Question

我是MVVM模式的新手。我在更新文本块时遇到问题。我有一个文本块和菜单按钮。

//View.xaml for textblock

<Grid DataContext="{Binding Source={StaticResource MenuHandler}}" Height="23" HorizontalAlignment="Stretch" VerticalAlignment="Top"  Grid.Row="2" Grid.ColumnSpan="3" Margin="5,0,5,0" >                                   
     <Grid.ColumnDefinitions>
         <ColumnDefinition Width="*" />
         <ColumnDefinition Width="200" />
      </Grid.ColumnDefinitions>    
      <TextBlock Text="{Binding Path=StatusText, UpdateSourceTrigger=PropertyChanged}" Name="StatusText" Grid.Column="0" HorizontalAlignment="Left" VerticalAlignment="Stretch" Width="100" IsEnabled="True" Height="23"/>                
</Grid>

 //View.xaml for Menu 

<Menu DataContext="{Binding Source={StaticResource MenuHandler}}" Height="25" HorizontalAlignment="Stretch"  Name="menu1" VerticalAlignment="Top" Visibility="Visible" Background="AliceBlue">    
  <MenuItem Header="_New" Command="{Binding NewFileCommand}" Name="NewFile"  >
       <MenuItem.Icon>
           <Image Source="/WhitelistBlacklistEditor;component/Images/NewFile.png"  Width="25"/>
       </MenuItem.Icon>
  </MenuItem>
</Menu >

在视图模型中，我正在使用MenuHandler类

// MenuHandler.cs

public string StatusText
{
    get { return _StatusText; }
    set
    {
       _StatusText = value;
        RaisePropertyChangedEvent(StatusText);
     }
}

public ICommand NewFileCommand
{
    get { return new DelegateCommand(NewFile_Click); }
}

public void NewFile_Click()
{
    StatusText = "checking";
}

如果我在NewFile_Click（）方法之外更新StatusText，则值在文本块中更新，但如果我在NewFile_Click（）中通过ICommand执行相同操作，则它不会更新。我也通过INotifyPropertyChanged继承了MenuHandler类，并通过在xaml中添加twoway模式进行检查。

Answer 1

public class DelegateCommand : ICommand

{

private readonly Predicate _canExecute; private readonly Action _execute;

public event Event Handler CanExecuteChanged;

public Delegate Command(Action<object> execute) 
               : this(execute, null)
{
}

public Delegate Command(Action<object> execute, 
               Predicate<object> canExecute)
{
    _execute = execute;
    _canExecute = canExecute;
}

public override bool CanExecute(object parameter)
{
    if (_canExecute == null)
    {
        return true;
    }

    return _canExecute(parameter);
}

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

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

}

private DelegateCommand _NewFileCommand;
    public ICommand NewFileCommand
    {
        get
        {
            if (adcom == null)
                adcom = new DelegateCommand(CommandExecuter, CommandExecute);
            return adcom;
        }

    }

    private bool CommandExecuter(object obj)
    {
        return true;
    }
    private void CommandExecute(object obj)
    {
            Statuscheck="";
    }

如何通过NewFile菜单单击命令更新文本块

1 个答案: