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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="co.prandroid.autosizingtextview.MainActivity">

    <TextView
        android:id="@+id/textview"
        android:layout_width="match_parent"
        android:layout_height="20dp"
        android:textSize="12sp"
        android:text="Hello World!,This is PrAndroid"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:autoSizeTextType="uniform"
        android:autoSizeMinTextSize="12sp"
        android:autoSizeMaxTextSize="100sp"
        android:autoSizeStepGranularity="2sp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintVertical_bias="0.038"
        android:layout_marginTop="8dp" />

    <TextView
        android:id="@+id/textview1"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:textSize="24sp"
        android:text="Hello World!,This is PrAndroid"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:autoSizeTextType="uniform"
        android:autoSizeMinTextSize="12sp"
        android:autoSizeMaxTextSize="100sp"
        android:autoSizeStepGranularity="2sp"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintVertical_bias="0.0"
        android:layout_marginTop="8dp"
        app:layout_constraintTop_toBottomOf="@+id/textview" />
    <TextView
        android:id="@+id/textview2"
        android:layout_width="match_parent"
        android:layout_height="120dp"
        android:textSize="36sp"
        android:text="Hello World!,This is PrAndroid"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:autoSizeTextType="uniform"
        android:autoSizePresetSizes="@array/autosize_text_sizes"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintVertical_bias="0.046"
        android:layout_marginTop="8dp"
        app:layout_constraintTop_toBottomOf="@+id/textview1" />


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        tools:ignore="MissingConstraints"
        android:layout_marginTop="8dp"
        app:layout_constraintTop_toBottomOf="@+id/textview2">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="140dp"
            android:textSize="40sp"
            android:background="@mipmap/ic_launcher_foreground"
            android:text="Hello World!,This is PrAndroid"
            android:autoSizeTextType="uniform"
            android:autoSizePresetSizes="@array/autosize_text_sizes" />
    </LinearLayout>

</android.support.constraint.ConstraintLayout>