如何实现非ui线程更新ui线程？

1. 实现非ui线程更新ui线程的代码

2. 编码中出现的一个错误及探究

<1>. 实现非ui线程更新ui线程

之前的基本做法是使用Invoke实现，这里采用的是 .net 4.0中的Task来实现，代码如下：

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

using System.Threading.Tasks;

using System.Threading;

namespace WindowsFormsApplication1 {

public partial class Form1 : Form {

private readonly TaskScheduler m_syncContextScheduler = null;

public Form1() {

InitializeComponent();

base.Text = "Synchronization context task scheduler demo";

base.Visible = true;

base.Height = 100;

base.Width = 400;

// 属性m_syncContextScheduler需要在这里初始化

m_syncContextScheduler =

TaskScheduler.FromCurrentSynchronizationContext();

}

private CancellationTokenSource cts;

private TaskScheduler context = TaskScheduler.Current;

// 计算

private Int32 Sum(CancellationToken token, Int32 n) {

Int32 sum = 0;

for (Int32 i = 1; i <= n; ++i) {

// 出于演示目的，这里休眠一段时间

Thread.Sleep(1000);

sum += i;

}

return sum;

}

protected override void OnMouseClick(MouseEventArgs e) {

if (this.cts != null) {

// 开始取消操作

cts.Cancel();

this.cts = null;

}

else {

// 操作还没有开始，启动任务

this.Text = "Operation running";

this.cts = new CancellationTokenSource();

var t = new Task<Int32>

(

() => Sum(cts.Token, 10),

cts.Token

);

t.Start();

// 如果该任务结束的话，启动新任务，更新ui线程

t.ContinueWith(task => Text = "Result :" + t.Result,

CancellationToken.None,

TaskContinuationOptions.OnlyOnRanToCompletion,

this.m_syncContextScheduler);

// 如果是取消的话

t.ContinueWith(task => Text = "Operation cancel",

CancellationToken.None,

TaskContinuationOptions.OnlyOnCanceled,

this.m_syncContextScheduler);

// 如果出现错误

t.ContinueWith(task => this.Text = "Operation cancel",

CancellationToken.None,

TaskContinuationOptions.OnlyOnFaulted,

this.m_syncContextScheduler);

}

base.OnMouseClick(e);

}

}

}

<2>. 编码中出现的错误及探究

最初的代码将m_syncContextScheduler对象是通过下面的语句产生的：

private readonly TaskScheduler m_syncContextScheduler =

TaskScheduler.FromCurrentSynchronizationContext();

debug时，产生如下错误：

通过异常信息可以看出这可能是当前初始化还为完成，那么这就引出c#中构造函数初始化和属性的初始化顺序的问题，通过调试或者是查看生成的il代码发现了问题所在，c#中首先执行

private TaskScheduler m_syncContextScheduler =
TaskScheduler.FromCurrentSynchronizationContext();

此时环境还没有初始话完成。il中更加明显：

.method public hidebysig specialname rtspecialname

instance void .ctor() cil managed

{

// Code size 87 (0x57)

.maxstack 2

IL_0000: ldarg.0

IL_0001: ldnull

IL_0002: stfld class [System]System.ComponentModel.IContainer WindowsFormsApplication1.Form1::components

IL_0007: ldarg.0

IL_0008: call class [mscorlib]System.Threading.Tasks.TaskScheduler [mscorlib]System.Threading.Tasks.TaskScheduler::FromCurrentSynchronizationContext()

IL_000d: stfld class [mscorlib]System.Threading.Tasks.TaskScheduler WindowsFormsApplication1.Form1::m_syncContextScheduler

IL_0012: ldarg.0

IL_0013: call class [mscorlib]System.Threading.Tasks.TaskScheduler [mscorlib]System.Threading.Tasks.TaskScheduler::get_Current()

IL_0018: stfld class [mscorlib]System.Threading.Tasks.TaskScheduler WindowsFormsApplication1.Form1::context

IL_001d: ldarg.0
// 初始化，调用form构造函数

IL_001e: call instance void [System.Windows.Forms]System.Windows.Forms.Form::.ctor()