binding items to wpf treeview displays nothing?

Question

Why does my wpf treeview not display the content when i've set the itemsource in the xaml? It only appears to show the data when i set this property in the CS file using this

trvFamilies.ItemsSource = families;

Is it maybe not updating because im not triggering and updating somehow in the xaml? I'm not sure what to change to get this to work correctly.

ViewModel.cs

using System;
using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Input;

namespace WpfApplication1
{
    public class ViewModel : ObservableObject
    {
        private ObservableCollection<Family> families; 
        public ObservableCollection<Family> Families
        {
            get { return families; }
            set
            {
                families = value;
                NotifyPropertyChanged("Families");
            }
        }

        public ViewModel()
        {
            // FAMILIES
            Family family1 = new Family() { Name = "The Doe's" };
            family1.Members.Add(new FamilyMember() { Name = "John Doe", Age = 42 });
            family1.Members.Add(new FamilyMember() { Name = "Jane Doe", Age = 39 });
            family1.Members.Add(new FamilyMember() { Name = "Sammy Doe", Age = 13 });
            Families.Add(family1);

            Family family2 = new Family() { Name = "The Moe's" };
            family2.Members.Add(new FamilyMember() { Name = "Mark Moe", Age = 31 });
            family2.Members.Add(new FamilyMember() { Name = "Norma Moe", Age = 28 });
            Families.Add(family2);
        }
    }

    public class Family
    {
        public Family()
        {
            this.Members = new ObservableCollection<FamilyMember>();
        }

        public string Name { get; set; }

        public ObservableCollection<FamilyMember> Members { get; set; }
    }

    public class FamilyMember
    {
        public string Name { get; set; }

        public int Age { get; set; }
    }
}

ObservableObject.cs

using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;

namespace WpfApplication1
{
    public class ObservableObject : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public void NotifyPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}

MainWindow.xaml

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:self="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="300"
        WindowStartupLocation="CenterScreen">
    <Grid Margin="5">

        <TreeView Name="trvFamilies" ItemsSource="{Binding self:families}" Grid.Row="1" Grid.ColumnSpan="2">
            <TreeView.Resources>
                <HierarchicalDataTemplate DataType="{x:Type self:Family}" ItemsSource="{Binding Members}">
                    <StackPanel Orientation="Horizontal">
                        <Label VerticalAlignment="Center" FontFamily="WingDings" Content="1"/>
                        <TextBlock Text="{Binding Name}" />
                    </StackPanel>
                </HierarchicalDataTemplate>
                <DataTemplate DataType="{x:Type self:FamilyMember}">
                    <StackPanel Orientation="Horizontal">
                        <Label VerticalAlignment="Center" FontFamily="WingDings" Content="2"/>
                        <TextBlock Text="{Binding Name}" />
                    </StackPanel>
                </DataTemplate>
            </TreeView.Resources>
        </TreeView>

    </Grid>
</Window>

You now have to bind to your ViewModel instead of your window ofcourse, check the debug output that might say that Families do not exist (anymore) on self — Icepickle, Oct 16 '15 at 22:27

score 0 · Accepted Answer · edited May 23 '17 at 11:59

0

Currently your are binding to a public field:

  public List<Family> families

But a binding source (the data) needs to be a public property. For collection types, in WPF you usually use a ObservableCollection

So change your property to:

public ObservableCollection<Family> Families { get; set; }

Additional info:

Usually the property you bind to does not reside in the view class (here: not in your window), but in a separate class called "view model" which should implement the INotifyPropertyChanged interface.

Take a look here for more info: Model-View-ViewModel-MVVM-Explained

In the end, your view model should look like this:

public ObservableCollection<Family> Families
{
    get { return _families; }
    set
    {
        _families= value;
        RaisePropertyChanged("Families");
    }
}
public ObservableCollection<Family> _families; 

protected void RaisePropertyChanged(string propertyName)
{
    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler != null)
    {
        handler(this, new PropertyChangedEventArgs(propertyName));
    }
}

public event PropertyChangedEventHandler PropertyChanged;

With the new view model class in place, the binding can be changed to

ItemsSource="{Binding Families}"

Finally you need to set you new view model class as DataContext in your window, see here.

edited May 23 '17 at 11:59

Community

1
1

answered Oct 16 '15 at 21:29

Martin

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would you be able to modify my code to demonstrate what that would look like? – JokerMartini Oct 16 '15 at 21:32
I would always suggest that an `ObservableCollection` is privately declared and instantiated as readonly and doesn't have a public setter, so that people can only clear the list or add items, it doesn't really need the RaisePropertyChanged call in this case – Icepickle Oct 16 '15 at 21:39
I changed the mistake with the string, copy paste error :-) Well yes, you could make the setter of `Families` private. I tend to always implement `INotifyPropertyChanged` in the properties are bind to, just to avoid potential errors. – Martin Oct 16 '15 at 21:42
it's more to protect myself from the fact that people might bind to the `CollectionChanged` event, and not observing if the Property Families get changed in the ViewModel (+they also have to keep a reference to it to unregister from the old `ObservableCollection`. But the `RaisePropertyChanged` call is also unnecessary at that time, so it really simplifies things. Btw, your private _families is declared as public here ;) – Icepickle Oct 16 '15 at 21:45
so ive updated the post above and it appears to not show still? Why would this be. check out my latest code – JokerMartini Oct 16 '15 at 22:02
Change your binding to ItemsSource="{Binding Families}" and then you need to set you new view model class as `DataContext` in your window, see here: http://stackoverflow.com/a/4590471/4424024 – Martin Oct 16 '15 at 22:27

binding items to wpf treeview displays nothing?

1 Answers1