WPF：仅选择一个单元格时显示上下文菜单

Question

What is wrong with this code?

The DataTrigger on SelectedCells.Count is not firing up.

<DataGrid.RowStyle>
    <Style TargetType="DataGridRow">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Exclude.Exclude,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Value="True">
                <Setter Property="Background" Value="#FFEBEBEB"/>
            </DataTrigger>
            <DataTrigger Binding="{Binding Path=SelectedCells.Count,ElementName=dgAssets }" Value="1">
                <Setter Property="ContextMenu" Value="{StaticResource RowMenu}" />
                <Setter Property="Background" Value="Green"/>
            </DataTrigger>
        </Style.Triggers>                          
    </Style>
</DataGrid.RowStyle>

Trying to show the context menu , only when just a single cell is selected.

Answer 1

The SelectedCells property of a DataGrid returns an internal object called SelectedCellsCollection . It extends another class called VirtualizedCellInfoCollection . It does not implement neither INotifyCollectionChanged nor INotifyPropertyChanged interfaces. Moreover its Count property is not a dependecy property.

So your binding is not able to notify to your data trigger when the number of selected cells increases or decreases. For the data trigger its value is always 0.