Focus to a specific editable datagrid cell in wpf DataGrid on RowSelection - mvvm

Question

I have four columns in a datagrid and fourth column is templated and has textbox which is always editable.
What i am trying to achieve here is when a row selection changes the highlighted row's fourth cell which is editable and has textbox in it should get focus.
I am ok to get this done in codebehind or xaml.
Here is what i did:
<DataGrid Name="MyGrid" SelectionChanged="MyGrid_OnSelectionChanged" AutoGenerateColumns="False">
<DataGrid.Columns>
<DataGridTextColumn Binding="{Binding Str1}" IsReadOnly="True"/>
<DataGridTextColumn Binding="{Binding Str2}" IsReadOnly="True"/>
<DataGridTextColumn Binding="{Binding Str3}" IsReadOnly="True"/>
<DataGridTemplateColumn >
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBox Text="{Binding Str4}" GotFocus="UIElement_OnGotFocus" >
<TextBox.Style >
<Style TargetType="TextBox">
<Style.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource AncestorType=DataGridCell,AncestorLevel=1},Path=IsSelected}">
<Setter Property="FocusManager.FocusedElement" Value="{Binding RelativeSource={RelativeSource Self}}"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
</DataGrid.Columns>
</DataGrid>
private void PopulateDummies()
{
int i = 0;
List<SomeDummy> dummies = new List<SomeDummy>();
while (i < 10)
{
dummies.Add(new SomeDummy
{
Str1 = string.Format("Str1:{0}", i),
Str2 = string.Format("Str2:{0}", i),
Str3 = string.Format("Str3:{0}", i),
Str4 = string.Format("Str4:{0}", i)
});
i++;
}
MyGrid.ItemsSource = dummies;
}
private void MyGrid_OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
}
private void UIElement_OnGotFocus(object sender, RoutedEventArgs e)
{
var txtB = sender as TextBox;
txtB.Focus();
txtB.SelectAll();
}
Nothing seems to work. Not sure what is the reason. Can anyone help

Answer 1

The statement
txtB.Focus();
effectively replaces the DataGridCell by a TextEditory control. In order to do this, the view needs to be updated and therefore the UI-tread needs to run.
The SelectAll can not run until the editor is created, so run it as a separate Dispatcher-job and replace it with the following:
Application.Current.Dispatcher.BeginInvoke(new Action(() => {
txtB.SelectAll();
}), DispatcherPriority.Render);
This will do the trick and you don't need the SelctionChanged-event handler for this purpose.