WPF - Binding to CheckBox not working in a HierarchicalDataTemplate - binding

Question

In a WPF treeview I am trying to automatically check the children if the parent node is being checked. I am using a view model for that and a bindable object for the nodes, however all my attempts failed. Here is the code (C# + XAML). Any ideas would be greatly appreciated
<Window x:Class="TestCheckBoxBinding.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestCheckBoxBinding"
Title="Window1" Height="300" Width="300">
<Window.Resources>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="True"/>
</Style>
<HierarchicalDataTemplate DataType="{x:Type local:TestCategory}" ItemsSource="{Binding Tests, Mode=OneTime}">
<Label Content="{Binding Name}"></Label>
</HierarchicalDataTemplate>
<HierarchicalDataTemplate DataType="{x:Type local:Test}" ItemsSource="{Binding Children, Mode=OneTime}">
<StackPanel Orientation="Horizontal">
<CheckBox VerticalAlignment="Center" IsChecked="{Binding IsChecked, Mode=TwoWay}"></CheckBox>
<Label Content="{Binding Name}"></Label>
</StackPanel>
</HierarchicalDataTemplate>
</Window.Resources>
<Grid>
<TreeView ItemsSource="{Binding Categories, Mode=OneTime}"></TreeView>
</Grid>
public class TestsViewModel
{
public static void PopulateList(TestsViewModel vm)
{
TestCategory cat1 = new TestCategory() { Id = 1, Name = "First category" };
Test t1 = new Test() { Name = "Test1" };
Test t2 = new Test() { Name = "Test2" };
Test t3 = new Test() { Name = "Test3" };
t1.AddChild(t2);
t1.AddChild(t3);
Test t4 = new Test() { Name = "Test4" };
cat1.AddTest(t1);
cat1.AddTest(t4);
vm.AddTestCategory(cat1);
TestCategory cat2 = new TestCategory() { Id = 2, Name = "Second category" };
Test t5 = new Test() { Name = "Test1" };
Test t6 = new Test() { Name = "Test2" };
Test t7 = new Test() { Name = "Test3" };
t6.AddChild(t7);
Test t8 = new Test() { Name = "Test4" };
cat2.AddTest(t5);
cat2.AddTest(t6);
cat2.AddTest(t8);
vm.AddTestCategory(cat2);
}
private readonly IEnumerable<TestCategory> categories = new List<TestCategory>();
public IEnumerable<TestCategory> Categories { get { return categories; } }
public void AddTestCategory(TestCategory testCategory)
{
((IList<TestCategory>)categories).Add(testCategory);
}
}
public class TestCategory
{
public int Id { get; set; }
public string Name { get; set; }
private readonly IEnumerable<Test> tests = new List<Test>();
public IEnumerable<Test> Tests { get { return tests; } }
public void AddTest(Test t)
{
((IList<Test>)tests).Add(t);
}
}
public class Test : INotifyPropertyChanged
{
private string name;
public string Name
{
set
{
if (name != value)
{
name = value;
this.OnPropertyChanged("Name");
}
}
get { return name; }
}
public bool? isChecked = false;
public bool? IsChecked
{
get { return isChecked; }
set
{
if (isChecked != value)
{
isChecked = value;
if (children.Count() > 0)
{
foreach (var test in children)
{
test.isChecked = value;
test.Name += ".";
}
}
this.OnPropertyChanged("IsChecked");
}
}
}
public void AddChild(Test test)
{
((IList<Test>)children).Add(test);
}
private readonly IEnumerable<Test> children = new List<Test>();
public IEnumerable<Test> Children
{
get { return children; }
}
#region INotifyPropertyChanged Members
// Create the OnPropertyChanged method to raise the event
protected void OnPropertyChanged(string propName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
#endregion
}

Answer 1

Oups, child checkboxes are not being checked because I wasn't setting their IsChecked property. I was setting the isChecked field, which bypasses the property setter and prevents PropertyChanged from being raised.