Change app wide font-size using a theme for Android

Question

Is it possible to make every bit of text larger on an Android application, mimicking what happens when you change the default font size in the global settings screen? I want for the user to select a font size in the settings screen and all of the text to change, without needing to put extra style tags onto my individual screens.

I have three themes so far which correctly change the font size for TextView's but not things like EditText, or ListView elements

<style name="AppThemeSmall" parent="AppTheme">
    <item name="android:textViewStyle">@android:style/TextAppearance.Small</item>
    <item name="android:textAppearance">@android:style/TextAppearance.Small</item>
</style>

<style name="AppThemeMedium" parent="AppTheme">
    <item name="android:textViewStyle">@android:style/TextAppearance.Medium</item>
    <item name="android:textAppearance">@android:style/TextAppearance.Medium</item>
</style>

<style name="AppThemeLarge" parent="AppTheme">
    <item name="android:textViewStyle">@android:style/TextAppearance.Large</item>
    <item name="android:textAppearance">@android:style/TextAppearance.Large</item>
</style>

Answer 1

I ended up adding styles to the xml, it felt cleaner that way and I had more control.

each layout xml (inc. EditText, AutoCompleteTextView)

 <TextView
   style="?textTitle"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:text="@string/ref" />

attrs.xml

<attr name="textTitle" format="reference" />

styles.xml (note that I've overridden the spinner style as well to keep the sizes consistent

<style name="AppTheme.Small">
    <item name="textTitle">@style/small_title_text</item>
    <item name="android:spinnerItemStyle">@style/spinner_small</item>
</style>

<style name="AppTheme.Medium">
    <item name="textTitle">@style/medium_title_text</item>
    <item name="android:spinnerItemStyle">@style/spinner_medium</item>
</style>

<style name="AppTheme.Large">
    <item name="textTitle">@style/large_title_text</item>
    <item name="android:spinnerItemStyle">@style/spinner_large</item>
</style>


<!-- SMALL FONT SIZE -->
<style name="small_title_text">
    <item name="android:textSize">15sp</item>
    <item name="android:textStyle">bold</item>
</style>


<!-- MEDIUM FONT SIZE -->
<style name="medium_title_text">
    <item name="android:textSize">19sp</item>
    <item name="android:textStyle">bold</item>
</style>

<style name="medium_list_text"></style>

<!-- LARGE FONT SIZE -->
<style name="large_title_text">
    <item name="android:textSize">23sp</item>
    <item name="android:textStyle">bold</item>
</style>

<style name="large_list_text"></style>

<!-- SPINNER STYLES -->
<style name="spinner_small">
    <item name="android:textSize">17sp</item>
    <item name="android:paddingTop">0dip</item>
</style>

<style name="spinner_medium">
    <item name="android:textSize">21sp</item>
    <item name="android:paddingTop">0dip</item>
</style>

<style name="spinner_large">
    <item name="android:textSize">25sp</item>
    <item name="android:paddingTop">0dip</item>
</style>

Then I set the theme before every activity is created.

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    PreferenceHelper mPrefs = PreferenceHelper.getInstance(this);
    setTheme(mPrefs.getTheme());
    setContentView(R.layout.activity_list);