Develop Reference

How do you add a button to a TreeView using a HierarchicalDataTemplate?

I've got a TreeView that is constructed like this:
//This is for dynamically building a treeview with templates from an XML file
XmlTextReader xmlReader1 = new XmlTextReader("HierarchicalDataTemplate1.xml");
HierarchicalDataTemplate hierarchicalDataTemplate1 = XamlReader.Load(xmlReader1) as HierarchicalDataTemplate;
And it reads an XML file like this:
<HierarchicalDataTemplate xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" ItemsSource="{Binding XPath=SubCategory}">
<TextBlock FontSize="36" FontFamily="K22 Monastic" Text="{Binding XPath=#CategoryName}" />
<Button>Add Subordinate Unit</Button>
</HierarchicalDataTemplate>
But it throws a runtime error on adding the button:
''Template' property has already been set on 'HierarchicalDataTemplate'.' Line number '3' and line position '4'.
Is what I'm trying to do possible? If I take out the script for adding a button everything works fine.
Thanks!

One obvious error is that you've got two elements at the root level of the template's visual tree. You can't do that. A DataTemplate or HierarchicalDataTemplate can have only one child. So your first step is to make that one child a control that supports multiple children of its own, then put your TextBlock and your Button in that. StackPanel is a good one:
<HierarchicalDataTemplate
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
ItemsSource="{Binding XPath=SubCategory}"
>
<StackPanel Orientation="Horizontal">
<TextBlock
FontSize="36"
FontFamily="K22 Monastic"
Text="{Binding XPath=#CategoryName}"
/>
<Button>Add Subordinate Unit</Button>
</StackPanel>
</HierarchicalDataTemplate>
It's interesting to note that when I paste your template XAML into the XAML designer, I get a different error: "The property 'VisualTree' is set more than once" -- but when I duplicate your XamlReader.Load(), code, I get the same exception and message as you (and the same fix corrects it).
Google turns up zero results for "Template property has already been set on HierarchicalDataTemplate". Well, maybe it'll have one now.

Overwrite ListBoxitem?

I'm new to WPF and I have this ListBox which I want to instantiate with a specific ListBoxItem, so the user knows what to do with the ListBox.
<ListBox Name="DbListBox"
Grid.Column="3"
HorizontalAlignment="Left"
Height="246"
Margin="0,99,0,0"
Grid.Row="1"
VerticalAlignment="Top"
Width="211"
SelectionMode="Single"
SelectedItem="{Binding Path=selectedDB,Mode=TwoWay}"
AllowDrop="True"
Drop="DbListBox_Drop">
<ListBoxItem Name="ListBoxItem" FontStyle="Italic">Drag .db file here or add below</ListBoxItem>
</ListBox>
Then I have some code which adds a collection of items to the ItemsSource of this ListBox, but I can't do that since the ItemsSource is not empty
DbListBox.ItemsSource = DbCollection;
My question is, how can I start up the ListBox with the item inserted first, and then when DbCollection is added to it, it simply overwrites the first ListBoxItem?

When using WPF properly, we'd normally have something like this, where a collection property would be data bound to the ListBox.ItemsSource property:
<ListBox ItemsSource="{Binding SomeCollectionProperty}" />
Once we have this XAML, we don't need to touch the ListBox again, as we can add or remove items from the data bound collection and they will magically appear (or disappear) from the ListBox:
SomeCollectionProperty.Add(new SomeDataType());
SomeCollectionProperty.Remove(someItemFromCollection);
The SomeDataType used here is up to you... it depends on what you want to display in your items. If it was just a plain string for example, then you could simply do this to add your initial item into the collection:
SomeCollectionProperty.Add("Drag .db file here or add below");
If you wanted to make that item look different to the others then you'd need to data bind a custom class that has a Text property and FontStyle property for example. You could data bind these properties in a DataTemplate to design each item to be exactly as you want it. However, that's a completely different question.
To find out more about these things, you can read the Data Binding Overview and Data Templating Overview page on MSDN.

