重新想象 Windows 8 Store Apps (44)
[源码下载]重新想象 Windows 8 Store Apps (44) - 多线程之异步编程: 经典和最新的异步编程模型, IAsyncInfo 与 Task 相互转换
作者：webabcd
介绍
重新想象 Windows 8 Store Apps 之 异步编程
[*]经典的异步编程模型（IAsyncResult）
[*]最新的异步编程模型（async 和 await）
[*]将 IAsyncInfo 转换成 Task
[*]将 Task 转换成 IAsyncInfo
示例
1、使用经典的异步编程模型（IAsyncResult）实现一个支持异步操作的类
Thread/Async/ClassicAsync.cs
/*
* 使用经典的异步编程模型（IAsyncResult）实现一个支持异步操作的类
*/
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace XamlDemo.Thread.Async
{
public class ClassicAsync
{
private delegate string HelloDelegate(string name);
private HelloDelegate _helloDelegate;
public ClassicAsync()
{
_helloDelegate = new HelloDelegate(Hello);
}
private string Hello(string name)
{
new ManualResetEvent(false).WaitOne(3000);
return "hello: " + name;
}
// begin 方法
public IAsyncResult BeginRun(string name, AsyncCallback callback, Object state)
{
// 新开线程，去执行 Hello() 方法，callback 是回调，state 是上下文
return _helloDelegate.BeginInvoke(name, callback, state);
}
// end 方法
public string EndRun(IAsyncResult ar)
{
if (ar == null)
throw new NullReferenceException("IAsyncResult 不能为 null");
return _helloDelegate.EndInvoke(ar);
}
}
}
Thread/Async/ClassicAsyncDemo.xaml
Thread/Async/ClassicAsyncDemo.xaml.cs
/*
* 演示如何通过经典的异步编程模型（IAsyncResult）来进行异步操作
*
* IAsyncResult - 异步操作结果
* AsyncState - 上下文
* IsCompleted - 异步操作是否已完成
* AsyncWaitHandle -获取用于等待异步操作完成的 System.Threading.WaitHandle 对象（通过 WaitHandle.WaitOne() 在当前线程等待）
*/
using System;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
namespace XamlDemo.Thread.Async
{
public sealed partial class ClassicAsyncDemo : Page
{
System.Threading.SynchronizationContext _syncContext;
public ClassicAsyncDemo()
{
this.InitializeComponent();
// 获取当前 UI 线程
_syncContext = System.Threading.SynchronizationContext.Current;
}
private void btnIAsyncResult_Click_1(object sender, RoutedEventArgs e)
{
ClassicAsync classicAsync = new ClassicAsync();
IAsyncResult ar = classicAsync.BeginRun("webabcd", new AsyncCallback(Callback), classicAsync);
lblMsg.Text = "开始执行，3 秒后完成";
}
private void Callback(IAsyncResult ar)
{
ClassicAsync classicAsync = (ClassicAsync)ar.AsyncState;
string result = classicAsync.EndRun(ar);
_syncContext.Post(
(ctx) =>
{
lblMsg.Text = result;
},
null);
}
}
}
2、演示如何通过最新的异步编程模型（async 和 await）来进行异步操作
Thread/Async/NewAsyncDemo.xaml
Thread/Async/NewAsyncDemo.xaml.cs
/*
* 演示如何通过最新的异步编程模型（async 和 await）来进行异步操作
*
* 注：
* 1、要想 await，其所在方法必须标记为 async
* 2、方法被标记为 async 是为了让编译器重新编写该方法，使 await 中的内容重新编写为具有 GetAwaiter() 等实际异步逻辑的代码
*/
using System;
using System.Threading;
using System.Threading.Tasks;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
namespace XamlDemo.Thread.Async
{
public sealed partial class NewAsyncDemo : Page
{
private static int _count = 0;
public NewAsyncDemo()
{
this.InitializeComponent();
}
// 不带返回值的 Task
private async Task TaskWithoutReturn()
{
// 在另一个线程 sleep 1000 毫秒，然后回到 UI 线程
await Task.Delay(1000);
// await Task.Delay(Timeout.Infinite); 长眠于此
// await Task.Delay(Timeout.InfiniteTimeSpan); 长眠于此
// 直接在当前线程 sleep 可以使用如下方法，因为 WinRT 中没有 Thread.Sleep() 了
// new ManualResetEvent(false).WaitOne(1000);
Interlocked.Increment(ref _count);
}
// 带返回值的 Task
private async Task TaskWithReturn()
{
await Task.Delay(1000);
Interlocked.Increment(ref _count);
