[原创]Prism Command 和 IsEnabled 的冲突解决方法

在开发Silverlight项目中,学习使用MVVM ，在Button的click上想使用Prism下的Click Command方法来处理Click事件，发现当用到Click事件绑定的时候，
绑定IsEnabled的属性不起作用了。
XAML代码如下

      <Button Height="36" HorizontalAlignment="Left" Margin="128,126,0,0" VerticalAlignment="Top" Width="58" Content="New" 
         Visibility="{Binding IsNewVisible, Converter={StaticResource BooleanToVisibilityConverter}, Mode=OneWay}"
         IsEnabled="{Binding IsNewEnabled, Mode=OneWay}"   commands:Click.Command="{Binding BTNClickCommand}"
            />
      <Button Height="36" Margin="292,126,273,0" VerticalAlignment="Top" Content="Enabled" commands:Click.Command="{Binding BTNEnabledCommand}"/>

C#代码如下

    public class MainPageViewModel : INotifyPropertyChanged  
    {
        public MainPageViewModel()
        {
            BTNEnabledCommand = new DelegateCommand<object>(OnEnabledCommand);
            BTNClickCommand = new DelegateCommand<object>(OnClickCommand);
        }
        private void OnEnabledCommand(object arg)
        {
            IsNewEnabled = !IsNewEnabled;                        
        }
        private void OnClickCommand(object arg)
        {
            MessageBox.Show("Hello Wingfay");
        }
        public ICommand BTNClickCommand { get; private set; }
        public ICommand BTNEnabledCommand { get; private set; }
        private bool _IsNewEnabled;
        public bool IsNewEnabled
        {
            get
            {
                return _IsNewEnabled;
            }
            set
            {
                _IsNewEnabled = value;
                OnPropertyChanged("IsNewEnabled");
            }
        }
       ....
    }

郁闷死我了，在网上找资料发现了这个

引用

The Click.Command attached property provided by Composite Application Guidance for WPF & Silverlight requires you to specify an ICommand (generally using DelegateCommand class). In that command you define an Execute and CanExecute method. The CAL relies on this latter method to check if the command can be executed and sets the control's IsEnabled property to the value returned by the CanExecute method.

So, when you use CAL's Click attached property to define commands, the IsEnabled property is set at runtime by the command behavior (more precisely in the UpdateEnabledState method of the CommandBehaviorBase class) which is executed after the isEnabled set in XAML.

 

      protected virtual void UpdateEnabledState()

      {

            ...

            if (this.Command != null)

            {

                TargetObject.IsEnabled = this.Command.CanExecute(this.CommandParameter);

            }
      }

 

You can use the RaiseCanExecuteChanged method from the DelegateCommand class to reevalute the CanExecute method and that will update the isEnabled property of all attached controls.

以上是Prism开发人员的回答
然后看了下Prism关于Command的源代码 终于明白了点
该后的代码如下
XAML

    <UserControl.Resources>
        <Local:BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
        <Local:MainPageViewModel x:Key="MainPageViewModelDataSource" d:IsDataSource="True"/>
 
    </UserControl.Resources>  
    
<Grid x:Name="LayoutRoot" DataContext="{Binding Source={StaticResource MainPageViewModelDataSource}}">
      <Button Height="36" HorizontalAlignment="Left" Margin="128,126,0,0" VerticalAlignment="Top" Width="58" Content="New" 
         Visibility="{Binding IsNewVisible, Converter={StaticResource BooleanToVisibilityConverter}, Mode=OneWay}"
           commands:Click.Command="{Binding BTNClickCommand}"
            />
      <Button Height="36" Margin="292,126,273,0" VerticalAlignment="Top" Content="Enabled" commands:Click.Command="{Binding BTNEnabledCommand}"/>


  </Grid>

C#代码

        public MainPageViewModel()
        {
            BTNEnabledCommand = new DelegateCommand<object>(OnEnabledCommand);
            BTNClickCommand = new DelegateCommand<object>(OnClickCommand, e => IsNewEnabled);

        }


        private void OnEnabledCommand(object arg)
        {
            IsNewEnabled = !IsNewEnabled;
        }


        private void OnClickCommand(object arg)
        {
            MessageBox.Show("Hello Wingfay");
        }


        private bool _IsNewEnabled;
        public bool IsNewEnabled
        {
            get
            {
                return _IsNewEnabled;
            }
            set
            {
                _IsNewEnabled = value;
                ((DelegateCommand<object>)BTNClickCommand).RaiseCanExecuteChanged();
            }
        }

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