Android Constraint Layout - Alignment of childrens

问题

So I have a constraint layout with height wrap_content and width match_parent. I would like to know

1. How to align a button to the centre of a recycler view if they are rendered horizontally.

2. How to align a button to the centre of a LinearLayout(which will be populated later).. if they are rendered horizontally.

I tried constraint.Guideline but it seems not working because of constraint layout wrap_content height. any suggestions?

回答1:

Maybe for other people this answer can be useful.

We can have an empty view below recycler view or linear layout.

<View
        android:id="@+id/horizontal_view"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/recyclerview"
        tools:layout_editor_absoluteX="8dp" />

now align button to the centre of parent top and this view.

app:layout_constraintBottom_toTopOf="@+id/horizontal_view"
app:layout_constraintLeft_toLeftOf="@+id/parent"
app:layout_constraintRight_toLeftOf="recyclerview"
app:layout_constraintTop_toTopOf="parent"

This should do the work :)

回答2:

To centre align, you need to set left and right align with respect to parent. e.g.

<Button
    android:id="@+id/button"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"/>

来源：https://stackoverflow.com/questions/46213359/android-constraint-layout-alignment-of-childrens