Problem when trying to wrap chains of width-constrained views

Question

I'm trying to implement a very common portrait/landscape layout flexibility approach using newly-introduced ConstraintLayout Flow helper in chain wrapping mode.

I want to position two views automatically in line for landscape orientation and one under another for portrait, e.g. wrap to fit. I can achieve this already with FlexboxLayout but I prefer a flat structure and performance of ConstraintLayout.

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#B0B0B0">

    <androidx.constraintlayout.helper.widget.Flow
        android:layout_width="0dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:flow_wrapMode="chain"
        app:constraint_referenced_ids="view1,view2"
        android:layout_height="0dp" />

    <View
        android:id="@+id/view1"
        android:layout_width="0dp"
        android:layout_height="200dp"
        app:layout_constraintDimensionRatio="1:1"
        android:background="#808080"
        tools:ignore="MissingConstraints">
    </View>

    <View
        android:id="@+id/view2"
        android:layout_width="0dp"
        android:layout_height="200dp"
        app:layout_constraintDimensionRatio="1:1"
        android:background="#E0E0E0"
        tools:ignore="MissingConstraints">
    </View>

</androidx.constraintlayout.widget.ConstraintLayout>

I get this for landscape, and it's fine:

But I get this for portrait:

If I set fixed width 200dp (or wrap_content for other cases also ok), everything works as expected:

Since ConstraintLayout 2.0.0 is in beta and recent changelog reports about fixes in wrap support, I suppose that it is a bug.

But maybe I'm missing something? Thank you

Answer 1

The default orientation of the Flow widget is horizontal. Therefore, it needs to know layout_width values of its referenced widgets.

It seems that Flow can't calculate these values based on the app:layout_constraintDimensionRatio (at least, not in the Tools preview.. I did not test how it behaves at runtime).

In your code, you can swap the layout_width and layout_height values to achieve your desired results.

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:ignore="MissingConstraints">

    <androidx.constraintlayout.helper.widget.Flow
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:constraint_referenced_ids="view_red, view_blue"
        app:flow_wrapMode="chain"/>

    <View
        android:id="@+id/view_red"
        android:layout_width="300dp"
        android:layout_height="0dp"
        android:background="#C62828"
        app:layout_constraintDimensionRatio="1:1"/>

    <View
        android:id="@+id/view_blue"
        android:layout_width="300dp"
        android:layout_height="0dp"
        android:background="#1565C0"
        app:layout_constraintDimensionRatio="1:1"/>

</androidx.constraintlayout.widget.ConstraintLayout>

However, keep in mind that chaining/wrapping only occurs if the referenced widgets do not fit in the specified orientation (default: horizontal). In my code, I had to set layout_width to 300dp for chaining to happen in the Tools preview.

So, if you're running on a tablet, for example, using this method will not guarantee that your widgets will be positioned vertically because there is more horizontal space to accommodate the widgets.