折叠所有展开器并默认展开其中一个展开器

Question

我有多个扩展器,我正在寻找一种方法来折叠所有其他扩展器,当其中一个扩展时.我在这里找到了这个解决方案

XAML:

<StackPanel Name="StackPanel1">
    <StackPanel.Resources>
        <local:ExpanderToBooleanConverter x:Key="ExpanderToBooleanConverter" />
    </StackPanel.Resources>
    <Expander Header="Expander 1"
        IsExpanded="{Binding SelectedExpander, Mode=TwoWay, Converter={StaticResource ExpanderToBooleanConverter}, ConverterParameter=1}">
        <TextBlock>Expander 1</TextBlock>
    </Expander>
    <Expander Header="Expander 2"
        IsExpanded="{Binding SelectedExpander, Mode=TwoWay, Converter={StaticResource ExpanderToBooleanConverter}, ConverterParameter=2}">
        <TextBlock>Expander 2</TextBlock>
    </Expander>
    <Expander Header="Expander 3"
        IsExpanded="{Binding SelectedExpander, Mode=TwoWay, Converter={StaticResource ExpanderToBooleanConverter}, ConverterParameter=3}">
        <TextBlock>Expander 3</TextBlock>
    </Expander>
    <Expander Header="Expander 4"
        IsExpanded="{Binding SelectedExpander, Mode=TwoWay, Converter={StaticResource ExpanderToBooleanConverter}, ConverterParameter=4}">
        <TextBlock>Expander 4</TextBlock>
    </Expander>
</StackPanel>

转换器:

public class ExpanderToBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (value == parameter);

        // I tried thoses too :
        return value != null && (value.ToString() == parameter.ToString());
        return value != null && (value.ToString().Equals(parameter.ToString()));
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return System.Convert.ToBoolean(value) ? parameter : null;
    }
}

视图模型:

public class ExpanderListViewModel : INotifyPropertyChanged
{
    private Object _selectedExpander;

    public Object SelectedExpander
    {
        get { return _selectedExpander; } 
        set
        {
            if (_selectedExpander == value)
            {
                return;
            }

            _selectedExpander = value;
            OnPropertyChanged("SelectedExpander");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

初始化

var viewModel = new ExpanderListViewModel();
StackPanel1.DataContext = viewModel;
viewModel.SelectedExpander = 1;

// I tried this also
viewModel.SelectedExpander = "1";

---

它工作正常,但现在我想在应用程序启动时扩展其中一个扩展器!

我已经尝试将值(1,2或3)放在SelectedExpander属性中,但默认情况下没有扩展器扩展!

如何将这种可能性添加到我的扩展器中？

Answer 1

考虑如果在Expander 2上选择Expander 1时调用UpdateSource会发生什么:

• ConvertBack使用当前IsExpanded值(false)调用Expander 2 ,然后返回null.
• SelectedExpander已更新为null.
• Convert为所有其他扩展器调用,因为已SelectedExpander更改,导致所有其他IsExpanded值也被设置false为.

当然,这不是正确的行为.所以解决方案依赖于源永远不会被更新,除非用户实际切换扩展器.

因此,我怀疑问题是控件的初始化以某种方式触发源更新.即使扩展器1被正确初始化为扩展,当在任何其他扩展器上刷新绑定时,它也会被重置.

为了使ConvertBack正确的,那就需要了解其他扩展的:它应该只返回null,如果所有的人都崩溃了.但是,我没有看到从转换器中处理这个问题的干净方法.也许最好的解决方案是使用单向绑定(否ConvertBack)并以这种方式或类似方式处理Expanded和Collapsed事件(其中_expanders是所有扩展器控件的列表):

private void OnExpanderIsExpandedChanged(object sender, RoutedEventArgs e) {
    var selectedExpander = _expanders.FirstOrDefault(e => e.IsExpanded);
    if (selectedExpander == null) {
        viewmodel.SelectedExpander = null;
    } else {
        viewmodel.SelectedExpander = selectedExpander.Tag;
    }
}

在这种情况下,我使用Tag作为viewmodel中使用的标识符.

编辑:

要以更"MVVM"的方式解决它,您可以为每个扩展器设置一组视图模型,并使用要绑定的单个属性IsExpanded:

public class ExpanderViewModel {
    public bool IsSelected { get; set; }
    // todo INotifyPropertyChanged etc.
}

存储集合ExpanderListViewModel并在初始化时为每个处理程序添加PropertyChanged处理程序:

// in ExpanderListViewModel
foreach (var expanderViewModel in Expanders) {
    expanderViewModel.PropertyChanged += Expander_PropertyChanged;
}

...

private void Expander_PropertyChanged(object sender, PropertyChangedEventArgs e) {
    var thisExpander = (ExpanderViewModel)sender;
    if (e.PropertyName == "IsSelected") {
        if (thisExpander.IsSelected) {
            foreach (var otherExpander in Expanders.Except(new[] {thisExpander})) {
                otherExpander.IsSelected = false;
            }
        }
    }
}

然后将每个扩展器绑定到Expanders集合的不同项:

<Expander Header="Expander 1" IsExpanded="{Binding Expanders[0].IsSelected}">
    <TextBlock>Expander 1</TextBlock>
</Expander>
<Expander Header="Expander 2" IsExpanded="{Binding Expanders[1].IsSelected}">
    <TextBlock>Expander 2</TextBlock>
</Expander>

(您可能还希望研究定义自定义ItemsControl以根据集合动态生成扩展器.)

在这种情况下,SelectedExpander将不再需要该属性,但可以通过以下方式实现:

private ExpanderViewModel _selectedExpander;
public ExpanderViewModel SelectedExpander
{
    get { return _selectedExpander; } 
    set
    {
        if (_selectedExpander == value)
        {
            return;
        }

        // deselect old expander
        if (_selectedExpander != null) {
           _selectedExpander.IsSelected = false;
        }

        _selectedExpander = value;

        // select new expander
        if (_selectedExpander != null) {
            _selectedExpander.IsSelected = true;
        }

        OnPropertyChanged("SelectedExpander");
    }
}

并将以上PropertyChanged处理程序更新为:

if (thisExpander.IsSelected) {
    ...
    SelectedExpander = thisExpander;
} else {
    SelectedExpander = null;
}

所以现在这两行是初始化第一个扩展器的等效方法:

viewModel.SelectedExpander = viewModel.Expanders[0];
viewModel.Expanders[0].IsSelected = true;