Wpf ToolTip 绑订

<TextBlock Name="Block" Text="1111">
                <TextBlock.ToolTip>
                    <ToolTip DataContext="{Binding PlacmentTarget,RelativeSource={RelativeSource Self}}">
                        <TextBox Text="{Binding Text}"></TextBox>
                    </ToolTip>
                </TextBlock.ToolTip>
            </TextBlock>