Inform It: December 2016

Any Android project contain things such as application source code and resource files. Some are generated for you by default, while others should be created if required. Lets have a look at android eclipse project directory structure below :

src

User specified java source code files will be available here.

gen

The gen directory in an Android project contains auto generated files. You can see R.java inside this folder which is a generated class which contains references to certain resources of the project. R.java is automatically created by the Eclipse IDE and any manual changes are not necessary

res

Android supports resources like images and certain XML configuration files, these can be keep separate from the source code. All these resources should be placed inside the res folder. This res folder will be having sub-folders to keep the resources based on its type.

/res/values

Used to define strings, colors, dimensions, styles and static arrays of strings or integers. By convention each type is stored in a separate file, e.g. strings are defined in the

/res/animator

This folder contains animations in XML for the property animation API which allows to animate arbitrary properties of objects over time

/res/layout

This folder contains the layouts to be used in the application.A layout resource defines the architecture for the UI in an Activity or a component of a UI. These are resource directories in an application that provides different layout designs for different screen sizes

/res/layout - layout for normal screen size or default

/res/layout-small - layout for small screen size

/res/layout-large - layout for large screen size

/res/layout-xlarge -layout for extra-large screen size

/res/layout-xlarge-land - layout for extra-large in landscape orientation

/res/layout-sw600dp - layout for tablets or layout for 7” tablets (600dp wide and bigger)

/res/layout-sw720dp - layout for 10” tablets (720dp wide and bigger)

/res/layout-w600dp - layout for Multi-pane (any screen with 600dp available width or more)

/res/menu

menu resources to be used in the application (Options Menu, Context Menu, or submenu)

/res/raw

This folder contains raw resources that can be looked up by their resource IDs. These resources can be referenced from other resources all of the same way we do with other resources.

/res/drawable

Drawable folders are resource directories in an application that provides different l bitmap drawables for medium, high, and extra high density screens.

/res/drawable-mdpi - bitmap for medium density

/res/drawable-hdpi - bitmap for high density

/res/drawable-xhdpi - bitmap for extra high density

/res/drawable-nodpi - bitmap with no pre-scaling

libs

External library files will be placed in this folder. If you want to any external library in your project place the library jar inside this folder and it will be added to the classpath automatically.

assets

bin

Bin folder is the area used by the compiler to prepare the files to be finally packaged to the application’s APK file. This includes

Compiling your Java code into class files

Putting your resources (including images) into a structure to be zipped into the APK

This is the output directory of the build. This is where you can find the final .apk file and other compiled resources.

AndroidManifest.xml

All the android applications will have an AndroidManifest.xml file in the root directory. This file will contain essential information about the application to the Android system, information the system must have before it can run any of the application's code. This control file describes the nature of the application and each of its components

ic_launcher-web.png

This is an icon to be used in Google play. Applications on Google Play require a high fidelity version of the application icon. It is not used in your actual app or the launcher, so it is not packaged in the APK.. The specifications for the high-resolution icon are:

32-bit PNG with an alpha channel

512 x 512 pixels

Maximum size of 1024KB

proguard-project.txt

Everything in the proguard-project.txt file will be in commented out state, because in general most people don't have any project specific needs, just to run ProGuard tool with standard settings.

The ProGuard tool shrinks, optimizes, and obfuscates your code by removing unused code and renaming classes, fields, and methods with semantically obscure names. The result is a smaller sized .apk file that is more difficult to reverse engineer.

project.properties

project.properties is the main project’s properties file containing information such as the build platform target and the library dependencies has been renamed from default.properties in older SDK versions. This file is integral to the project.

There are many more items which you use to build a good Android application. Apart from coding for the application, you take care of various other resources like static content that your code uses, such as bitmaps, colors, layout definitions, user interface strings, animation instructions, and more. These resources are always maintained separately in various sub-directories under res/ directory of the project.

This tutorial will explain you how you can organize your application resources, specify alternative resources and access them in your applications.

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Animation Resources

Define pre-determined animations.
Tween animations are saved in res/anim/ and accessed from the R.anim class.
Frame animations are saved in res/drawable/ and accessed from the R.drawable class.

Color State List Resource

Define a color resources that changes based on the View state.
Saved in res/color/ and accessed from the R.color class.

Drawable Resources

Define various graphics with bitmaps or XML.
Saved in res/drawable/ and accessed from the R.drawable class.

