防止 MVVM/MDI 应用程序中出现几乎重复的 RelayCommands

发布于 2025-01-04 17:09:15 字数 1133 浏览 2 评论 0原文

我正在使用 MDI 解决方案（请参阅 http://wpfmdi.codeplex.com/）和 MVVM。

我使用一个 RelayCommand 将工具栏和/或菜单绑定到主 ViewModel，例如：

 ICommand _editSelectedItemCommand;
    public ICommand EditSelectedItemCommand
    {
        get
        {
            return _editSelectedItemCommand ?? (_editSelectedItemCommand = new RelayCommand(param => CurrentChildViewModel.EditSelectedItem(),
                param => ((CurrentChildViewModel != null) && (CurrentChildViewModel.CanExecuteEditSelectedItem))));
        }
    }

但是，在子窗口中，要将按钮绑定到相同的功能，我需要另一个 RelayCommand，它几乎相同，只是它调用方法 EditSelectedItem 和 CanExecuteEditSelectedItem直接地。它看起来像：

 ICommand _editSelectedItemCommand;
    public ICommand EditSelectedItemCommand
    {
        get
        {
            return _editSelectedItemCommand ?? (_editSelectedItemCommand = new RelayCommand(param => EditSelectedItem(),
                param => CanExecuteEditSelectedItem))));
        }
    }

我需要大约 10 个，将来可能需要 50 个或更多这样的命令，所以我喜欢现在就以正确的方式执行。有没有办法防止这种情况或有更好的方法来做到这一点？

原文

I'm using an MDI solution (see http://wpfmdi.codeplex.com/) and MVVM.

I use one RelayCommand to bind the toolbar and/or menu to the Main ViewModel, like:

 ICommand _editSelectedItemCommand;
    public ICommand EditSelectedItemCommand
    {
        get
        {
            return _editSelectedItemCommand ?? (_editSelectedItemCommand = new RelayCommand(param => CurrentChildViewModel.EditSelectedItem(),
                param => ((CurrentChildViewModel != null) && (CurrentChildViewModel.CanExecuteEditSelectedItem))));
        }
    }

However, in the child window, to bind a button to the same functionality I need another RelayCommand which is almost equal except it calls the methods EditSelectedItem and CanExecuteEditSelectedItem directly. It would look like:

 ICommand _editSelectedItemCommand;
    public ICommand EditSelectedItemCommand
    {
        get
        {
            return _editSelectedItemCommand ?? (_editSelectedItemCommand = new RelayCommand(param => EditSelectedItem(),
                param => CanExecuteEditSelectedItem))));
        }
    }

I need about 10 and in the future maybe 50 or more of such commands so I like to do it the right way now.
Is there a way to prevent this or a better way to do this?

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秋千易 2025-01-11 17:09:15

您可以从主视图模型中删除第一个命令，因为子视图模型中的命令已经足够了。

只需在 xaml 标记中使用这样的绑定即可：

<Button Command="{Binding CurrentChildViewModel.EditSelectedItemCommand}" 
        Content="Button for the main view model" />

另外，如果我正确理解您的代码，它规定如果 CurrentChildViewModel 属性为 null，则该命令将被禁用。
如果您需要这样的行为，您应该将此转换器添加到您的代码中并稍微重写绑定：

public class NullToBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value != null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

XAML：

<Application.Resources>
    <local:NullToBooleanConverter x:Key="NullToBooleanConverter" />
</Application.Resources>
<!-- your control -->
<Button Command="{Binding CurrentChildViewModel.EditSelectedItemCommand}" 
        IsEnabled="{Binding CurrentChildViewModel, Converter={StaticResource NullToBooleanConverter}}" />

You can remove the first command from the main viewmodel, because the command in the child viewmodel is more than enough.

Just use the binding like this in the xaml markup:

<Button Command="{Binding CurrentChildViewModel.EditSelectedItemCommand}" 
        Content="Button for the main view model" />

Also if I understand your code correctly, it has the stipulation that if the CurrentChildViewModel property is null than the command will be disabled.
If you need such behavior, you should add this converter to your code and slightly rewrite the binding:

public class NullToBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value != null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

XAML:

<Application.Resources>
    <local:NullToBooleanConverter x:Key="NullToBooleanConverter" />
</Application.Resources>
<!-- your control -->
<Button Command="{Binding CurrentChildViewModel.EditSelectedItemCommand}" 
        IsEnabled="{Binding CurrentChildViewModel, Converter={StaticResource NullToBooleanConverter}}" />

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