return _count;
}
// 演示不带返回值的异步操作
private async void btnTaskWithoutReturn_Click_1(object sender, RoutedEventArgs e)
{
// ConfigureAwait(false) - 异步操作后不返回 UI 线程，可节省一点点资源。默认值：ConfigureAwait(true)
await TaskWithoutReturn().ConfigureAwait(false);
lblMsg.Text = "count: " + _count.ToString();
}
// 演示带返回值的异步操作
private async void btnTaskWithReturn_Click_1(object sender, RoutedEventArgs e)
{
int result = await TaskWithReturn();
lblMsg.Text = "count: " + result.ToString();
}
// 演示多任务并行执行的异步操作
private async void btnMultiTask_Click_1(object sender, RoutedEventArgs e)
{
Task task = Task.WhenAll(TaskWithoutReturn(), TaskWithoutReturn(), TaskWithoutReturn());
DateTime dt = DateTime.Now;
await task;
lblMsg.Text = "count: " + _count.ToString() + ", 执行时间: " + (DateTime.Now - dt).TotalSeconds.ToString() + "秒";
}
// 演示如何执行一个不 await 的 Task
private void btnTaskWithoutAwait_Click_1(object sender, RoutedEventArgs e)
{
// 让 task 在新线程执行去吧，本线程不管它是什么执行情况
Task task = TaskWithoutReturn();
lblMsg.Text = "count: " + _count.ToString();
}
}
}
3、演示如何将 IAsyncInfo（IAsyncAction, IAsyncOperation, IAsyncActionWithProgress, IAsyncOperationWithProgress） 转成 Task
Thread/Async/IAsyncInfo2Task.xaml
Thread/Async/IAsyncInfo2Task.xaml.cs
/*
* 演示如何将 IAsyncInfo（IAsyncAction, IAsyncOperation, IAsyncActionWithProgress, IAsyncOperationWithProgress） 转成 Task
*/
using System;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;
namespace XamlDemo.Thread.Async
{
public sealed partial class IAsyncInfo2Task : Page
{
public IAsyncInfo2Task()
{
this.InitializeComponent();
}
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
// 用于取消 Task
CancellationTokenSource cts = new CancellationTokenSource();
// 创建一个 IAsyncInfo
IAsyncOperation action = AsyncInfo.Run(
(token) =>
Task.Run(
() =>
{
token.WaitHandle.WaitOne(3000);
token.ThrowIfCancellationRequested();
return 10 * 10;
},
token));
lblMsg.Text = "开始执行，3 秒后完成";
// 将 IAsyncOperation 转换成 Task
// AsTask() 是扩展方法，其逻辑在 System.WindowsRuntimeSystemExtensions 类中
Task task = action.AsTask(cts.Token);
int result = await task;
lblMsg.Text = "结果：" + result.ToString();
}
}
}
4、演示如何将 Task 转成 IAsyncInfo（IAsyncAction, IAsyncOperation）
Thread/Async/Task2IAsyncInfo.xaml
Thread/Async/Task2IAsyncInfo.xaml.cs
/*
* 演示如何将 Task 转成 IAsyncInfo（IAsyncAction, IAsyncOperation）
*/
using System;
using System.Threading;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;
namespace XamlDemo.Thread.Async
{
public sealed partial class Task2IAsyncInfo : Page
{
public Task2IAsyncInfo()
{
this.InitializeComponent();
}
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
// 用于取消 IAsyncInfo（注意：本例中的 IAsyncInfo 是从 Task 转换过来的，所以 IAsyncInfo.Cancel() 方法无效）
CancellationTokenSource cts = new CancellationTokenSource();
// 创建一个 Task
Task task = Task.Run(
() =>
{
cts.Token.WaitHandle.WaitOne(3000);
cts.Token.ThrowIfCancellationRequested();
return 10 * 10;
},
cts.Token);
lblMsg.Text = "开始执行，3 秒后完成";
// 将 Task 转换成 IAsyncOperation
// AsAsyncAction(), AsAsyncOperation() 是扩展方法，其逻辑在 System.WindowsRuntimeSystemExtensions 类中
IAsyncOperation operation = task.AsAsyncOperation();
int result = await operation;
lblMsg.Text = "结果：" + result.ToString();
}
}
}
OK
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