Layout Resource

Define the layout for your application UI.
Saved in res/layout/ and accessed from the R.layout class.

Menu Resource

Define the contents of your application menus.
Saved in res/menu/ and accessed from the R.menu class.

String Resources

Define strings, string arrays, and plurals (and include string formatting and styling).
Saved in res/values/ and accessed from the R.string, R.array, and R.plurals classes.

Style Resource

Define the look and format for UI elements.
Saved in res/values/ and accessed from the R.style class.

Bool: XML resource that carries a boolean value.
Color: XML resource that carries a color value (a hexadecimal color).
Dimension: XML resource that carries a dimension value (with a unit of measure).
ID: XML resource that provides a unique identifier for application resources and components.
Integer: XML resource that carries an integer value.
Integer Array: XML resource that provides an array of integers.
Typed Array: XML resource that provides a TypedArray (which you can use for an array of drawables).

Bool

A boolean value defined in XML.

Note: A bool is a simple resource that is referenced using the value provided in the name attribute (not the name of the XML file). As such, you can combine bool resources with other simple resources in the one XML file, under one <resources> element.

FILE LOCATION:

res/values/filename.xml
The filename is arbitrary. The <bool> element's name will be used as the resource ID.

RESOURCE REFERENCE:

In Java: R.bool.bool_name
In XML: @[package:]bool/bool_name

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <bool
        name="bool_name"
        >[true | false]</bool>
</resources>

ELEMENTS:

EXAMPLE:

XML file saved at res/values-small/bools.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <bool name="screen_small">true</bool>
    <bool name="adjust_view_bounds">true</bool>
</resources>

This application code retrieves the boolean:

Resources res = getResources();
boolean screenIsSmall = res.getBoolean(R.bool.screen_small);

This layout XML uses the boolean for an attribute:

<ImageView
    android:layout_height="fill_parent"
    android:layout_width="fill_parent"
    android:src="@drawable/logo"
    android:adjustViewBounds="@bool/adjust_view_bounds" />

Color

A color value defined in XML. The color is specified with an RGB value and alpha channel. You can use a color resource any place that accepts a hexadecimal color value. You can also use a color resource when a drawable resource is expected in XML (for example, android:drawable="@color/green").

The value always begins with a pound (#) character and then followed by the Alpha-Red-Green-Blue information in one of the following formats:

#RGB
#ARGB
#RRGGBB
#AARRGGBB

Note: A color is a simple resource that is referenced using the value provided in the name attribute (not the name of the XML file). As such, you can combine color resources with other simple resources in the one XML file, under one <resources> element.

FILE LOCATION:

res/values/colors.xml
The filename is arbitrary. The <color> element's name will be used as the resource ID.

RESOURCE REFERENCE:

In Java: R.color.color_name
In XML: @[package:]color/color_name

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color
        name="color_name"
        >hex_color</color>
</resources>

ELEMENTS:

EXAMPLE:

XML file saved at res/values/colors.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <color name="opaque_red">#f00</color>
   <color name="translucent_red">#80ff0000</color>
</resources>

This application code retrieves the color resource:

Resources res = getResources();
int color = res.getColor(R.color.opaque_red);

This layout XML applies the color to an attribute:

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:textColor="@color/translucent_red"
    android:text="Hello"/>

Dimension

A dimension value defined in XML. A dimension is specified with a number followed by a unit of measure. For example: 10px, 2in, 5sp. The following units of measure are supported by Android:

dp: Density-independent Pixels - An abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi (dots per inch) screen, on which 1dp is roughly equal to 1px. When running on a higher density screen, the number of pixels used to draw 1dp is scaled up by a factor appropriate for the screen's dpi. Likewise, when on a lower density screen, the number of pixels used for 1dp is scaled down. The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion. Using dp units (instead of px units) is a simple solution to making the view dimensions in your layout resize properly for different screen densities. In other words, it provides consistency for the real-world sizes of your UI elements across different devices.
sp: Scale-independent Pixels - This is like the dp unit, but it is also scaled by the user's font size preference. It is recommend you use this unit when specifying font sizes, so they will be adjusted for both the screen density and the user's preference.
pt: Points - 1/72 of an inch based on the physical size of the screen, assuming a 72dpi density screen.
px: Pixels - Corresponds to actual pixels on the screen. This unit of measure is not recommended because the actual representation can vary across devices; each devices may have a different number of pixels per inch and may have more or fewer total pixels available on the screen.
mm: Millimeters - Based on the physical size of the screen.
in: Inches - Based on the physical size of the screen.

