ToLongTimeString()));
IsWorker3Busy = false;
((DelegateCommand)Worker3Command).RaiseCanExecuteChanged();
}, null);
}
}));
}
private bool isWorker3Busy;
public bool IsWorker3Busy
{
get { return isWorker3Busy; }
set { PropertyChanged.ChangeAndNotify(ref isWorker3Busy, value, () => IsWorker3Busy); }
}
public ICommand Worker3Command { get; private set; }
#endregionpublic event PropertyChangedEventHandler PropertyChanged;
}
模仿Model层的类定义如下：一个方法等待10s模仿底层操作（Worker1，Worker2使用），另一个方法直接返回（供Worker3使用）
public class Model
{
public string GetDataWithLongTime()
{
Thread.Sleep(TimeSpan.FromSeconds(10));
return "Data from DataWithLongTime";
}
public string GetDataWithShortTime()
{
return "Data from DataWithShortTime";
}
}
基本的思想就是这样。
作者：Andy Zeng
欢迎任何形式的转载，但请务必注明出处。
http://www.cnblogs.com/andyzeng/p/3732156.html