使用 <include>与<合并>在约束布局中 [英] Using <include> with <merge> in ConstraintLayout

问题描述

我在 ConstraintLayout 中使用标签 和 时遇到问题.

我想创建一个平面视图层次结构(因此是约束)，但仍然具有可重用的元素.所以我在我的布局中使用 并在包含的布局中使用 以避免嵌套布局(尤其是避免嵌套的 ConstraintLayouts)

所以我写了这个:父布局

相反，我得到了这个
很明显，我放在  标签中的约束被包含的布局中的约束覆盖.
这是预期的行为吗?如果是，我们应该如何使用  和 ConstraintLayout 保持平面布局?
解决方案
简短回答
最好的做法是用(嵌套的)ConstraintLayout 替换  块，而不是使用冗余布局结构.>


<块引用>
ConstraintLayout 很棒，但它不适用于组合以及每个部分的职责分离
这是错误的.ConstraintLayout 在重用布局方面效果很好. 任何根据兄弟视图和父布局之间的关系对所有子视图进行布局的布局，其行为都与此完全相同.即使对于 RelativeLayout 也是如此.

那么，问题出在哪里?
让我们仔细看看<merge> 是.
医生说
<块引用>
 标签有助于消除视图中的冗余视图组将一种布局包含在另一种布局中时的层次结构.
它与用  块的内容替换  元素具有相同的效果.换句话说， 块中的视图直接放置到父布局中，没有中间视图组.因此，完全忽略  元素的约束.
在这个特定的例子中，包含布局中的视图被添加到父级两次，作为第二个在另一个之上.

结论
布局资源文件旨在独立使用.为了限定术语可重用，它不应依赖于它的父级(将来将添加到其中的视图组).如果您只需要包含一次布局，那看起来还不错.但是 </merge> 在这种情况下也不是一个好主意，因为你不能将它放在任何不同布局的不同位置.
显然，平面布局层次结构具有更好的性能.然而，有时我们可能不得不牺牲它.
I am having trouble using tags <include> and <merge> inside a ConstraintLayout. 

I want to create a flat view hierarchy (hence Constraints) but still have elements that are reusable. So I use <include> in my layout and <merge> in the included layouts to avoid having nested layouts (especially avoiding nested ConstraintLayouts)

So I wrote this:
Parent layout
<android.support.constraint.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <include
        android:id="@+id/review_1"
        layout="@layout/view_movie_note"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/review_2"/>

    <include
        layout="@layout/view_movie_note"
        android:id="@+id/review_2"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginLeft="7dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toRightOf="@+id/review_1"
        app:layout_constraintRight_toRightOf="parent"
        />

</android.support.constraint.ConstraintLayout>
and this view_movie_note : 
<merge>

    <TextView
        android:id="@+id/note_origin"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="15dp"
        android:layout_marginStart="5dp"
        app:layout_constraintStart_toStartOf="@+id/cardView2"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginLeft="5dp" />


    <android.support.v7.widget.CardView
        android:id="@+id/five_star_view_container"
        android:layout_width="0dp"
        android:layout_height="52dp"
        android:layout_marginBottom="8dp"
        android:layout_marginTop="10dp"
        android:elevation="3dp"
        app:cardUseCompatPadding="true"
        app:contentPaddingTop="22dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHeight_min="52dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/note_origin">

        <FiveStarsView
            android:id="@+id/five_star_view"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal" />

    </android.support.v7.widget.CardView>

    <android.support.v7.widget.CardView
        android:id="@+id/cardView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        app:cardBackgroundColor="@color/colorPrimary"
        app:contentPaddingLeft="15dp"
        app:contentPaddingRight="15dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/note_origin">

        <TextView
            android:id="@+id/grade"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="12sp" />

    </android.support.v7.widget.CardView>


</merge>
I am expecting this



Instead I got this



Clearly the constraints that I put in the <include> tag are overriden by the constraints in the included layout. 

Is this the expected behaviour ? If yes, how are we supposed to keep a flat layout using <include> and ConstraintLayout ?
解决方案
Short answer

The best move will be replacing <merge> block with a (nested) ConstraintLayout rather than using redundant layout structure.






  
ConstraintLayout is great but it doesn't work well with composition
  and separation of responsibilities of each piece
That is wrong. ConstraintLayout does work well with reusing layouts. Any layout in which all child views are laid out according to relationships between sibling views and the parent layout, behaves exactly like this. This is true even for RelativeLayout.




Then, where is the problem?

Let's take a closer look at what <merge> is.

The doc says 

  
The <merge/> tag helps eliminate redundant view groups in your view
  hierarchy when including one layout within another.
It will have the same effect as replacing the <include> element with the contents of <merge> block. In other words, the views in the <merge/> block is directly placed to the parent layout without an intermediate view group. Therefore, the constraints of the <include> element is completely ignored.

In this particular example, the views in the including layout is added two times to the parent as the second one on top of another.




Conclusion

Layout resource files are intended to be used independently. To qualify the term reusable, it should not depend on it's parent (The view group in which it will be added in future). 
It would be looking okay if you had to include the layout only one time. But </merge> won't be a good idea in that case too because you can't place it in any different layout in a different position.

Obviously, flat layout hierarchies have better performance. However, sometimes we may have to sacrifice it.

                        
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