Note: A dimension is a simple resource that is referenced using the value provided in the name attribute (not the name of the XML file). As such, you can combine dimension resources with other simple resources in the one XML file, under one <resources> element.

FILE LOCATION:

res/values/filename.xml
The filename is arbitrary. The <dimen> element's name will be used as the resource ID.

RESOURCE REFERENCE:

In Java: R.dimen.dimension_name
In XML: @[package:]dimen/dimension_name

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen
        name="dimension_name"
        >dimension</dimen>
</resources>

ELEMENTS:

EXAMPLE:

XML file saved at res/values/dimens.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen name="textview_height">25dp</dimen>
    <dimen name="textview_width">150dp</dimen>
    <dimen name="ball_radius">30dp</dimen>
    <dimen name="font_size">16sp</dimen>
</resources>

This application code retrieves a dimension:

Resources res = getResources();
float fontSize = res.getDimension(R.dimen.font_size);

This layout XML applies dimensions to attributes:

<TextView
    android:layout_height="@dimen/textview_height"
    android:layout_width="@dimen/textview_width"
    android:textSize="@dimen/font_size"/>

ID

A unique resource ID defined in XML. Using the name you provide in the <item> element, the Android developer tools create a unique integer in your project's R.java class, which you can use as an identifier for an application resources (for example, a View in your UI layout) or a unique integer for use in your application code (for example, as an ID for a dialog or a result code).

Note: An ID is a simple resource that is referenced using the value provided in the name attribute (not the name of the XML file). As such, you can combine ID resources with other simple resources in the one XML file, under one <resources> element. Also, remember that an ID resources does not reference an actual resource item; it is simply a unique ID that you can attach to other resources or use as a unique integer in your application.

FILE LOCATION:

res/values/filename.xml
The filename is arbitrary.

RESOURCE REFERENCE:

In Java: R.id.name
In XML: @[package:]id/name

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <item
        type="id"
        name="id_name" />
</resources>

ELEMENTS:

EXAMPLE:

XML file saved at res/values/ids.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <item type="id" name="button_ok" />
    <item type="id" name="dialog_exit" />
</resources>

Then, this layout snippet uses the "button_ok" ID for a Button widget:

<Button android:id="@id/button_ok"
    style="@style/button_style" />

Notice that the android:id value does not include the plus sign in the ID reference, because the ID already exists, as defined in the ids.xml example above. (When you specify an ID to an XML resource using the plus sign—in the format android:id="@+id/name"—it means that the "name" ID does not exist and should be created.)

As another example, the following code snippet uses the "dialog_exit" ID as a unique identifier for a dialog:

showDialog(R.id.dialog_exit);

In the same application, the "dialog_exit" ID is compared when creating a dialog:

protected Dialog onCreateDialog(int)(int id) {
    Dialog dialog;
    switch(id) {
    case R.id.dialog_exit:
        ...
        break;
    default:
        dialog = null;
    }
    return dialog;
}

Integer

An integer defined in XML.

Note: An integer is a simple resource that is referenced using the value provided in the name attribute (not the name of the XML file). As such, you can combine integer resources with other simple resources in the one XML file, under one <resources> element.

FILE LOCATION:

res/values/filename.xml
The filename is arbitrary. The <integer> element's name will be used as the resource ID.

RESOURCE REFERENCE:

In Java: R.integer.integer_name
In XML: @[package:]integer/integer_name

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <integer
        name="integer_name"
        >integer</integer>
</resources>

ELEMENTS:

EXAMPLE:

XML file saved at res/values/integers.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <integer name="max_speed">75</integer>
    <integer name="min_speed">5</integer>
</resources>

This application code retrieves an integer:

Resources res = getResources();
int maxSpeed = res.getInteger(R.integer.max_speed);

Integer Array

An array of integers defined in XML.

Note: An integer array is a simple resource that is referenced using the value provided in the name attribute (not the name of the XML file). As such, you can combine integer array resources with other simple resources in the one XML file, under one <resources> element.

FILE LOCATION:

res/values/filename.xml
The filename is arbitrary. The <integer-array> element's name will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

Resource pointer to an array of integers.

