61.异步编程1 C#例子 WPF例子

和普通的任务绑定不太相同的部分如下：

 public MainWindowViewModel(){FetchUserInfoCommand = new RelayCommand(async (param) => await FetchUserInfoAsync());}private async Task FetchUserInfoAsync(){// 模拟异步操作，比如网络请求await Task.Delay(2000); // 模拟网络延迟UserInfo = "用户信息：新员工，需要学会WPF的异步，并巩固之前的知识。";}

        public MainWindowViewModel(){FetchUserInfoCommand = new RelayCommand(param => FetchUserInfoAsync());}//private async Task FetchUserInfoAsync()private void FetchUserInfoAsync(){Thread.Sleep(1000);UserInfo = "用户信息：新员工，需要学会WPF的异步，并巩固之前的知识。";}

前者是异步，后者则是普通的绑定任务。在前台实现的功能完全相同。但是后者却会导致前台卡死。

后台代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data.Common;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
using static System.Runtime.InteropServices.JavaScript.JSType;namespace 异步
{public class MainWindowViewModel : INotifyPropertyChanged{private string _userInfo;public string UserInfo{get { return _userInfo; }set{_userInfo = value;OnPropertyChanged(nameof(UserInfo));}}public ICommand FetchUserInfoCommand { get; }//public MainWindowViewModel()//{//    //FetchUserInfoCommand = new RelayCommand(async (param) => await FetchUserInfoAsync());//    FetchUserInfoCommand = new RelayCommand(param => FetchUserInfoAsync());//}private async Task FetchUserInfoAsync()//private void FetchUserInfoAsync()//{//    // 模拟异步操作，比如网络请求//    //await Task.Delay(2000); // 模拟网络延迟//    Thread.Sleep(1000);//    UserInfo = "用户信息：新员工，需要学会WPF的异步，并巩固之前的知识。";//}public MainWindowViewModel(){FetchUserInfoCommand = new RelayCommand(async (param) => await FetchUserInfoAsync());}private async Task FetchUserInfoAsync(){// 模拟异步操作，比如网络请求await Task.Delay(2000); // 模拟网络延迟UserInfo = "用户信息：新员工，需要学会WPF的异步，并巩固之前的知识。";}//固定public event PropertyChangedEventHandler PropertyChanged;protected void OnPropertyChanged([CallerMemberName] string propertyName = null){PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));}}public class RelayCommand : ICommand{private readonly Action<object> _execute;public event EventHandler CanExecuteChanged;public RelayCommand(Action<object> execute) => _execute = execute;public bool CanExecute(object parameter) => true; // 总是可执行（简化）public void Execute(object parameter) => _execute(parameter);}
}

using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;namespace 异步
{/// <summary>/// Interaction logic for MainWindow.xaml/// </summary>public partial class MainWindow : Window{public MainWindow(){InitializeComponent();DataContext=new MainWindowViewModel();}}
}

前台：

<Window x:Class="异步.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local="clr-namespace:异步"mc:Ignorable="d"Title="MainWindow" Height="450" Width="800"><Grid><StackPanel><Button Content="获取用户信息" Command="{Binding FetchUserInfoCommand}" Margin="10"/><TextBox Text="{Binding UserInfo, UpdateSourceTrigger=PropertyChanged}" Margin="10,20,10,10" TextWrapping="Wrap" Height="100"/></StackPanel></Grid>
</Window>