我如何通过一个变量作为CommandParameter [英] How do I pass a variable as a CommandParameter

问题描述

我想从视图模型发送一个变量作为参数的命令。命令如下：

I'm trying to send a variable from the ViewModel as a parameter to a command. The command looks like this:

public class EditPersonCommand : ICommand
{
  private bool _CanExecute = false;

  public bool CanExecute(object parameter)
  {
     PersonModel p = parameter as PersonModel;
     CanExecuteProperty = (p != null) && (p.Age > 0);
     return CanExecuteProperty;
  }

  public event EventHandler CanExecuteChanged;

  public void Execute(object parameter) { }

  private bool CanExecuteProperty
  {
     get { return _CanExecute; }
     set
     {
        if (_CanExecute != value)
        {
           _CanExecute = value;
           EventHandler can_execute = CanExecuteChanged;
           if (can_execute != null)
           {
              can_execute.Invoke(this, EventArgs.Empty);
           }
        }
     }
  }
}

该视图模型是这样的：

public class PersonViewModel : ViewModelBase
{
  private PersonModel _PersonModel;
  private EditPersonCommand _EditPersonCommand;

  ///<remarks>
  /// must use the parameterless constructor to satisfy <Window.Resources>
  ///</remarks>
  public PersonViewModel()
     : this(new PersonModel())
  {

  }

  public PersonViewModel(PersonModel personModel)
  {
     _PersonModel = personModel;
  }

  public ICommand EditPersonCommand
  {
     get
     {
        if (_EditPersonCommand == null)
        {
           _EditPersonCommand = new EditPersonCommand();
        }
        return _EditPersonCommand;
     }
  }
}

XAML中看起来是这样的：

The xaml looks like this:

<Button Content="Edit" HorizontalAlignment="Right" Height="20" Width="80"
   Command="{Binding EditPersonCommand}" 
   CommandParameter="{Binding _PersonModel}" />

我试图创造视图模型的属性，而不是使用私有局部变量的名字，但没有工作无论是。 空的对象参数总是显示在调用 CanExecute 与该按钮从未启用。如果我改变了 CommandParameter 值您好，然后我收到您好在调用 CanExecute ，所以我不知道为什么变量不工作。 。任何帮助，将不胜感激。

I've tried creating a property in the ViewModel instead of using the private local variable name, but that didnt work either. The object parameter always shows null in the call to CanExecute and the button is never enabled. If I change the CommandParameter value to Hello, then I receive Hello in the call to CanExecute, so I'm not sure why the variable doesnt work. Any help would be appreciated.

更新：我也试图使公共财产的模型（这我真的不希望公开该模式，但只是试图，看是否它的工作原理，但它不）。

Update: I've also tried making a public property to the model (which I dont really want to expose the model, but just tried it to see if it works, but it doesnt).

// Added this to the ViewModel
public PersonModel PersonModelProp
{
  get
  {
     return _PersonModel;
  }
  set
  {
     _PersonModel = value;
     OnPropertyChanged("PersonModelProp");
  }
}

和改变了XAML这样：

And changed the xaml to this:

<Button Content="Edit" HorizontalAlignment="Right" Height="20"  Width="80"
   Command="{Binding EditPersonCommand}" 
   CommandParameter="{Binding PersonModelProp}" />

但仍然没有运气。该视图模型不落实 INotifyPropertyChanged的

推荐答案

是CommandParameter总是空或有你只检查正在执行它的第一次？

Is the CommandParameter always null or are you only checking the first time it is being executed?

目前看来，在你在这种情况下，因为设置Command属性声明你的属性事项秩序导致CanExecute到。火之前立即CommandParameter已设置

It appears that the order in which you declare your properties matters in this case since setting the Command property causes the CanExecute to fire immediately before the CommandParameter has been set.

试命令属性之前移动CommandParameter属性：

Try moving the CommandParameter property before the Command property:

<Button Content="Edit" HorizontalAlignment="Right" Height="20"  Width="80"
 CommandParameter="{Binding PersonModelProp}" 
 Command="{Binding EditPersonCommand}" />

另外，看到的此处和这里 。

Also, see here and here.

修改

要确保你的事件被提出正确的，你应该提高CanExecuteChanged事件时， PersonModelProp 价值变动

To ensure that your events are being raised properly you should raise the CanExecuteChanged event when the PersonModelProp value changes.

命令：

public class EditPersonCommand : ICommand
{
  public bool CanExecute(object parameter)
  {
     PersonModel p = parameter as PersonModel;
     return p != null && p.Age > 0;
  }

  public event EventHandler CanExecuteChanged;

  public void Execute(object parameter) 
  {
      //command implementation
  }

  public void RaiseCanExecuteChanged()
  {
      var handler = CanExecuteChanged;
      if(handler != null)
      {
          handler(this, EventArgs.Empty);
      }
  }
}

和视图模型：

public class PersonViewModel : ViewModelBase
{
  private PersonModel _PersonModel;
  private EditPersonCommand _EditPersonCommand;

  ///<remarks>
  /// must use the parameterless constructor to satisfy <Window.Resources>
  ///</remarks>
  public PersonViewModel()
     : this(new PersonModel())
  {
      _EditPersonCommand = new EditPersonCommand();
  }

  public PersonViewModel(PersonModel personModel)
  {
     _PersonModel = personModel;
  }

  public ICommand EditPersonCommand
  {
     get
     {
         return _EditPersonCommand;
     }
  }

  public PersonModel PersonModelProp
  {
      get
      {
         return _PersonModel;
      }
      set
      {
         _PersonModel = value;
         OnPropertyChanged("PersonModelProp");
         EditPersonCommand.RaiseCanExecuteChanged();
      }
    }
}

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