WPF：条件绑定

Question

If my CheckBox is checked, I would like to disable the ComboBox and select "Yes". This works, what I would like to do is make this conditional such that when I uncheck the CheckBox MyBooleanProperty is not updated and "Yes" is still selected. The ComboBox itself should enable allowing me to choose "No" if desired.

<CheckBox Name="chkDefault" IsChecked="{Binding MyBooleanProperty, Mode=OneWayToSource}" />
<ComboBox IsEnabled="{Binding IsChecked, ElementName=chkDefault, Converter={StaticResource InverseBooleanConverter}}">
    <ComboBoxItem Content="No" />
    <ComboBoxItem Content="Yes" IsSelected="{Binding MyBooleanProperty}" />
</ComboBox>

In the past, I've done this with multiple properties(see below) but I'm wondering if there isn't something simpler than can be done in XAML that I am not aware of.

The View...

<CheckBox IsChecked="{Binding MyBooleanProperty, Mode=OneWayToSource}" />
<ComboBox IsEnabled="{Binding MyBooleanProperty, Converter={StaticResource InverseBooleanConverter}}">
    <ComboBoxItem Content="No" />
    <ComboBoxItem Content="Yes" IsSelected="{Binding MyOtherBooleanProperty}" />
</ComboBox>

And the ViewModel...

public bool MyBooleanProperty
{
    get { return _myBooleanProperty; }
    set
    {
        if (_myBooleanProperty != value)
        {
             _myBooleanProperty = value;

             if (_myBooleanProperty)
                MyOtherBooleanProperty = true;

             base.OnPropertyChanged("MyBooleanProperty");
        }
    }
}

public bool MyOtherBooleanProperty
{
    get { return _myOtherBooleanProperty; }
    set
    {
        if (_myOtherBooleanProperty != value)
        {
             _myOtherBooleanProperty = value;

             base.OnPropertyChanged("MyOtherBooleanProperty");
        }
    }
}

Answer 1

You are describing the logic you would like your view to have. To me, at least, that generally means that such logic belongs in the view model.

But, I would not do the bindings the way you have. I would use something like this:

<CheckBox Name="chkDefault" IsChecked="{Binding UseDefault}" />
<ComboBox IsEnabled="{Binding EnableComboBox}}" SelectedItem="{Binding SelectedComboItem}">
    <ComboBoxItem Content="No" />
    <ComboBoxItem Content="Yes" />
</ComboBox>

Then in your view model, you have UseDefault , EnableComboBox , and SelectedComboItem properties which clearly state what the behavior should be.

Also, by doing this in the view model, you are making the behavior unit testable. :)

Answer 2

I would control the logic for this in the viewmodel, and not try to imply the logic via bindings. The View should just care that you've bound the combobox selection to a backing data member (two-way), and that the checkbox's value is bound too.

    public bool IsOverrideProperty
    {
        get { return _IsOverrideProperty; }
        set
        {
            if (_IsOverrideProperty != value)
            {
                _IsOverrideProperty = value;

                if (_IsOverrideProperty)
                    Selection = Options[0];

                base.OnPropertyChanged("IsOverrideProperty");
            }
        }
    }

    bool _IsOverrideProperty;

    public string Selection
    {
        get { return _Selection; }
        set
        {
            if (_Selection != value)
            {
                _Selection = value;

                base.OnPropertyChanged("Selection");
            }
        }
    }

    string _Selection;

    public string[] Options = new[] { "Yes", "No" };

The View:

<CheckBox IsChecked="{Binding IsOverrideProperty}" />
<ComboBox IsEnabled="{Binding IsOverrideProperty, Converter={StaticResource InverseBooleanConverter}}"
          SelectedValue="{Binding Selection}" ItemsSource="{Binding Options}">
</ComboBox>

Options could be in an observablecollection, but this probably works okay.