I have the following custom view:
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<Button
android:id="@+id/declineButton"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toStartOf="@+id/confirmButton"
android:layout_marginTop="0dp"
android:layout_marginBottom="0dp"
android:layout_marginStart="16dp"
android:layout_marginEnd="16dp"
android:text="decline"/>
<Button
android:id="@+id/confirmButton"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="@id/declineButton"
app:layout_constraintBottom_toBottomOf="@id/declineButton"
app:layout_constraintStart_toEndOf="@id/declineButton"
android:layout_marginTop="0dp"
android:layout_marginBottom="0dp"
android:layout_marginEnd="16dp"
android:layout_marginStart="16dp"
android:text="confirm"/>
</androidx.constraintlayout.widget.ConstraintLayout>
In the preview for this layout, the buttons show as expected.
However, if I take that custom view and put it into my activity:
<?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"
android:background="@color/backgroundColor">
<TextView
android:id="@+id/textAbove"
style="@style/someStyle"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintTop_toBottomOf="@id/something"
app:layout_constraintBottom_toTopOf="@id/buttons"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginTop="16dp"
android:layout_marginStart="16dp"
android:layout_marginEnd="16dp"
android:text="text above"/>
<MyCustomButtonsView
android:id="@+id/buttons"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintBottom_toTopOf="@id/textBelow"
app:layout_constraintTop_toBottomOf="@id/textAbove"/>
<TextView
android:id="@+id/textBelow"
style="@style/someStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginBottom="16dp"
android:text="text below"/>
</androidx.constraintlayout.widget.ConstraintLayout>
The buttons do not show in the preview, because the custom view somehow has the height 0:
So, if I add tools:layout_height="80dp"
to MyCustomButtonsView
<MyCustomButtonsView
android:id="@+id/buttons"
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:layout_height="80dp
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintBottom_toTopOf="@id/textBelow"
app:layout_constraintTop_toBottomOf="@id/textAbove"/>
It shows that the buttons themselves are the problem, because the view gets larger, but the buttons still don't show:
The thing is that, if I run the app on my device, the buttons show as expected (without setting a specific hight as in the tools
line).
What I want to know is why this occurs and how to avoid it.
Looks like this was just a glitch in Android Studio. I've rebuilt and restarted before I asked this question and it didn't help. One day later, I open Android Studio and, lo and behold, it shows the buttons properly. So I guess restarting the whole system might be a solution.