INotifyPropertyChanged not working with WPF data binding

I have a combobox in my MainWindow.xaml file like so:
<ComboBox Name="material1ComboBox"
HorizontalAlignment="Center"
MinWidth="100"
ItemsSource="{Binding ViewProperties.MaterialDropDownValues}"
SelectedValue="{Binding ViewProperties.Material1SelectedValue}"
SelectionChanged="Material1ComboBoxSelectionChanged">
</ComboBox>
I've assigned the datacontext in the codebehind using this.datacontext = this.
I created a ViewProperties that is accessed as a property in the MainWindow and is a class that implements INotifyPropertyChanged and contains the MaterialDropDownValues as a property.
I even changed the the MaterialDropDownValues to be an ObservableCollection.
The problem is that the databinding works on initialisation however if the MaterialDropDownValues property is changed the combobox values are not updated.
I have the following in the ViewProperties class:
public ObservableCollection<string> MaterialDropDownValues
{
get { return this.materialDropDownValues; }
set
{
this.materialDropDownValues = value;
OnPropertyChanged("MaterialDropDownValues");
}
}
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
Any ideas why this is not working? All the other answers I could find advised to implement INotifyPropertyChanged and make the property an observablecollection.

Solution 1:
Dont recreate this.materialDropDownValues try to do
this.materialDropDownValues.Clear();
foreach(var mystring in myStrings)
this.materialDropDownValues.Add(mystring);
for all new items. If this doesnt work then try solution 2...
Solution 2:
As per my experience, I think ObservableCollection of primitive types like int, string, bool, double etc. does not refresh on Property Change notification if ItemsControl.ItemTemplate is not specified.
<ComboBox Name="material1ComboBox"
HorizontalAlignment="Center"
MinWidth="100"
ItemsSource="{Binding ViewProperties.MaterialDropDownValues}"
SelectedValue="{Binding ViewProperties.Material1SelectedValue}"
SelectionChanged="Material1ComboBoxSelectionChanged">
<ComboBox.ItemTemplate>
<DataTemplate DataType="{x:Type System:String}">
<TextBlock Text="{Binding}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
This is because the itemscontrol's items container creates non-observable item containers in it for primitive data by simply copying item.ToString(). In the code above the {Binding} should update the data changes when the whole items source is changed.
Let me know if this works.

When I bump into things like this, the first thing I do is play around with the binding mode. Something like:
ItemsSource="{Binding Path=ViewProperties.MaterialDropDownValues, Mode=TwoWay}"
That sometimes trips you up. The other thing I would make sure of is that if you're instantiating new ViewProperties object(s) following your initial load, you notify change on that. If you don't, the XAML will be referring to an outdated version of the object while your code behind/view model is operating on a different one.

Edit in response to comments
None of the below solved the problem, but is left as a reference.
Original Answer
The problem is that you have not specified the DataContext for your view, which is where WPF looks for Binding values by default.
Provided that your ViewProperties property on MainWindow is public you can simply change your binding to:
ItemsSource="{Binding ViewProperties.MaterialDropDownValues,
RelativeSource={RelativeSource FindAncestor, AncestorType=Window}"
This causes WPF to look for the property value on the first occurence of Window that it finds above the combobox in the visual tree.
Alternatively, you can just set the Window.DataContext property to your instance of ViewProperties and change the binding to the following:
ItemsSource="{Binding MaterialDropDownValues}"
Either of these will work, but I would suggest using the latter as it is closer to the MVVM pattern that is generally preferred in WPF/XAML applications.

what happens if you change your xaml to
<ComboBox Name="material1ComboBox"
HorizontalAlignment="Center"
MinWidth="100"
DataContext="{Binding ViewProperties}"
ItemsSource="{Binding MaterialDropDownValues}"
SelectedValue="{Binding Material1SelectedValue}"
SelectionChanged="Material1ComboBoxSelectionChanged">
</ComboBox>
nevertheless you should just instantiate your collection once and just use remove, add and clear when you use a OberservableCollection.

Posting this in case anyone else runs into this. I came up this as the best search result matching my symptoms, but it turns our that none of the answers worked above for me.
I was using WinUI3 and apparently it uses the newer x:Bind syntax for it's XAML. Apparently x:Bind defaults it's Mode to OneTime which is why it wouldn't update after the first value (I also tried Binding but couldn't get that to work)
From: <TextBlock Text="{x:Bind MyField}" x:Phase="1" Margin="0,5,0,5"/>
To: <TextBlock Text="{x:Bind MyField, Mode=OneWay}" x:Phase="1" Margin="0,5,0,5"/>
So if you are using x:Bind, make sure set Mode=OneWay AND implement INotifyPropertyChanged and then things should work

Find a control within a ListViewItem

I have a ListView displaying a list of items containing mainly two properties.
Each of these properties should ideally be chosen from two comboboxes.
Moreover, the choices available in the second combobox is depends on the first.
So here is the idea of the code I used:
<ListView>
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel>
<ComboBox Name="combo1"
ItemsSource="{DynamicResource combo1Source}"
SelectedItem="{Binding FirstProperty}"
SelectionChanged="combo_SelectionChanged">
<ComboBox Name="combo2"
ItemsSource="{DynamicResource combo2Source}"
SelectedItem="{Binding SecondProperty}">
</StackPanel>
<DataTemplate>
<ListView.ItemTemplate>
</ListView>
The thing is, I don't know how to get the reference to combo2 from within combo_SelectionChanged (in C#).
Could you show me how to proceed?

