C# 异步 async 和 await

1、 页面头部 <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" Async="true" %>

2、 

protected async void Button1_Click(object sender, EventArgs e)
{
//TextBox1.Text = new Class1().Start();

int contentLength = await AccessTheWebAsync();    //这里会阻塞后面的执行
TextBox1.Text += "1245";
TextBox1.Text += contentLength;
}

async Task<int> AccessTheWebAsync()  // 这里的返回值类型 Task<T> void  Task
{
HttpClient client = new HttpClient();
Task<string> getStringTask = client.GetStringAsync("http://msdn.microsoft.com");

DoIndependentWork();

string urlContent = await getStringTask;

return urlContent.Length;

}

void DoIndependentWork()
{
TextBox1.Text += "Working.......";
}

第二种方式:

public string Start()
{
Diaplay();   //这里不会阻止线程执行
return result.ToString() + "12454";
}

public async void Diaplay()
{
double result = await GetValueAsync(124.12, 1.122);

}

Task<double> GetValueAsync(double num1, double num2)
{
return Task.Run(() =>
{
for (int i = 0; i < 10000; i++)
{
num1 = num1 / num2;
}
return num1;
});
}