Visual Studio无法识别WPF中数据绑定的正确类型

Question

Here is a small example that i created to illustrate my problem.

public class DataItem
{
    public DataItem() {}
    public DataItem(bool isSelected)
    {
        IsSelected = isSelected;
    }

    public bool IsSelected { get; set; }
}


public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        Items = new ObservableCollection<DataItem> {new DataItem(true), new DataItem()};
    }

    public ObservableCollection<DataItem> Items { get; set; }
}

The XAML is:

<Window x:Class="RoomDesigner.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:ignore="http://www.ignore.com"
        xmlns:viewModel="clr-namespace:RoomDesigner.ViewModel"
        mc:Ignorable="d ignore"
        Height="350"
        Width="525"
        d:DataContext="{d:DesignInstance viewModel:MainViewModel}">

    <Grid x:Name="LayoutRoot">
        <ListBox HorizontalAlignment="Left" Height="299" Margin="230,10,0,0" VerticalAlignment="Top" Width="100" 
                 SelectionMode="Multiple"
                 ItemsSource="{Binding Items}">
            <ListBox.ItemContainerStyle>
                <Style TargetType="{x:Type ListBoxItem}">
                    <Setter Property="IsSelected" Value="{Binding IsSelected}"/>  <!--This line-->
                </Style>
            </ListBox.ItemContainerStyle>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding IsSelected}"></TextBlock>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

    </Grid>
</Window>

This example works as expected: a selected item always has True written in it, and False is written in an unselected item.

However, Visual Studio (or Resharper) underlines the word IsSelected on the marked line and the suggestion says Cannot resolve property 'IsSelected' in data context of type 'RoomDesigner.ViewModel.MainViewModel' . It wants to bind to a MainViewModel and not to DataItem somewhy.

I use Visual Studio 13 SP3 and Resharper 8.1.

I'd like to know where this strange behavior comes from and if there is a way to fix it, because it is kind of annoying.

Answer 1

You should set the d:DataContext on the Style element. It is not inferenced automatically for ItemContainerStyle property.

<Style TargetType="{x:Type ListBoxItem}" d:DataContext="{d:DesignInstance viewModel:DataItem}">
    <Setter Property="IsSelected" Value="{Binding IsSelected}"/>  <!--This line-->
</Style>

See a similar question: Specify datacontext type on listbox ItemContainer in style .
Another similar question: How does this setter end up working? (ListView MultiSelect) .