构造函数，它是Object类的一部分(Constructor which is a part of Object class)

 把拼图的各个部分拼凑在一起 
 
 AdornerLayer表示用于渲染装饰者的表面。 由于AdornerLayer通常提供整个视图，而不仅仅是一个控件，因此默认情况下某些容器会实现它们。 
 
 装饰器是绑定到UIElement的自定义FrameworkElement 。 Adorner在AdornerLayer中呈现， AdornerLayer是一个始终位于装饰元素或装饰元素集合之上的渲染表面。 
 
 因此，在这种情况下，adorner（红色矩形）绑定到TextBox ，但是在TextBox顶部的图层中呈现。 
 
 通过调用静态方法GetAdornerLayer来获取装饰的UIElement的AdornerLayer对象来完成装饰（例如，在验证错误的情况下）。 
 
 足够的理论 
 
 更改TabItems会丢弃AdornerLayer ，导致不会绘制装饰器。 2个修复： 
 
 \手动方式，由DRapp提出： 
 
<XAML for MyView1>
   <AdornerDecorator>
      ...
   </AdornerDecorator>
</close XAML for MyView1>
 
 当然，如果在AdornerDecorator和TextBox （在可视化树中）有另一个容器实现AdornerLayer ，这将没有任何好处。 因此显式的AdornerDecorator需要是包装TextBox的最后一个。 
 
<XAML for MyView1>
    <Grid>

        ...

        <GroupBox>
            <AdornerDecorator>
                <Grid>

                    ...

                    <TextBox ... />
                </Grid>
            </AdornerDecorator>
        </GroupBox>
    </Grid>
</close XAML for MyView1>
 
 \第二个解决方案（我更喜欢）每次TextBox变得可见时重置ErrorTemplate 。 这样做可以发现并修复AdornerLayer的缺失。 
 
<UserControl.Resources>
    <Style TargetType="{x:Type TextBox}">
        <Style.Triggers>
            <Trigger Property="IsVisible" Value="true">
                <Setter Property="Validation.ErrorTemplate">
                    <Setter.Value>
                        <ControlTemplate>
                            <Border BorderBrush="Red" BorderThickness="1">
                                <AdornedElementPlaceholder/>
                            </Border>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Trigger>
        </Style.Triggers>
    </Style>
</UserControl.Resources>

Putting together the pieces of the puzzle
 
An AdornerLayer represents a surface for rendering adorners. As an AdornerLayer usually serves an entire view, not just one control, some containers implement them by default.
 
An adorner is a custom FrameworkElement that is bound to a UIElement. Adorners are rendered in an AdornerLayer, which is a rendering surface that is always on top of the adorned element or a collection of adorned elements.
 
So in this case the adorner (red rectangle) is bound to a TextBox, but is rendered in a layer on top of the TextBox.
 
Adorning (e.g. in case of a validation error) is done by calling the static method GetAdornerLayer to get an AdornerLayer object for the UIElement to be adorned.
 
Enough theory
 
Changing TabItems discards the AdornerLayer, resulting in the adorner not being drawn. 2 fixes:
 
\The manual way, as proposed by DRapp:
 
<XAML for MyView1>
   <AdornerDecorator>
      ...
   </AdornerDecorator>
</close XAML for MyView1>
 
Of course, if there's another container implementing an AdornerLayer between the AdornerDecorator and the TextBox (in the visual tree), this won't do any good. So the explicit AdornerDecorator needs to be the last one wrapping the TextBox.
 
<XAML for MyView1>
    <Grid>

        ...

        <GroupBox>
            <AdornerDecorator>
                <Grid>

                    ...

                    <TextBox ... />
                </Grid>
            </AdornerDecorator>
        </GroupBox>
    </Grid>
</close XAML for MyView1>
 
\Second solution (which I prefer) resetting the ErrorTemplate each time the TextBox becomes visible. In doing so the lack of AdornerLayer gets spotted and fixed.
 
<UserControl.Resources>
    <Style TargetType="{x:Type TextBox}">
        <Style.Triggers>
            <Trigger Property="IsVisible" Value="true">
                <Setter Property="Validation.ErrorTemplate">
                    <Setter.Value>
                        <ControlTemplate>
                            <Border BorderBrush="Red" BorderThickness="1">
                                <AdornedElementPlaceholder/>
                            </Border>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Trigger>
        </Style.Triggers>
    </Style>
</UserControl.Resources>