I would like to bind third column to a CollectionBindingTwo
property that is within Window's DataContext and not inside DataContext of an Items from CollectionBindingOne
.
By defining the second collection inside <DataGrid>
WPF assumes local scope or something, and points to a property within Items of ItemsSource (CollectionBindingOne
).
<DataGrid DockPanel.Dock="Top" ItemsSource="{Binding CollectionBindingOne}" AutoGenerateColumns="False">
<DataGridTextColumn Header="One" Binding="{Binding PropOne}"/>
<DataGridTextColumn Header="Two" Binding="{Binding PropTwo}"/>
<DataGridComboBoxColumn Header="Three" ItemsSource="{Binding CollectionBindingTwo}"/>
</DataGrid>
For example, this works because ComboBox
is not inside a <DataGrid>
:
<ComboBox IsEditable="True" ItemsSource="{Binding CollectionBindingTwo}"></ComboBox>
A dependency property can reference a value through data binding. Data binding works through a specific markup extension syntax in XAML, or the Binding object in code. With data binding, determination of the final property value is deferred until run time, at which time the value is obtained from a data source.
A DependencyProperty maintains a static reference of all the DependencyProperty you register in WPF object hierarchy. It maintains a HashTable named PropertyFromName which it uses internally to get the DependencyProperty object. So in other word, each dependencyProperty object is registered in a global HashTable.
Dependency properties are used when you want data binding in a UserControl , and is the standard method of data binding for the WPF Framework controls. DPs have slightly better binding performance, and everything is provided to you when inside a UserControl to implement them.
A Dependency Property is a property whose value depends on the external sources, such as animation, data binding, styles, or visual tree inheritance. Not only this, but a Dependency Property also has the built-in feature of providing notification when the property has changed, data binding and styling.
The DataGridComboBoxColumn is not a part of the Visual Tree so the usual RelativeSource/ElementName binding formats won't work. You can use a workaround by defining the ElementStyle and EditingStyle where those binding formats will work. Another option is to use a BindingProxy which I use for other spots and will save some XAML when there is no other reason to define an ElementStyle/EditingStyle.
This is the BindingProxy class which inherits from Freezable.
public class BindingProxy : Freezable
{
#region Overrides of Freezable
protected override Freezable CreateInstanceCore()
{
return new BindingProxy();
}
#endregion
public object Data
{
get { return (object)GetValue(DataProperty); }
set { SetValue(DataProperty, value); }
}
// Using a DependencyProperty as the backing store for Data.
// This enables animation, styling, binding, etc...
public static readonly DependencyProperty DataProperty =
DependencyProperty.Register("Data",
typeof(object),
typeof(BindingProxy),
new UIPropertyMetadata(null));
}
Now your xaml looks like this:
<DataGrid DockPanel.Dock="Top"
ItemsSource="{Binding CollectionBindingOne}"
AutoGenerateColumns="False">
<DataGrid.Resources>
<helper:BindingProxy x:Key="proxy"
Data="{Binding }" />
</DataGrid.Resources>
<DataGrid.Columns>
<DataGridTextColumn Header="One"
Binding="{Binding PropOne}" />
<DataGridTextColumn Header="Two"
Binding="{Binding PropTwo}" />
<DataGridComboBoxColumn Header="Three"
ItemsSource="{Binding Data.CollectionBindingTwo,
Source={StaticResource proxy}}" />
</DataGrid>
Don't forget to declare the helper namespace import at the top of your Window/UserControl.
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