The easiest thing you can do is add a Tag to combo1:
<ComboBox Name="combo1" Tag="{x:Reference combo2}" ... />
Which you then can just get from the sender in the event handler, e.g.
var combo2 = (sender as FrameworkElement).Tag as ComboBox;
Alternatively you could get the StackPanel from the Parent property and just take (ComboBox)Children[1]. I would not do this though as is breaks if the structure of your template changes.

You should not have a reference to combo2, but you should update the Collection combo2Source which is bound as ItemsSource for combo2...
So in the combo_SelectionChanged you just load the possible values for the actual selection of combo1 to the combo2Source Collection.
EDIT: To prevent thats its for all items the same:
Add a ValueConverter which choses for a selectedItem the corresponding collection of possible values:
<ComboBox ItemsSource="{Binding ElementName=Combo1, Path=SelectedItem, Converter={StaticResource SubSelectionConverter}}" />
Example of ValueConverter:
private Dictionary<Object, List<Object>> _PossibleValues;
public object Convert(Object data, ....)
{
if(PossibleValues.ContainsKey(data))
{
//return the possible values for the actual selected parent item
return(PossibleValues(data));
}
return null;
}

Can have look here on my question and different responses and the solution I found for my specific project:
Find an element in Data Template
Hope this helps.
Regards.

Bind a collection to a WPF ListBox

Update: I've updated the code based on your help so far, and still no luck. When the application loads the ListBox has no items. I assign junk values to Customers in the windows's contructor, and then am also trying to set the ListBox's DataContext as follows:
CustomerList.DataContext = Customers;
--- Original Question (with updated code) ---
I'm having trouble with databinding in a WPF project.
I have a class, Customer, as follows:
public class Customer
{
public String Name { get; set; }
public String Email { get; set; }
}
In my XAML's code behind I have a collection of customers as follows:
public List<Customer> Customers { get; set; }
I'm trying to bind each customer to a ListBox with a ListItemTemplate displaying the customer's information (name/email) in TextBoxes along with a button which locks/unloacks the TextBoxes (sets the IsEnabled property to true or false).
What's the best way to go about this?
So far I've been tryingt he following with no success.
In the XAML I currently have the following (ignoring the toggle part for now, I'm just trying to get the collection itself to be listed.):
<Window.Resources>
<CollectionViewSource x:Key="Customers" Source="{Binding Path=Customers, Mode=TwoWay}"/>
<DataTemplate x:Key="Customer">
<StackPanel Orientation="Horizontal">
<TextBox Content="{Binding Name}" />
<TextBox Content="{Binding Email}" />
</StackPanel>
</DataTemplate>
</Window.Resources>
<StackPanel>
<ListBox ItemsSource="{Binding Source={StaticResource Customers}}"
ItemTemplate="{StaticResource ResourceKey=Customer}"
Name="CustomerList"
Height="300" />
</StackPanel>

You need to change
ItemsSource="{Binding Source=Customers}"
to
ItemsSource="{Binding Source={StaticResource Customers}}" DataContext="{StaticResource Customers}"

Code similar to the updated one works for me after changing
<TextBox Content="{Binding Name}" />
to
<TextBox Text="{Binding Name}" />
As TextBox doesn't have Content property(like a Label), the former refused to compile in VS.
Well, it is set to Text in definition:
[ContentPropertyAttribute("Text")]
public class TextBox : TextBoxBase, IAddChild
But I thought it is only used between the brackets(<TextBox>Like so</TextBox>)?
Could this be the source of the problem?

Try setting the ItemsSource of your CustomerList as follows: ItemsSource="{Binding}". You've set the DataContext of the ListBox to the list of customers, you need to set the ItemsSource to the same collection, hence, the direct binding.
Another thing that you can do, in case you prefer to use the CollectionViewSource, is to set the DataContext of your window to the same class DataContext=this, because without this, the resource definition won't be able to locate the "Customers" collection that you defined in the code behind. If you do this, however, you don't need CustomerList.DataContext = Customers; because you're directly assigning the ItemsSource to a static resource, not relatively to the DataContext.
One more thing. I think you should give the CollectionViewSource and the corresponding collection in the code behind different names. This isn't going to cause a runtime issue, but it makes it hard to maintain the code ;)
Hope this helps :)