Binding ComboBox Item with a text property of different DataContext - wpf

Question

I have a ComboBox as below. What I want is to bind the SelectedItem value to a Text property of a DataContext so that another DataTemplate can show the Image. Please note that the ComboBox and target Image elements are on two different DataTemplates so that's why I need to update the Text property (ImageName) of DataContext in the backend.
<ComboBox x:Name="cboOverlay" Grid.Row="0" Grid.Column="1" SelectedIndex="0" >
<ComboBoxItem Name="BC_OL" IsSelected="True">
<StackPanel Orientation="Horizontal">
<Image Source="Images\BC_OL.jpg" Width="100" Height="25" Canvas.Top="0" Canvas.Left="0" />
<TextBlock Width="100" VerticalAlignment="Center" TextAlignment="Center"><Bold>Image1</Bold></TextBlock>
</StackPanel>
</ComboBoxItem>
<ComboBoxItem Name="Indian_OL">
<StackPanel Orientation="Horizontal">
<Image Source="Images\Indian_OL.jpg" Width="100" Height="25" Canvas.Top="0" Canvas.Left="0" />
<TextBlock Width="100" VerticalAlignment="Center" TextAlignment="Center"><Bold>Image2</Bold></TextBlock>
</StackPanel>
</ComboBoxItem>
</ComboBox>
<Image Source="{Binding Path=Image}" Width="81" Height="25" Canvas.Top="0" Canvas.Left="0" />

Answer 1

You can set each item to have a specific data context.
I'm not sure in your xaml which item you are trying to set, I think it's the last line the
<Image Source="{Binding Path=Image' ... />
You can just specify the data context for that control.
Edit In reponse to comments
Since you are trying to get the selected item from the combo box and trying to send that over to the image, why not just pass it in as a value into the class that is holding the image.
I think you could do this in xaml but I'm not entirely sure how to do it.

Answer 2

It seems like you're trying to do something like this:
<Page
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sys="clr-namespace:System;assembly=mscorlib">
<DockPanel>
<TextBox DockPanel.Dock="Top" x:Name="Source">x1</TextBox>
<ComboBox DockPanel.Dock="Top" x:Name="myComboBox"
SelectedValue="{Binding ElementName=Source, Path=Text, Mode=TwoWay}">
<sys:String>1</sys:String>
<sys:String>22</sys:String>
<sys:String>333</sys:String>
<sys:String>4444</sys:String>
</ComboBox>
<TextBlock DockPanel.Dock="Top"
Text="{Binding ElementName=myComboBox, Mode=OneWay, Path=SelectedItem.Length}"/>
</DockPanel>
</Page>
The ComboBox is bound to the text of the TextBox using two-way binding, so when you select an item from the ComboBox it updates the TextBox, and when you type a value into the TextBox that's in the ComboBox's list it changes the selected item in the ComboBox.
The TextBlock is bound to a property of the selected item in the ComboBox. Whenever the selected item changes, whether because the user selected a new one or the value in the TextBox changed, the TextBlock gets updated.
But I'm confused by all your talk about data contexts. None of the objects in the example you posted have data contexts.