Tree View IsSelected with hierarchical data template - wpf

Question

I have found a couple examples of binding an IsSelected Property in the view model. However none of these deal with a TreeView with Hierachical data templates.
My Hierachy is like this
VM_Part
VM_Step
VM_Step
VM_Step
VM_Part
VM_Step
VM_Step
I would like to be able to select multiple VM_Part instances or Multiple VM_Steps under one part. The idea being I can have a context menu and perform various commands on the selected items
<Window x:Class="NameSpace1.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:local="clr-namespace:Hipot_Sequence_Editor"
xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
mc:Ignorable="d"
Title="MainWindow" Height="677.538" Width="896.456">
<Window.DataContext>
<local:VM_Main></local:VM_Main>
</Window.DataContext>
<Grid>
<TreeView x:Name="treeView" Grid.Column="1" HorizontalAlignment="Left" Height="628" Margin="10.2,10,0,0" VerticalAlignment="Top" Width="237" Grid.RowSpan="2" ItemsSource="{Binding Parts}">
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type viewModels:VM_Part}" ItemsSource="{Binding VM_Steps}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding SequenceNumber}" />
<TextBlock Text=" - "></TextBlock>
<TextBlock Text="{Binding PartNumber}" />
</StackPanel>
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type viewModels:VM_Step}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Name}" />
</StackPanel>
</DataTemplate>
</TreeView.Resources>
</TreeView>
</Grid>
This seems to me the closet example to what I need. I tried the first answered suggested
<TreeView.Resources>
<Style TargetType="TreeViewItem">
<Setter Property="IsSelected"
Value="{Binding Path=IsSelected, Mode=TwoWay}" />
</Style>
</TreeView.Resources>
However it seems that this code assumes IsSelected is in VM_Main and not in VM_Part or VM_Step

Answer 1

each TreeViewItem in a hierarchy
VM_Part TreeViewItem
VM_Step TreeViewItem
VM_Step TreeViewItem
VM_Step TreeViewItem
has its own DataContext (VM_Part or VM_Step)
so if VM_Part and VM_Step have IsSelected property, then style for TreeViewItem is defined correctly
<Style TargetType="TreeViewItem">
<Setter Property="IsSelected"
Value="{Binding Path=IsSelected, Mode=TwoWay}" />
</Style>
however, multiselection in TreeView is probably simpler with CheckBoxes added to item template and bound to view model IsSelected property:
<HierarchicalDataTemplate DataType="{x:Type viewModels:VM_Part}" ItemsSource="{Binding VM_Steps}">
<StackPanel Orientation="Horizontal">
<CheckBox IsChecked="{Binding IsSelected, UpdateSourceTrigger=PropertyChanged}" />
<TextBlock Text="{Binding SequenceNumber}" />
<TextBlock Text=" - "/>
<TextBlock Text="{Binding PartNumber}" />
</StackPanel>
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type viewModels:VM_Step}">
<StackPanel Orientation="Horizontal">
<CheckBox IsChecked="{Binding IsSelected, UpdateSourceTrigger=PropertyChanged}" />
<TextBlock Text="{Binding Name}" />
</StackPanel>
</DataTemplate>