Draw Rectangle View with curve bottom In Android

Just play with the oval item values to get the desired output.

curve_toolbar_bg.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="rectangle"/>
    </item>
    <item
        android:bottom="0dp"
        android:left="-100dp"
        android:right="-100dp"
        android:top="-80dp">
        <shape android:shape="oval">
            <solid android:color="@color/colorPrimary" />
        </shape>
    </item>
</layer-list>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="0dp"
        android:layout_height="?android:attr/actionBarSize"
        android:background="@drawable/curve_toolbar_bg"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0">

    </android.support.v7.widget.Toolbar>
</android.support.constraint.ConstraintLayout>