Binding to a viewmodel property in a DataTemplate
binding, datatemplate, properties, wpf, xaml
Solution
When you are in a DataTemplate, your DataContext is the data templated object, in this case an `Item`. Thus, the DataContext of the CheckBox in the DataTemplate is an `Item`, not your `ItemViewModel`. You can see this by your `<TextBlock Text="{Binding ItemName}"/>`, which binds to a property on the `Item` class. The Binding to IsCheckBoxVisible is trying to find a property called IsCheckBoxVisible on `Item`.
There are a couple of ways around this, but by far the easiest is to do this:
On your Window (in the xaml), give it and x:Name. Eg:
<Window [...blah blah...]
x:Name="MyWindow">
Change your binding to look like this:
<CheckBox Grid.Column="1"
Visibility="{Binding DataContext.IsCheckBoxVisible, ElementName=MyWindow, Converter={StaticResource VisibilityConverter}}">
We're using the Window as the source for the Binding, then looking at its DataContext property (which should be your `ItemViewModel`, and then pulling off the IsCheckBoxVisible property.
Another option, if you want something fancier, is to use a proxy object to reference your DataContext. See this article on DataContextProxy.
Problem
I'm fairly new to XAML but enjoying learning it. The thing I'm really struggling with is binding a property to an element in a `DataTemplate`. I have created a simple WPF example to, (hopefully,) explain my problem. I this example I am trying to bind the `Visibility` property of a `CheckBox` in a `DataTemplate` to a Property in my viewmodel. (Using this scenario purely for learning/demo.) I have a simple DataModel named `Item`, but is of little relevance in this example. ``` class Item : INotifyPropertyChanged { // Fields... private bool _IsRequired; private string _ItemName; ``` And a fairly simple View Model named ItemViewModel. ``` class ItemViewModel : INotifyPropertyChanged { private ObservableCollection<Item> _Items; private bool _IsCheckBoxChecked; private bool _IsCheckBoxVisible; public ObservableCollection<Item> Items { get { return _Items; } set { _Items = value; } } public bool IsCheckBoxChecked { get { return _IsCheckBoxChecked; } set { if (_IsCheckBoxChecked == value) return; _IsCheckBoxChecked = value; if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs("IsCheckBoxChecked")); PropertyChanged(this, new PropertyChangedEventArgs("IsCheckBoxVisible")); } } } public bool IsCheckBoxVisible { get { return !_IsCheckBoxChecked; } set { if (_IsCheckBoxVisible == value) return; _IsCheckBoxVisible = value; if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("IsCheckBoxVisible")); } ``` (Constructors and `INotifyPropertyChanged` implementation omitted for brevity.) Controls laid out in MainPage.xaml as follows. ``` <Window.Resources> <local:VisibilityConverter x:Key="VisibilityConverter"/> </Window.Resources> <Window.DataContext> <local:ItemViewModel/> </Window.DataContext> <Grid> <StackPanel> <CheckBox x:Name="checkBox" Content="Hide CheckBoxes" FontSize="14" IsChecked="{Binding IsCheckBoxChecked, Mode=TwoWay}" /> <ListView ItemsSource="{Binding Items}" HorizontalContentAlignment="Stretch" > <ListView.ItemTemplate > <DataTemplate> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="*"/> <ColumnDefinition Width="Auto"/> </Grid.ColumnDefinitions> <TextBlock Text="{Binding ItemName}"/> <CheckBox Grid.Column="1" Visibility="{Binding IsCheckBoxVisible, Converter={StaticResource VisibilityConverter}}" > <CheckBox.DataContext> <local:ItemViewModel/> </CheckBox.DataContext> </CheckBox> </Grid> </DataTemplate> </ListView.ItemTemplate> </ListView> <StackPanel Orientation="Horizontal" Margin="4,4,0,0"> <TextBlock Text="IsCheckBoxVisible:"/> <TextBlock Text="{Binding IsCheckBoxVisible}" Margin="4,0,0,0" FontWeight="Bold" /> </StackPanel > <Button Content="Button" Visibility="{Binding IsCheckBoxVisible, Converter={StaticResource VisibilityConverter}}" Margin="4,4,4,4"/> </StackPanel> </Grid> ``` The 'Hide CheckBoxes' checkbox is bound to `IsCheckBoxChecked` and is used to update `IsCheckBoxVisible`. I've also added a couple of extra controls below the `DataTemplate` to prove, (to myself,) the everything works.) I have also implemented Jeff Wilcox's value converter. (Thank you.) http://www.jeff.wilcox.name/2008/07/visibility-type-converter/ When I run the app, checking and unchecking the 'Hide Checkbox', controls outside the `DataTemplate` function as expected but, alas, the `Checkbox` inside the data template remains unchanged. I have had success with: ``` IsVisible="{Binding IsChecked, Converter={StaticResource VisibilityConverter}, ElementName=checkBox}" ``` But I'm not just trying mimic another control but make decisions based on a value. I would REALLY appreciate any help or advice you can offer. Thank you.