What is DataContext for?

data-binding, wpf

Solution

When you write

<Label name="myLabel" Content="{Binding Path=Name}" />

you are binding to `myLabel.DataContext.Name`, and not `myLabel.Name`.

The XAML in WPF is just a pretty user interface to display and interact with the actual data, otherwise known as the `DataContext`. The purpose of other binding sources (`RelativeSource`, `ElementName`, etc) is to point to another property that doesn't exist in the current control's `DataContext`

So suppose you have a Window. Without setting the DataContext, the window still displays but there is no data behind it.

Now suppose to set `myWindow.DataContext = new ClassA();`. Now the data that the window is displaying is `ClassA`. If `ClassA` has a property called `Name`, I could write a label and bind it to `Name` (such as your example), and whatever value is stored in `ClassA.Name` would get displayed.

Now, suppose `ClassA` has a property of `ClassB` and both classes have a property called `Name`. Here is a block of XAML which illustrates the purpose of the DataContext, and an example of how a control would refer to a property not in it's own DataContext

<Window x:Name="myWindow"> <!-- DataContext is set to ClassA -->
    <StackPanel> <!-- DataContext is set to ClassA -->

        <!-- DataContext is set to ClassA, so will display ClassA.Name -->
        <Label Content="{Binding Name}" />

         <!-- DataContext is still ClassA, however we are setting it to ClassA.ClassB -->
        <StackPanel DataContext="{Binding ClassB}">

            <!-- DataContext is set to ClassB, so will display ClassB.Name -->
            <Label Content="{Binding Name}" />

            <!-- DataContext is still ClassB, but we are binding to the Window's DataContext.Name which is ClassA.Name -->
            <Label Content="{Binding ElementName=myWindow, Path=DataContext.Name}" /> 
        </StackPanel>
    </StackPanel>
</Window>

As you can see, the DataContext is based on whatever data is behind the UI object.

Update: I see this question so often from new WPF users that I expanded this answer into a post on my blog: What is this “DataContext” you speak of?

Problem

As a continuation of the question Linking DataContext with another property in WPF. At the very end of the research I was very surprised to find out that when one writes something like that: ``` <Label Content="{Binding Path=Name}" /> ``` The `DataContext` against which the `Content` property is binded is of the `Label` control itself! The fact that it still works is due to the default inheritance of the DataContext value from the nearest parent. But if you have this label wrapped in a custom control, and you don't want to bind your data to the `DataContext` property of that control, you would more likely love to have: ``` <Controls:SearchSettings Settings="{Binding Path=Settings}" /> ``` And here you are. Now you need to set `Settings` as the `DataContext` for the `SearchSettings` control, for `Label` inside to bind against, but you can't, because that will trigger re-binding of `Settings` property. I can't see the point in mixing binding properties using different sources: `DataContext`, by `ElementName`, etc. So why would I ever use `DataContext`?

Original source