Source versus DataContext in XAML

Which of these methods is best?

<Window.Resources>
    <sys:Int16 x:Key="MyValue">123</sys:Int16>
</Window.Resources>

<StackPanel>

    <!-- method 1 -->
    <TextBlock Text="{Binding}" DataContext="{StaticResource MyValue}" 开发者_StackOverflow/>

    <!-- method 2 -->
    <TextBlock Text="{Binding, Source={StaticResource MyValue}}" />

</StackPanel>

---

As with many "which is better" questions. I would say that "it depends" on the context.

They both exist because they both can serve a purpose in different contexts. Given only what you have shown above, I would choose Example 2.

When you set the DataContext, however, all of its children will inherit that DataContext. So maybe instead you are using a Button. And within you Button, you want to jazz it up a bit and display the text four times each with a different color. As you can see below, I would then choose Example 1.

Example 1: (note the DataContext is on the button, and the TextBlocks don't need the Source like they do in Example 2)

<Button DataContext="{StaticResource MyValue}" Height="Auto" Width="Auto" HorizontalAlignment="Center" VerticalAlignment="Center">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition />
        </Grid.RowDefinitions>
        <TextBlock Grid.Row="0" Grid.Column="0" Text="{Binding}" Foreground="Red" />
        <TextBlock Grid.Row="1" Grid.Column="0" Text="{Binding}" Foreground="Blue" />
        <TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding}" Foreground="Yellow"/>
        <TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding}" Foreground="Green" />
    </Grid>
</Button>

Example 2:

<Button Height="Auto" Width="Auto" HorizontalAlignment="Center" VerticalAlignment="Center">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition />
        </Grid.RowDefinitions>
        <TextBlock Grid.Row="0" Grid.Column="0" Text="{Binding, Source={StaticResource MyValue}}" Foreground="Red" />
        <TextBlock Grid.Row="1" Grid.Column="0" Text="{Binding, Source={StaticResource MyValue}}" Foreground="Blue" />
        <TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding, Source={StaticResource MyValue}}" Foreground="Yellow"/>
        <TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding, Source={StaticResource MyValue}}" Foreground="Green" />
    </Grid>
</Button>

When you're binding to a simple object that only has one representation like an Int16 in your case, you're probably only going to bind and display that value once, and thus option 2 makes most sense.

A good rule of thumb... if you find yourself setting the 'Source' to the same thing more than one binding, you should probably just bind the DataContext of a common parent FrameworkElement.

---

I would say that if I had to choose between the two, I would go with method 2. DataContext is really more for Databinding an item to a more complex underlying object and eases the databinding of many data values.

Just out of curiosity, why are you doing it this way? Does your code change the value of MyValue at some point? Is there no better way for you to do it for some reason?

---

The DataContenxt DependencyProperty allows you to easily bind across all of proeprties for a DependencyObject.

The Source DependenceyProperty of a Binding allows you to point that specific binding to the source you want, regardless of the DataContext.

This becomes really helpful when you are doing more complex bindings for ListViews. For instance:

<Window.Resources>
  <local:MyConverter x:Key="MyConverter" />
</Window.Resources>
<Grid>
  <ComboBox ItemsSource="{Binding Source={StaticResource MyConverter}, Path=DisplayValues}" DataContenxt={Binding ElementName=lvwItems Path=SelectedItem} SelectedItem="{Binding Converter={StaticResource MyConverter}"/>
<ListView Name="lvwItems"......

The above example just shows off that I set the itemssource to a property in the 'MyConverter' called DisplayValues, the datacontext is what I am working with on that combobox though, which is handling the SelectedItem property of the ListView named 'lvwItems'.

Hope this helps.