Resources in Android

Application resources are stored under the res/ folder of your project hierarchy. In this folder, each of the available resource types can have a subfolder containing its resources.

There are seven primary resource types that have different folders: simple values, drawables, layouts, animations, XML, styles, and raw resources.

This process also creates an R class file that contains references to each of the resources you include in your project. This lets you reference the resources in your code, with the advantage of design time syntax checking.

In all cases, the resource file-names should contain only lowercase letters, numbers, and the period (.) and underscore (_) symbols.

1) Simple Values:
Supported simple values include strings, colors, dimensions, and string or integer arrays. All simple values are stored within XML files in the res/values folder.

<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">To Do List</string>
<color name="app_background">#FF0000FF</color>
<dimen name="default_border">5px</dimen>
<array name="string_array">
<item>Item 1</item>
<item>Item 2</item>
<item>Item 3</item>
</array>
<array name="integer_array">
<item>3</item>
<item>2</item>
<item>1</item>
</array>
</resources>


Dimensions are most commonly referenced within style and layout resources. They’re useful for creating layout constants such as borders and font heights. To specify a dimension resource use the <dimen> tag, specifying the dimension value, followed by an identifier describing the scale of your dimension:

px (screen pixels), in (physical inches), pt (physical points), mm (physical millimeters), dp (density-independent pixels relative to a 160-dpi screen), sp (scale-independent pixels)

Styles and Themes:
Style resources let your applications maintain a consistent look and feel by enabling you to specify the
attribute values used by Views. The most common use of themes and styles is to store the colors and
fonts for an application.

<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="BaseText">
<item name="android:textSize">14sp</item>
<item name="android:textColor">#111</item>
</style>
<style name="SmallText" parent="BaseText">
<item name="android:textSize">8sp</item>
</style>
</resources>

Drawables:
Drawable resources include bitmaps and NinePatch (stretchable PNG) images. They also include complex composite Drawables, such as LevelListDrawables and StateListDrawables that can be defined in XML. 


Layouts:
Layout resources let you decouple your presentation layer by designing user interface layouts in XML rather than constructing them in code. The most common use of a layout is for defining the user interface for an Activity. Once defined in XML, the layout is ‘‘inflated’’ within an Activity using setContentView, usually within the onCreate method.


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello World!"/>
</LinearLayout>


Animations:
Android supports two types of animation. Tweened animations can be used to rotate, move, stretch and fade a View; or you can create frame-by-frame animations to display a sequence of Drawable images.

Tweened animation is stored in a separate XML file in the project’s res/anim folder. An animation can be defined for changes in alpha (fading), scale (scaling), translate (movement), or rotate (rotation).

Frame-by-frame animations let you create a sequence of Drawables, each of which will be displayed for a specified duration, on the background of a View.

Menus:
Create menu resources to further decouple your presentation layer by designing your menu layouts in XML rather than constructing them in code. Menu resources can be used to define both Activity and context menus within your applications, and provide the same options you would have when constructing your menus in code. Once defined in XML, a menu is ‘‘inflated’’ within your application via the inflate method of the MenuInflator Service, usually within the onCreateOptionsMenu method.