In this post I will try to illustrate the difference between DataContext and
ItemsSource property in Silverlight/WPF. These two properties don't serve the
same purpose.
- DataContext expects an object type where ItemsSource expects IEnumerable type
objects.
- DataContext is a dependency property is exposed by FrameworkElement base
class,where as ItemsSource is defined by the ItemsControl class. All the
descendants of FrameworkElement can utilize the DataContext property and set an
object to its value. But we can only set a type of IEnumerable(or instance of
class that derives from).
- DataContext does not generate template, it only used to hold common data for
other controls to bind. In terms of ItemsSource property, it is mainly used to
generate template regardless of you set it in XAML or in the code behind.
- DataContext is mainly used to hold common data that other child want to
share. Thus it can be inherited by other child elements without problem. But for
ItemsSource, it not used to share data in the visual tree. It is only valid for
the element that defined. There is still one thing to be noted is that the child
element can override the DataContext of the perent DataContext no mater directly
or indirectly.
Examples:
Suppose we have a Person Class which has a property Name. Now in Xaml we can say
like:
<StackPanel
x:Name="Parent">
<StackPanel.Resources>
<local:Person
x:Key="person">
</StackPanel.Resources>
<ListBox
ItemsSource="{Binding
Source={StaticResource
person}}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBox
Text="{Binding
Path=Name}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</StackPanel>
If you run this code in the ListBox you will get to see values depending on
List<Person> object. But if we change the ItemsSource to DataContext then you
will be not able to see anything because DataContext doesn't generate templates
in any cases. If you set datacontext still you have to set the ItemsSource
property like this:
<ListBox
DataContext="{Binding
Source={StaticResource
person}}"
ItemsSource="{Binding}">
Conclusion:
In a word, if we have several child elements that will share a common data
source, we can set DataContext property for the parent elements. And we use
ItemsSource for ItemsSource in most cased to generate template. Like:
<StackPanel
DataContext="{Binding
Person"}>
<TextBox
Text="{Binding
FName}"/>
<TextBox
Text="{Binding
LName}"/>
</StackPanel>
Hope this helps you......