Question

我创建了一个带有按钮的新UserContol。我想将button命令绑定到新用户控件的dependancy属性，如下所示。

<Grid>
 <Button Name="Button1" Command="{Binding Button1Command}" />
</Grid>

这是包含UserControl的DP：

public ICommand Button1Command
{
  get { return (ICommand)GetValue(Button1CommandProperty); }
  set { SetValue(Button1CommandProperty, value); }
}

public static readonly DependencyProperty Button1CommandProperty =
    DependencyProperty.Register("Button1Command", typeof(ICommand), typeof(BptCellTemplate), new FrameworkPropertyMetadata(null));

当我尝试使用它时按下按钮没有任何反应。它无法识别该命令。如果我添加一个事件就行了。像这样：

 public static readonly DependencyProperty Button1CommandProperty =
    DependencyProperty.Register("Button1Command", typeof(ICommand), typeof(BptCellTemplate), new FrameworkPropertyMetadata(null, OnButton1CommandChanged));

private static void OnButton1CommandChanged(DependencyObject dependencyObject,
                                              DependencyPropertyChangedEventArgs args)
{
  var bptCellTemplate = dependencyObject as BptCellTemplate;
  if (bptCellTemplate == null || !(args.NewValue is ICommand))
  {
    return;
  }
  (bptCellTemplate.DataContext as BptCellTemplateViewModel).Button1Command = (ICommand)args.NewValue;

}

有没有办法在没有事件的情况下绑定它？因为它适用于其他按钮属性，我以相同的方式（例如Visibility）

Answer 1

您的绑定可能无效，因为没有任何内容表明Button1Command属性是您UserControl的成员。

在Visual Studio中调试程序时，可以通过查看“输出”窗口来确认这是问题所在。您可能会看到未找到成员Button1Command的绑定错误。

典型的解决方法是为UserControl的根元素添加名称属性，例如x:Name="root"（如果有的话，可以选择自己的名称或使用现有名称）。然后，将绑定更改为命令以引用新名称：

<Button Name="Button1" Command="{Binding Button1Command, ElementName=root}" />

Answer 2

您需要类实现ICommand接口。

public class RelayCommand : ICommand
{
    #region Fields

    readonly Action<object> _execute;
    readonly Predicate<object> _canExecute;

    #endregion // Fields

    #region Constructors

    /// <summary>
    /// Creates a new command that can always execute.
    /// </summary>
    /// <param name="execute">The execution logic.</param>
    public RelayCommand(Action<object> execute)
        : this(execute, null)
    {
    }

    /// <summary>
    /// Creates a new command.
    /// </summary>
    /// <param name="execute">The execution logic.</param>
    /// <param name="canExecute">The execution status logic.</param>
    public RelayCommand(Action<object> execute, Predicate<object> canExecute)
    {
        if (execute == null)
            throw new ArgumentNullException("execute");

        _execute = execute;
        _canExecute = canExecute;
    }

    #endregion // Constructors

    #region ICommand Members

    [DebuggerStepThrough]
    public bool CanExecute(object parameter)
    {
        return _canExecute == null ? true : _canExecute(parameter);
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }

    #endregion // ICommand Members
}

现在绑定非常简单。在DataContext中定义命令（MVVM等）不记得设置DataContext ...例如DataContext = this; （这是你的窗口）

RelayCommand _btnCommand;
public ICommand Button1Command
{
    get
    {
        if (_btnCommand == null)
        {
            _btnCommand = new RelayCommand(param => this.ExecuteButton1(),
                param => this.CanButton1());
        }
        return _btnCommand;
    }
}

public void ExecuteButton1()
{
}

public bool CanButton1()
{
    return true;
}

就是这样......

按钮命令绑定不起作用

2 个答案: