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(); 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();

            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();
            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";
        }
    }
}