wpf combobox with not focused empty text

Question

I'm using framework 4.0.

How to display grayed text in editable combobox when it is empty and not focused like in picture

Answer 1

UPDATE:

There is no direct way to implement in WPF except using a TextBlock and ComboBox and laying them over each other.

<Grid HorizontalAlignment="Left" Height="21.545" VerticalAlignment="Top" Width="120.964" Margin="56.958,108.962,0,0">
        <ComboBox IsEditable="True" Name="myComboBox" HorizontalAlignment="Left" VerticalAlignment="Top" Width="120">
            <!--Items Here-->
        </ComboBox>
        <TextBlock Text="Please Select" IsHitTestVisible="False" Foreground="Gray" x:Name="textBlock" HorizontalAlignment="Left" TextWrapping="Wrap" Margin="3.993,2.664,0,0">
            <TextBlock.Style>
                <Style TargetType="TextBlock">
                    <Style.Setters>
                        <Setter Property="Visibility" Value="Hidden" />
                    </Style.Setters>
                    <Style.Triggers>
                        <MultiDataTrigger>
                            <MultiDataTrigger.Conditions>
                                <Condition Binding="{Binding Text, ElementName=myComboBox, Mode=OneWay}" Value=""/>
                                <Condition Binding="{Binding IsKeyboardFocusWithin, ElementName=myComboBox, Mode=OneWay}" Value="False" />
                            </MultiDataTrigger.Conditions>
                            <MultiDataTrigger.Setters>
                                <Setter Property="Visibility" Value="Visible" />
                            </MultiDataTrigger.Setters>
                        </MultiDataTrigger>
                    </Style.Triggers>
                </Style>
            </TextBlock.Style>
        </TextBlock>
    </Grid>

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Sorry about this. I misunderstood the question previously. This answer is for UWP.

I think placeholder text is what you are looking for. Check this out ComboBox.PlaceholderText property in MSDN Docs.