Support libraries to add for Autosizing TextViews

Question

I am confused about adding the correct support libraries in Android Studio to be able to use AutoSizing TextViews. https://developer.android.com/guide/topics/ui/look-and-feel/autosizing-textview.html
The description of what support libraries to use is kind of vague on this page. I have tried to import the suggested libraries, but either I am requesting the wrong libraries (they are not found, such as the android.support.v4.widget package) or I am doing something else incorrectly.

My min SDK is 21 and max SDK is 27, so the AutoSizing feature should be backwards compatible for my app if I have the correct libraries imported. However, in the screen design view, I get the warning "Attribute autoSizeTextType is only used in API level 26 and higher (current min is 21)"

As far as I can tell, I have the correct support libraries included. Project Structure Dependencies are as follows:

implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
implementation 'android.arch.lifecycle:compiler:1.0.0'
implementation 'android.arch.persistence.room:runtime:1.0.0'
implementation 'android.arch.persistence.room:compiler:1.0.0'
implementation 'android.arch.paging:runtime:1.0.0-alpha4-1'
implementation 'android.arch.core:core-testing:1.0.0'
implementation 'android.arch.persistence.room:testing:1.0.0'
implementation 'android.arch.lifecycle:common-java8:1.0.0'
implementation 'com.android.support:support-v13:27.0.2'
implementation 'com.android.support:appcompat-v7:27.0.2'
androidTestImplementation 'com.android.support.test:runner:1.0.2-alpha1'
implementation 'com.android.support:support-annotations:27.0.2'
implementation 'com.android.support:support-v4:27.0.2'
implementation 'com.android.support:preference-v14:27.0.2'
implementation 'com.android.support:recyclerview-v7:27.0.2'
implementation 'android.arch.lifecycle:extensions:1.1.0'
implementation 'com.google.android.gms:play-services-location:11.8.0'
implementation 'com.android.support:preference-v7:27.0.0'
implementation 'com.android.support:support-compat:27.0.0'

Any suggestions? I also could use some links on how to convert the suggested libraries to the actual libraries to be imported. Thanks

Edit: partial list of layout with android:autoSizeTextType problem. I get the warning message for both of the textviews listed.

<?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">

<android.support.constraint.Guideline
    android:id="@+id/guideline"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    app:layout_constraintGuide_begin="134dp"/>

<android.support.v7.widget.AppCompatTextView
    android:id="@+id/temperature_label"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginEnd="8dp"
    android:text="@string/temperature"
    android:autoSizeTextType="uniform"
    app:layout_constraintEnd_toStartOf="@+id/guideline"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"/>

<TextView
    android:id="@+id/temperature"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginEnd="8dp"
    android:hint="@string/temperature"
    android:autoSizeTextType="uniform"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintLeft_toRightOf="@+id/guideline"
    app:layout_constraintTop_toTopOf="parent"/>

Edit: My Solution for now.

This layout is what I ended up with that seems to work for now. Not sure if the autoSizing is resizing or not, but this looks good on the devices I am testing for at this time. Tried the plain TextView using the app: prefix for autoSizeTextType as was suggested, but received the error "Unexpected namespace prefix "app" found for tag TextView". When I changed it to android.support.v7.widget.AppCompatTextView, the error went away. Thanks for the help.

<?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">

<android.support.constraint.Guideline
    android:id="@+id/guideline"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    app:layout_constraintGuide_percent="0.38"/>

<android.support.v7.widget.AppCompatTextView
    android:id="@+id/temperature_label"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:text="@string/temperature"
    android:textAppearance="@style/TextAppearance.AppCompat.Large"
    app:autoSizeTextType="uniform"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"/>

<android.support.v7.widget.AppCompatTextView
    android:id="@+id/temperature"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:hint="@string/temperature"
    android:textAppearance="@style/TextAppearance.AppCompat.Large"
    app:autoSizeTextType="uniform"
    app:layout_constraintLeft_toRightOf="@+id/guideline"
    app:layout_constraintTop_toTopOf="parent"/>

Answer 1

Change this:

<android.support.v7.widget.AppCompatTextView
    android:autoSizeTextType="uniform"
    .../>

to this:

<TextView
    app:autoSizeTextType="uniform"
    .../>

There's no need to reference AppCompatTextView directly. The LayoutInflater used by the support library will automatically inject AppCompat widgets in place of standard widgets.

Additionally, to get auto-sizing working pre-API-26, you need to be using the support library implementation, which means you need to be using the AppCompat attributes (with the app: namespace) instead of the platform attributes (with the android: namespace).

Answer 2

Try changing android: to app: namespace :

<android.support.v7.widget.AppCompatTextView
    app:autoSizeTextType="uniform"
    .../>