Why marginBottom isn't working in Spinner?

Question

Could someome explain me why android:layout_marginBottom doesn't work in a Spinner?:

<?xml version="1.0" encoding="utf-8"?>
<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">

    <Spinner
        android:id="@+id/spinner2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginBottom="20dp"/>

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/spinner2" />
</androidx.constraintlayout.widget.ConstraintLayout>

It doesn't matter if I use android:layout_marginBottom or android:layout_margin. However, If I use android:layout_margin it adds top, right and left margin. Why the only margin that does't work is the bottom?

Thanks.

this is relevant https://stackoverflow.com/questions/44931337/applayout-marginbottom-is-not-working-well-with-android-constraint-layout — Zain, Feb 16 '21 at 19:09

score 1 · Answer 1 · answered Feb 16 '21 at 18:35

1

connect constrain from the button to view or parent then it will affect $ app:layout_constraintBottom_toBottomOf="" `

answered Feb 16 '21 at 18:35

Esraa Fathy

28
4

George Sepetadelis · Answer 2 · 2021-02-17T07:48:45.763

1

You need to constraint the spinner to bottom:

1st method: app:layout_constraintBottom_toBottomOf="parent"

2nd method: constraint the spinner to bottom by drag it until the bottom of your root view

edited Feb 17 '21 at 07:48

answered Feb 16 '21 at 18:38

George Sepetadelis

317
1
12

score 1 · Accepted Answer · answered Feb 16 '21 at 19:02

The problem is not about Spinner specifically - if you use two TextViews the behavior stays the same.

Some observations on "why" and "how":

the Spinner top and start is constrained to the top and start of the parent ViewGroup. Since you don't specify a bottom (or end) constraint, a bottom margin is meaningless
the TextView on the other hand has a top constraint - if you let it have a top margin, this will have the desired effect.

Now you could say "well, then I'll just add the bottom constraint to the Spinner". Unfortunately this is not enough (and here I really don't know why the ConstraintLayout solver decides to ignore the margin...)

If you want to set a margin to the Spinner, then the two Views have to belong to a complete vertical chain:

parent top <- Spinner <-> TextView -> parent bottom

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

    <Spinner
        android:id="@+id/spinner2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        android:layout_marginBottom="20dp"
        app:layout_constraintVertical_bias="0"
        app:layout_constraintVertical_chainStyle="packed"/>

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/spinner2"
        app:layout_constraintBottom_toBottomOf="parent"
       />
</androidx.constraintlayout.widget.ConstraintLayout>

Why marginBottom isn't working in Spinner?

3 Answers3