What does 'view' container do in XML of Android

Question

In this XML what is advantage of using view?

    <?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout android:id="@+id/coordinatorLayout2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:id="@+id/constraintLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <View
                android:id="@+id/view"
                android:layout_width="100dp"
                android:layout_height="720dp"
                android:layout_marginStart="8dp"
                android:layout_marginEnd="8dp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <Button
                android:id="@+id/toggleBtn"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="72dp"
                android:text="@string/toggle_screen"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <TextView
                android:id="@+id/textTv"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="120dp"
                android:text="@string/primary_screen"
                android:textSize="18sp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="@+id/toggleBtn"
                app:layout_constraintStart_toStartOf="@+id/toggleBtn"
                app:layout_constraintTop_toBottomOf="@+id/toggleBtn" />

        </androidx.constraintlayout.widget.ConstraintLayout>

    </androidx.coordinatorlayout.widget.CoordinatorLayout>

I tested the code with and without view and I didn't see any difference in its output on device. Generally what is usage of view in XML? Thanks for any help.

Answer 1

According to your layout, I've just updated your layout added colour to see the view, below is the layout and image.

Here is your layout:

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout android:id="@+id/coordinatorLayout2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/constraintLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <View
            android:id="@+id/view"
            android:layout_width="100dp"
            android:layout_height="720dp"
            android:layout_marginStart="8dp"
            android:layout_marginEnd="8dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            android:background="@color/black_2"/>

        <Button
            android:id="@+id/toggleBtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="72dp"
            android:text="this is button"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/textTv"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="120dp"
            android:text="this is text view"
            android:textSize="18sp"
            android:textStyle="bold"
            app:layout_constraintEnd_toEndOf="@+id/toggleBtn"
            app:layout_constraintStart_toStartOf="@+id/toggleBtn"
            app:layout_constraintTop_toBottomOf="@+id/toggleBtn" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

Image with view

So, if you have view, because of the height of ConstraintLayout is 720dp the ConstraintLayout will stretch to maximum because of wrap_content behaviour.

Height of Constraint Layout with View

And if you remove view, then the height of ConstraintLayout also changes

Height of Constraint Layout without View

It depends on your requirement, you need to have View or not, but currently it has no impact.