C# async await 学习笔记2

C# async await 学习笔记1（http://www.cnblogs.com/siso/p/3691059.html）

提到了ThreadId是一样的，突然想到在WinForm中，非UI线程是无法直接更新UI线程上的控件的问题。

于是做了如下测试：

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{public Form1(){InitializeComponent();}Task<string> LongTimeTask(){tbResult.Text += "LongTimeTask开始:" + DateTime.Now.ToString() + "\r\n";             Task<string> task = new Task<string>(() => { Thread.Sleep(5000); return "这是任务返回值"; });task.Start();tbResult.Text += "LongTimeTask结束:" + DateTime.Now.ToString() + "\r\n";    return task;}async void AsyncCall(){tbResult.Text += "AsyncCall开始：" + DateTime.Now.ToString() + "\r\n";     string result = await LongTimeTask(); //await调用的方法需要返回Task或Task<T>，且调用await所在的方法要有async关键字tbResult.Text += "AsyncCall:" + result + "\r\n"; tbResult.Text += "AsyncCall结束：" + DateTime.Now.ToString() + "\r\n"; }   private void button1_Click(object sender, EventArgs e){tbResult.Text += "Main开始：" + DateTime.Now.ToString() + "\r\n";AsyncCall();tbResult.Text += "Main结束：" + DateTime.Now.ToString() + "\r\n";}}
}

发现，在AsyncCall中，可以直接访问TextBox（tbResult)，如果对上面的测试觉得没什么奇怪，大家可以先看下面的代码。

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;namespace WindowsFormsApplication1
{public partial class Form2 : Form{public Form2(){InitializeComponent();}void LongTimeTask(){Thread.Sleep(5000);tbResult.Text += "AsyncCall结束：" + DateTime.Now.ToString() + "\r\n";} private void button1_Click(object sender, EventArgs e){tbResult.Text += "Main开始：" + DateTime.Now.ToString() + "\r\n";Thread t = new Thread(LongTimeTask);t.Start();tbResult.Text += "Main结束：" + DateTime.Now.ToString() + "\r\n";}}
}

运行到 LongTimeTask的tbResult.Text时，提示：线程间操作无效: 从不是创建控件“tbResult”的线程访问它。

为了能在非UI线程中访问到UI线程中的控件，于是需作如下修改：

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;namespace WindowsFormsApplication1
{public partial class Form2 : Form{delegate void UpdateUIDelegate();UpdateUIDelegate updateUIDelegate;        public Form2(){InitializeComponent();updateUIDelegate = new UpdateUIDelegate(UpdateUI);}void UpdateUI(){if (tbResult.InvokeRequired){tbResult.Invoke(updateUIDelegate);}else{tbResult.Text += "AsyncCall结束：" + DateTime.Now.ToString() + "\r\n";}}void LongTimeTask(){Thread.Sleep(5000);UpdateUI();        } private void button1_Click(object sender, EventArgs e){tbResult.Text += "Main开始：" + DateTime.Now.ToString() + "\r\n";Thread t = new Thread(LongTimeTask);t.Start();tbResult.Text += "Main结束：" + DateTime.Now.ToString() + "\r\n";}}
}