c# - 为什么更改 DataGrid ComboBox 值根本不会更新绑定(bind)属性？

Question

我有 DataGridComboBoxColumn 应该显示整数或文本“默认”。当我添加行时，组合框从 viewmodel 的绑定(bind)属性中获取正确的值，但是当我在用户界面中更改值时，不会调用该属性的集合。我尝试了 SelectedValueBinding 和 SelectedItemBinding。转换器的 ConvertBack 永远不会被调用。我不知道应该调用它。

有效的东西:

DataGrid SelectedItem 绑定(bind)

文本列双向绑定(bind)(此处省略)

这是我的代码:

XAML:

<DataGrid Name="SelectionSetsGrid" CanUserAddRows="False" CanUserResizeColumns="True" CanUserSortColumns="True" 
                      ItemsSource="{Binding SelectionSets}" AutoGenerateColumns="False"
                      SelectedItem="{Binding SelectedSelectionSet}">
 <DataGrid.Columns>
  <DataGridComboBoxColumn Header="Width" SelectedValueBinding="{Binding LineWidthIndex}">
    <DataGridComboBoxColumn.ElementStyle>
        <Style TargetType="ComboBox" BasedOn="{StaticResource Theme.ComboBox.Style}">
            <Setter Property="ItemsSource" Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.LineWidths}"/>
            <Setter Property="IsReadOnly" Value="True"/>
            <Setter Property="ItemTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <WrapPanel>
                            <TextBlock Text="{Binding Converter={StaticResource IntToIntTextOrDefaultConverter}}" VerticalAlignment="Center"/>
                        </WrapPanel>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DataGridComboBoxColumn.ElementStyle>
    <DataGridComboBoxColumn.EditingElementStyle>
        <Style TargetType="ComboBox" BasedOn="{StaticResource Theme.ComboBox.Style}">
            <Setter Property="ItemsSource" Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.LineWidths}"/>
            <Setter Property="ItemTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <WrapPanel>
                            <TextBlock Text="{Binding Converter={StaticResource IntToIntTextOrDefaultConverter}}" VerticalAlignment="Center"/>
                        </WrapPanel>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DataGridComboBoxColumn.EditingElementStyle>
  </DataGridComboBoxColumn>
 </DataGrid.Columns>
</DataGrid>

ViewModel(ViewModel 实现 INotifyPropertyChanged 和 SetValue 引发 PropertyChanged):

public class SelectedObjectsViewModel : ViewModel
{
    private int[] _lineWidths = { -1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    public ObservableCollection<int> LineWidths { get; private set; };

    private ObservableCollection<SelectionSetViewModel> _selectionSets;
    public ObservableCollection<SelectionSetViewModel> SelectionSets
    {
        get { return _selectionSets; }
        set { this.SetValue(ref _selectionSets, value); }
    }

    private SelectionSetViewModel _selectedSelectionSet;
    public SelectionSetViewModel SelectedSelectionSet
    {
        get { return this._selectedSelectionSet; }
        set { this.SetValue(ref _selectedSelectionSet, value); }
    }
}

DataGrid 行的 ViewModel(ViewModel 实现 INotifyPropertyChanged 和 SetValue 引发 PropertyChanged):

public class SelectionSetViewModel : ViewModel
{
    public SelectionSetViewModel()
    {
        LineWidthIndex = -1;
    }
    private int _lineWidthIndex;
    public int LineWidthIndex
    {
        get { return _lineWidthIndex; }
        set { SetValue(ref _lineWidthIndex, value); }
    }

转换器:

public class IntToIntTextOrDefaultConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        if ((int)value == -1)
            return Fusion.App.Current.Resources["StrDefault"].ToString();

        return value.ToString();
    }

    public object ConvertBack(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        return value.Equals(true) ? parameter : Binding.DoNothing;
    }
}

Answer 1

似乎在某些情况下，例如在编辑文本列并按 enter 或添加新行之后，属性实际上在更改组合框值后更新(设置调用)。所以我只是将 UpdateSourceTrigger=PropertyChanged 添加到绑定(bind)中，并且对源属性的更新立即发生(而不是在一些随机操作之后)。请注意，从 ComboBox 更改焦点不足以更新源属性，所以我认为它从未更新。

<DataGrid Name="SelectionSetsGrid" CanUserAddRows="False" CanUserResizeColumns="True" CanUserSortColumns="True" 
              ItemsSource="{Binding SelectionSets}" AutoGenerateColumns="False"
              SelectedItem="{Binding SelectedSelectionSet}">
        <DataGridComboBoxColumn Header="{StaticResource XpStrTopologyWidth}" SelectedItemBinding="{Binding LineWidthIndex, UpdateSourceTrigger=PropertyChanged}">
            <DataGridComboBoxColumn.ElementStyle>
                <Style TargetType="ComboBox" BasedOn="{StaticResource Theme.ComboBox.Style}">
                    <Setter Property="ItemsSource" Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.LineWidths}"/>
                    <Setter Property="IsReadOnly" Value="True"/>
                    <Setter Property="ItemTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <WrapPanel>
                                    <TextBlock Text="{Binding Converter={StaticResource IntToIntTextOrDefaultConverter}}" VerticalAlignment="Center"/>
                                </WrapPanel>
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </DataGridComboBoxColumn.ElementStyle>
            <DataGridComboBoxColumn.EditingElementStyle>
                <Style TargetType="ComboBox" BasedOn="{StaticResource Theme.ComboBox.Style}">
                    <Setter Property="ItemsSource" Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.LineWidths}"/>
                    <Setter Property="ItemTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <WrapPanel>
                                    <TextBlock Text="{Binding Converter={StaticResource IntToIntTextOrDefaultConverter}}" VerticalAlignment="Center"/>
                                </WrapPanel>
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </DataGridComboBoxColumn.EditingElementStyle>
        </DataGridComboBoxColumn>                        
    </DataGrid.Columns>
</DataGrid>