項目模板內的用戶控件的WPF更改通知不起作用

Question

我試圖將ObservableCollection<FilterControlViewmodel>中的每個視圖模型作為DataContext到ItemsControl的用戶控件FilterControl 。

綁定本身可以正常工作。 從FilterControlViewmodel.FilterName正確顯示了"InitialFilterName" ，但是該屬性的任何更新都不會通知UI。

另外，向ObservableCollection<FilterControlViewmodel>添加元素也可以找到並添加其他用戶控件。 但是同樣， FilterControlViewmodel內部的值不會更新到UI。

任何有關缺少通知的提示都將不勝感激。 謝謝。

MainWindow.xaml

<Window.DataContext>
   <local:MainWindowViewmodel/>
</Window.DataContext>

<Grid>
   <ItemsControl ItemsSource="{Binding FilterViewmodel.FilterControls}">
      <ItemsControl.ItemTemplate>
          <DataTemplate>
             <filter:FilterControl DataContext="{Binding}"></filter:FilterControl>
          </DataTemplate>
       </ItemsControl.ItemTemplate>
  </ItemsControl>
</Grid>

FilterControl.xaml

<UserControl.DataContext>
   <local:FilterControlViewmodel/>
</UserControl.DataContext>

<Grid>
   <Label Grid.Column="0" Grid.Row="0" Content="{Binding FilterName}"></Label>
   <ComboBox Grid.Column="0" Grid.Row="1" ItemsSource="{Binding FilterValues}" SelectedItem="{Binding FilterValueSelected}"></ComboBox>
   <Button Grid.Column="1" Grid.Row="1" Content="X" Command="{Binding ResetFilterCommand}"></Button>
</Grid>

MainWindowViewmodel.cs

public class MainWindowViewmodel : INotifyPropertyChanged
{
   public FilterViewmodel FilterViewmodel
        {
            get => _filterViewmodel;
            set
            {
                if (Equals(value, _filterViewmodel)) return;
                _filterViewmodel = value;
                OnPropertyChanged();
            }
        }

FilterViewmodel.cs

public class FilterViewmodel : INotifyPropertyChanged
{
  public ObservableCollection<FilterControlViewmodel> FilterControls
        {
            get => return _filterControls;
            set
            {
                if (Equals(value, _filterControls)) return;
                _filterControls = value;
                OnPropertyChanged();
            }
        }

FilterControlViewmodel.cs

public class FilterControlViewmodel : INotifyPropertyChanged
{
   private string _filterName = "InitialFilterName";
   public string FilterName
   {
      get => _filterName;
      set
      {
         if (value == _filterName) return;
         _filterName = value;
         OnPropertyChanged();
      }
   }

Answer 1

您應刪除以下標記，因為它會創建FilterControlViewmodel另一個實例：

<UserControl.DataContext>
   <local:FilterControlViewmodel/>
</UserControl.DataContext>

然后， FilterControl將從ItemsControl的當前項目（ FilterControlViewmodel ）繼承其DataContext ，而無需顯式設置DataContext屬性：

<ItemsControl ItemsSource="{Binding FilterViewmodel.FilterControls}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <filter:FilterControl/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>