WPF: Customized control focus management - focus

Question

I was tying to set focus on a TextBox used to build a customized "Numeric Up Down" control.
This is the custom "Numeric Up Down"
<Style x:Key="SpinButton" TargetType="Slider" >
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="Slider">
<Border Grid.RowSpan="3" BorderThickness="1,1,1,1" BorderBrush="WhiteSmoke">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width=".5*"/>
<ColumnDefinition Width=".5*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height=".5*"/>
<RowDefinition Height=".5*"/>
</Grid.RowDefinitions>
<TextBox Name="textBoxNumericUpDown" Grid.RowSpan="3" Margin="2,0,0,0" Text="{Binding Value,Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" FontSize="20" VerticalAlignment="Center" Background=" {x:Null}" Foreground="White" BorderThickness="0" CaretBrush="White" IsTabStop="True"/>
<RepeatButton Grid.Column="1" Grid.Row="0" Margin="0,0,-5,0" Command="Slider.IncreaseLarge" Style="{StaticResource TimeRepeatButtonStyle}" Content="+" Background="{x:Null}" BorderBrush="White" Foreground="White" FontSize="18" Cursor="Hand" Width="44" Height="44" IsTabStop="False"/>
<RepeatButton Grid.Column="1" Grid.Row="1" Command="Slider.DecreaseLarge" Margin="0,1,-5,0" Style="{StaticResource TimeRepeatButtonStyle}" Content="-" Background="{x:Null}" BorderBrush="White" Foreground="White" FontSize="18" Cursor="Hand" Width="44" Height="44" IsTabStop="False"/>
</Grid>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Usage
<Slider PreviewTextInput="textBoxTimeMinute_PreviewTextInput" Name="textBoxTimeMinute" Width="100" Style="{StaticResource SpinButton}" Maximum="999" Margin="8" HorizontalAlignment="Left" Minimum="0" IsTabStop="True" TabIndex="0"/>
<Label Grid.Column="1" Content=":" VerticalAlignment="Center" IsTabStop="False"/>
<Slider PreviewTextInput="textBoxTimeSecond_PreviewTextInput" Grid.Column="2" Name="textBoxTimeSecond" Width="100" Style="{StaticResource SpinButton}" Maximum="60" Margin="8" HorizontalAlignment="Left" Minimum="-1" IsTabStop="True" TabIndex="1"/>
Wanted result (Automatic focus on the first textbox if no number inside)
Wanted result (Automatic focus on the first textbox if number inside, number is selected)
I tried different ways to make it select the correct Control, but it always selects the outer layer. In my case The Grid/Border.
Only after I press TAB I can have it select the correct TextBox Control.
Is there any way in WPF I can achieve the focus on textbox without pressing TAB?

Answer 1

Solved:
If you want to focus a TextBox inside a ControlTemplate you have to set up a trigger on the "IsFocused" property.
When it becomes true then you have to set the FocusManager.FocusedElement field to the name of the TextBox (or other control) you want to focus.
Below is the code I used to achieve this:
<ControlTemplate TargetType="Slider">
<TextBox x:Name="TextBoxToFocus"/> //The textbox(or any other element) I want to set focus to. It is very important to have it named, otherwise I won't know which control to focus.
<ControlTemplate.Triggers> //The trigger
<Trigger Property = "IsFocused" Value = "True" /> //The property the trigger is watching
<Setter TargetName="TextBoxToFocus" Property="FocusManager.FocusedElement" Value="{Binding ElementName=NumericUpDown}"/> //Setter when the trigger executes
</Trigger>
</ControlTelmplate.Triggers>