Q:

Android - Make an envelope shape background in xml/vector

I'm trying to do a shape as this one in xml:

It is a simple rectangle, with a solid color and a little transparent triangle in the top-center, from the inner side.
Can this be achieved using vectors?

A:

This is a bit of a hack using ConstraintLayout and a vector drawable, but it works! It will expand to fill the width of its container.
dimens.xml
<dimen name="toolbar_height">200dp</dimen>
<dimen name="toolbar_notch_width">100dp</dimen>

notch.xml
<vector
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="24dp"
    android:height="12dp"
    android:viewportWidth="24"
    android:viewportHeight="12">

    <path
        android:fillColor="#000000"
        android:pathData="m0 0 12 12 12 -12 v12 h-24 v-12 z"/>

</vector>

toolbar.xml
<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="@dimen/toolbar_height"
    tools:layout_gravity="bottom">

    <View
        android:id="@+id/left"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:background="#F44336"
        app:layout_constraintEnd_toStartOf="@id/notch"
        app:layout_constraintStart_toStartOf="parent"/>

    <View
        android:id="@+id/notch"
        android:layout_width="@dimen/toolbar_notch_width"
        android:layout_height="0dp"
        android:background="@drawable/notch"
        android:backgroundTint="#4CAF50"
        app:layout_constraintDimensionRatio="1:0.5"
        app:layout_constraintEnd_toStartOf="@id/right"
        app:layout_constraintStart_toEndOf="@id/left"
        app:layout_constraintTop_toTopOf="parent"/>

    <View
        android:id="@+id/center"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#FFEB3B"
        app:layout_constraintTop_toBottomOf="@id/notch"
        app:layout_constraintStart_toStartOf="@id/notch"
        app:layout_constraintEnd_toEndOf="@id/notch"
        app:layout_constraintBottom_toBottomOf="parent"/>

    <View
        android:id="@+id/right"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:background="#3F51B5"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@id/notch"/>

</androidx.constraintlayout.widget.ConstraintLayout>

Result