RESOURCE REFERENCE:

In Java: R.array.integer_array_name
In XML: @[package:]array.integer_array_name

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <integer-array
        name="integer_array_name">
        <item
            >integer</item>
    </integer-array>
</resources>

ELEMENTS:

EXAMPLE:

XML file saved at res/values/integers.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <integer-array name="bits">
        <item>4</item>
        <item>8</item>
        <item>16</item>
        <item>32</item>
    </integer-array>
</resources>

This application code retrieves the integer array:

Resources res = getResources();
int[] bits = res.getIntArray(R.array.bits);

Typed Array

A TypedArray defined in XML. You can use this to create an array of other resources, such as drawables. Note that the array is not required to be homogeneous, so you can create an array of mixed resource types, but you must be aware of what and where the data types are in the array so that you can properly obtain each item with the TypedArray's get...() methods.

Note: A typed array is a simple resource that is referenced using the value provided in the name attribute (not the name of the XML file). As such, you can combine typed array resources with other simple resources in the one XML file, under one <resources> element.

FILE LOCATION:

res/values/filename.xml
The filename is arbitrary. The <array> element's name will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

Resource pointer to a TypedArray.

RESOURCE REFERENCE:

In Java: R.array.array_name
In XML: @[package:]array.array_name

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <array
        name="integer_array_name">
        <item>resource</item>
    </array>
</resources>

ELEMENTS:

EXAMPLE:

XML file saved at res/values/arrays.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <array name="icons">
        <item>@drawable/home</item>
        <item>@drawable/settings</item>
        <item>@drawable/logout</item>
    </array>
    <array name="colors">
        <item>#FFFF0000</item>
        <item>#FF00FF00</item>
        <item>#FF0000FF</item>
    </array>
</resources>

This application code retrieves each array and then obtains the first entry in each array:

Resources res = getResources();
TypedArray icons = res.obtainTypedArray(R.array.icons);
Drawable drawable = icons.getDrawable(0);
TypedArray colors = res.obtainTypedArray(R.array.colors);
int color = colors.getColor(0,0);

*************************************************************

Accessing Resources in Code

When your Android application is compiled, a R class gets generated, which contains resource IDs for all the resources available in your res/ directory. You can use R class to access that resource using sub-directory and resource name or directly resource ID.

Example

To access res/drawable/myimage.png and set an ImageView you will use following code −

ImageView imageView = (ImageView) findViewById(R.id.myimageview);
imageView.setImageResource(R.drawable.myimage);

Here first line of the code make use of R.id.myimageview to get ImageView defined with id myimageview in a Layout file. Second line of code makes use of R.drawable.myimage to get an image with name myimage available in drawable sub-directory under /res.

Example

Consider next example where res/values/strings.xml has following definition −

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <string  name="hello">Hello, World!</string>
</resources>

Now you can set the text on a TextView object with ID msg using a resource ID as follows −

TextView msgTextView = (TextView) findViewById(R.id.msg);
msgTextView.setText(R.string.hello);

Example

Consider a layout res/layout/activity_main.xml with the following definition −

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent" 
   android:layout_height="fill_parent" 
   android:orientation="vertical" >
   
   <TextView android:id="@+id/text"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Hello, I am a TextView" />

   <Button android:id="@+id/button"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Hello, I am a Button" />
      
</LinearLayout>

This application code will load this layout for an Activity, in the onCreate() method as follows −

public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main_activity);
}

Accessing Resources in XML

Consider the following resource XML res/values/strings.xml file that includes a color resource and a string resource −

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <color name="opaque_red">#f00</color>
   <string name="hello">Hello!</string>
</resources>

Now you can use these resources in the following layout file to set the text color and text string as follows −

<?xml version="1.0" encoding="utf-8"?>
<EditText xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:textColor="@color/opaque_red"
   android:text="@string/hello" />

Inform It

Labels

Assignment Answer

Directory Structure of an Android Project(Anatomy)

src

gen

res

/res/values

/res/animator

/res/layout

/res/menu

/res/raw

/res/drawable

libs

assets

bin

AndroidManifest.xml

ic_launcher-web.png

proguard-project.txt

project.properties

Android assignment

Android Resources Organizing & Accessing

Bool

Color

Dimension

ID

Integer

Integer Array

Typed Array

Accessing Resources in Code

Example

Example

Example

Accessing Resources in XML

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