C＃WPF Listview项目刷新在OnPropertyChanged之后不触发

Question

I created a view control to display data graphically. As there could be number of instances of the view, I used a ListView control and bound it to an observable collection of objects - Sheets. Sheets is an observable collection of SheetContainer object which has sheet and a name. The viewer displays sheet.

The xaml for the listview looks like:

<ListView x:Name="ListViewSheetSlider" Height="170" Grid.Row="1" BorderThickness="0" 
                              ItemsSource="{Binding Sheets}" SelectionChanged="ListViewSheetSlider_SelectionChanged" >
    <ListView.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Vertical">
                <TextBlock Text="{Binding Name}" />
                <Viewbox Width="150" Height="150">
                    <SheetViewer:Viewer SetSheet="{Binding MySheet, NotifyOnSourceUpdated=True}" />
                </Viewbox>
            </StackPanel>
        </DataTemplate>
    </ListView.ItemTemplate>
    <ListView.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Horizontal"></StackPanel>
        </ItemsPanelTemplate>
    </ListView.ItemsPanel>
</ListView>

The SelectionChanged method looks like:

private void UpdateSheetAndSlider()
{
    workspace.Sheets[SelectedSheetIndex] = MySheetDesigner.Sheet;
    //   ((SheetContainer)ListViewSheetSlider.SelectedItem).MySheet = MySheetDesigner.Sheet;
    Sheets[SelectedSheetIndex].MySheet = MySheetDesigner.Sheet;
}


private void MySheetDesigner_SheetChanged(object sender, EventArgs e)
{
    UpdateSheetAndSlider();
}

private void ListViewSheetSlider_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    int index = ListViewSheetSlider.SelectedIndex;

    UpdateSheetAndSlider();
    SelectedSheetIndex = index;
    MySheetDesigner.Sheet = workspace.Sheets[index];
    ListViewSheetSlider.UpdateLayout();
}

The SheetContainer implementation is simple. It looks like:

public class SheetContainer : INotifyPropertyChanged
{
    public string Name { get; set; }

    private Sheet mySheet;
    public Sheet MySheet
    {
        get => mySheet;
        set
        {
            mySheet = value;

            OnPropertyChanged("MySheet");
        }
    }

    #region INotifyPropertyChanged Handler
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
    #endregion

}

The viewer xaml and codebehind look like:

<UserControl x:Class="SheetViewer.Viewer"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:SheetViewer"
             xmlns:cad="clr-namespace:Cad;assembly=Cad"
             mc:Ignorable="d"        
             d:DesignHeight="450" d:DesignWidth="800">
    <Grid>
        <cad:Cad
            x:Name="CadSurface" >
        </cad:Cad>
    </Grid>
</UserControl>

code behind:

public partial class Viewer : UserControl
{

    public static readonly DependencyProperty SetSheetProperty =
             DependencyProperty.Register("SetSheet", typeof(Sheet), typeof(Viewer), new
                PropertyMetadata(default(Sheet), new PropertyChangedCallback(OnSetSheetChanged)));

    public Sheet SetSheet
    {
        get { return (Sheet)GetValue(SetSheetProperty); }
        set { SetValue(SetSheetProperty, value);}
    }

    private static void OnSetSheetChanged(DependencyObject d,
       DependencyPropertyChangedEventArgs e)
    {
        Viewer UserControl1Control = d as Viewer;
        UserControl1Control.OnSetSheetChanged(e);
    }

    private void OnSetSheetChanged(DependencyPropertyChangedEventArgs e)
    {
        //tbTest.Text = e.NewValue.ToString();
        Sheet s = (Sheet)e.NewValue;
        DrawSheet(s);
    }

    public Viewer()
    {
        InitializeComponent();
    }


    private void DrawSheet(Sheet sheet)
    {
        CadSurface.Draw();
    }

}

I expect the DrawSheet method to fire upon selection change in the listview. The property changed does get fired in SheetContainer, but does not propagate further to draw the sheet. Please note that when the listview is populated, the methods are called properly and the initial views are drawn.

I have spent substantial amount of time but somehow am missing the key ingredient. Could anyone please help?

Thanks

Answer 1

When the instance that is assigned to SetSheet is the same, then the DependencyPropertyChanged event won't trigger. This would explain it all. The point is the DependencyProperty checks old and new value for equality before setting the value. If they are equal no change will be propagated.