WPF ItemsControl MultiConverter

Question

所以，我有一个ItemsControl绑定到ObservableCollection中的Items集合....作为DataTemplate的一部分，我有两个按钮，其中一个是将ItemsControl ItemsSource传递给一个多转换器....

这是问题....当我向CurrentTransaction.Items添加一个项目时，转换器，GetPriceMultiConverter，被调用就好了但是当我从CurrentTransaction.Items中删除一个项目时，GetPriceMultiConverter没有触发但是UI正在更新...

这是XAML

<ItemsControl x:Name="SalesScreen" ItemsSource="{Binding CurrentTransaction.Items}" >
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <Button Width="225" Background="Transparent" Foreground="White" Margin=".5" Content="{Binding DisplayName}" Command="{Binding DataContext.RemoveSaleCommand, ElementName=Screen}" CommandParameter="{Binding}" />
                <Button Width="90" Background="Transparent" Foreground="White" Margin=".5" Command="{Binding DataContext.RemoveSaleCommand, ElementName=Screen}" CommandParameter="{Binding}" >
                    <Button.Content>
                        <MultiBinding Converter="{StaticResource GetPriceMultiConverter}" >
                            <Binding ></Binding>
                            <Binding ElementName="SalesScreen" Path="ItemsSource" ></Binding>
                        </MultiBinding>
                    </Button.Content>
                </Button>
            </StackPanel>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

这是绑定属性

    private Transaction _CurrentTransaction;
    public Transaction CurrentTransaction
    {
        get { return _CurrentTransaction; }
        set { _CurrentTransaction = value; OnPropertyChanged("CurrentTransaction"); }
    }

有什么想法吗？