Csharp 使用命令初始化可绑定属性

发布于03月21日

当属性更改时，有没有一种方法执行命令，指定的绑定延迟？

作为一个例子，让我们使用CheckBox，它具有属性Iscury，延迟= 1000(1秒)，以及当Iscury属性发生变化时调用的Command:

MainWindow.xaml:

<CheckBox Command="{Binding Command}"
          Content="Hello"
          IsChecked="{Binding IsChecked, Delay=1000}" />

MainWindow.xaml.cs:

private bool _isChecked;
public bool IsChecked
{
    get { return _isChecked; }
    set
    {
        if (_isChecked != value)
        {
            _isChecked = value;
            OnPropertyChanged();
            MessageBox.Show("Property Changed"); 
        }
    }
}

public ICommand Command { get; } = new RelayCommand(obj => MessageBox.Show("Command Invoked"));

当点击复选框时，首先调用MessageBox.Show("命令已删除")，然后调用MessageBox.Show("属性已更改")；

最终输出:

"Command Invoked" -\> after 1 sec delay -\> "Property Changed"

推荐答案

您可以从属性set()执行操作，具体取决于Binding的延迟.

或者使用计时器或Task.Delay显式延迟操作:

public ICommand SomeCommand { get; } = new RelayCommand(ExecuteSomeCommandDelayedAsync);

private async Task ExecuteSomeCommandDelayedAsync(object commandParameter)
{
  await Task.Delay(TimeSpan.FromSeconds(1));
  MessageBox.Show("Command Invoked");
}

要复制绑定引擎的延迟行为，您必须使用计时器，并在每次调用时重置它，并独占地遵守最新的更改/命令参数.

下面的示例使用System.Threading.Timer(如果您一般需要访问UI元素或DispatcherObject实例，则应改用DispatcherTimer):

public ICommand SomeCommand { get; } = new RelayCommand(ExecuteSomeCommand);

// Important: this Timer implements IDisposable/IDisposableAsync.
// It must be disposed if it is no longer needed!
private System.Threading.Timer CommandDelayTimer { get; } 
private object SomeCommandCommandParameter { get; set; }

public Constructor()
  => this.CommandDelayTimer = new Timer(OnCommandDelayElapsed);

private async Task ExecuteSomeCommand(object commandParameter)
{
  // Capture latest parameter value and drop the previous
  this.SomeCommandCommandParameter = commandParameter;

  // Start/reset the timer.
  // This timer is configured to execute only once (period time = 0).
  _ = this.CommandDelayTimer.Change(TimeSpan.FromSeconds(1), TimeSpan.Zero);
}

private void OnCommandDelayElapsed(object? state)
{
  SomeCommandOperation(state);
}

// The operation that the command is supposed to invoke after a delay
private void SomeCommandOperation(object commandParameter)
{  
  MessageBox.Show("Command Invoked");
}