Android Resources
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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.
Organize Resources in eclipse
You should place each type of resource in a specific sub directory of your project's res/ directory. For example, here's the file hierarchy for a simple project:
MyProject/
src/
MyActivity.java
res/
drawable/
icon.png
layout/
activity_main.xml
info.xml
values/
strings.xml
The res/ directory contains all the resources in various sub directories. Here we have an image resource, two layout resources, and a string resource file. Following table gives a detail about the resource directories supported inside project res/ directory.
Organize resource in Android Studio
MyProject/
src/
main/
java/
MyActivity.java
res/
drawable/
icon.png
layout/
activity_main.xml
info.xml
values/
strings.xml
| Directory | Resource Type |
|---|---|
| anim/ | XML files that define property animations. They are saved in res/anim/ folder and accessed from the R.anim class. |
| color/ | XML files that define a state list of colors. They are saved in res/color/ and accessed from the R.color class. |
| drawable/ | Image files like .png, .jpg, .gif or XML files that are compiled into bitmaps, state lists, shapes, animation drawable. They are saved in res/drawable/ and accessed from the R.drawable class. |
| layout/ | XML files that define a user interface layout. They are saved in res/layout/ and accessed from the R.layout class. |
| menu/ | XML files that define application menus, such as an Options Menu, Context Menu, or Sub Menu. They are saved in res/menu/ and accessed from the R.menu class. |
| raw/ | Arbitrary files to save in their raw form. You need to callResources.openRawResource() with the resource ID, which is R.raw.filename to open such raw files. |
| values/ | XML files that contain simple values, such as strings, integers, and colors. For example, here are some filename conventions for resources you can create in this directory −
|
| xml/ | Arbitrary XML files that can be read at runtime by calling Resources.getXML(). You can save various configuration files here which will be used at run time. |
Alternative Resources
Your application should provide alternative resources to support specific device configurations. For example, you should include alternative drawable resources ( i.e.images ) for different screen resolution and alternative string resources for different languages. At runtime, Android detects the current device configuration and loads the appropriate resources for your application.
To specify configuration-specific alternatives for a set of resources, follow the following steps −
- Create a new directory in res/ named in the form <resources_name>-<config_qualifier>. Hereresources_name will be any of the resources mentioned in the above table, like layout, drawable etc. The qualifier will specify an individual configuration for which these resources are to be used. You can check official documentation for a complete list of qualifiers for different type of resources.
- Save the respective alternative resources in this new directory. The resource files must be named exactly the same as the default resource files as shown in the below example, but these files will have content specific to the alternative. For example though image file name will be same but for high resolution screen, its resolution will be high.
Below is an example which specifies images for a default screen and alternative images for high resolution screen.
MyProject/
src/
main/
java/
MyActivity.java
res/
drawable/
icon.png
background.png
drawable-hdpi/
icon.png
background.png
layout/
activity_main.xml
info.xml
values/
strings.xml
Below is another example which specifies layout for a default language and alternative layout for Arabic language.
MyProject/
src/
main/
java/
MyActivity.java
res/
drawable/
icon.png
background.png
drawable-hdpi/
icon.png
background.png
layout/
activity_main.xml
info.xml
layout-ar/
main.xml
values/
strings.xml
Accessing Resources
During your application development you will need to access defined resources either in your code, or in your layout XML files. Following section explains how to access your resources in both the scenarios −
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 myimageavailable 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" />
Now if you will go through previous chapter once again where I have explained Hello World! example, and I'm sure you will have better understanding on all the concepts explained in this chapter. So I highly recommend to check previous chapter for working example and check how I have used various resources at very basic level.
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