What are the differences between R.styleable, R.style and R.attr?

Question

What are the differences between R.styleable, R.style and R.attr? I found TextAppearance in all of these three classes.

Answer 1

R.style has all styles android provided (including all Theme android provided). E.g., Theme.Translucent, Widget.AbsListView.

R.attr has all attrs android provided (that could be set to view or window). E.g., layout_width can be set to view, windowIsFloating can be set to window.

R.styleable has all attrs of a specific view or window that android provided AND can be defined in a style. E.g., FrameLayout_Layout_layout_gravity: layout_gravity can be styled for FrameLayout, Window_windowIsFloating: Flag indicating whether this is a floating window.

To answer your question, TextAppearance is a attribute (R.attr) AND it is declared styleable, attrs.xml:

<attr name="textAppearance" format="reference" />
<declare-styleable name="TextViewAppearance">
     <!-- Base text color, typeface, size, and style. -->
     <attr name="textAppearance" />
</declare-styleable>

TextAppearance is also a Theme/ Style (Theme is just a style), styles.xml:

<style name="TextAppearance">
    <item name="android:textColor">?textColorPrimary</item>
    <item name="android:textColorHighlight">?textColorHighlight</item>
    <item name="android:textColorHint">?textColorHint</item>
    <item name="android:textColorLink">?textColorLink</item>
    <item name="android:textSize">16sp</item>
    <item name="android:textStyle">normal</item>
</style>

Just in case you don't understand what the "?" means, check: Question mark (?) in XML attributes for Android And in case you are puzzled by what is declare-styleable, check: Difference between declare-styleable and style