Android Resources management

Android Resources access

There's a lot to build for a great Android app. I n addition to application encoding, you need to focus on a variety of resources, such as the various static content you use, such as bitmaps, colors, layout definitions, user interface strings, animations, and so on. These resources are typically placed in the project's res/under-separate subdirector.

This tutorial will learn how to organize application resources, specify alternative resources, and access them in your application.

Organize resources in eclipse

You need to place each resource under a specific subdirector in the project res/directory. For example, this is the file level of 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 subdirectdirectles. H ere is a picture resource, two layout resources, and a string resource file. The following table details the resources supported in the project res/directory.

Alternative resources

Your application needs to provide alternative resource support for a specific device configuration. F or example, you need to provide alternative picture resources for different screen resolutions and alternative string resources for different languages. At runtime, Android detects the current device configuration and loads the appropriate resources for the application.

To identify a series of alternative resources for a specific configuration, follow these steps:

• Create a new directory under res/, resource_name in the form config_qualifier. T he resources_name is any of the resources mentioned in the table above, such as layouts, pictures, and so on. Q ualifier determines which resources are used for personality configuration. You can view the official documentation for a complete list of different types of resources.
• Save an alternative resource for the response in this directory. T hese resource files must match the default resource file names shown in the following examples, however, they replace what they determine. For example, although the file name of the picture is the same, the resolution of the picture is also high on a high-resolution screen.

Below is an example that specifies the default screen for the picture and a high-resolution alternative picture.

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

Here's another example, specifying the layout of the default language and an alternative layout for the 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

Access to resources

In application development, you need access to well-defined resources, whether through code or XML files. The following sections describe how to access resources in both scenarios.

Access resources in code

When the Android application is compiled, an R class is generated that contains the ID of all the resources in the res/directory. You can use the R class to access resources through sub-classes and resource names, or directly with resource IDs.

Instance

Visit the res/drawable/myimage .png and set it up on ImageView, and you'll use the following code:

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

The first line of code here uses R.id.myimageview to get ImageView defined as myimageview in the layout file. The second line uses R.drawable.myimage to get a picture called myimage under the drawable subdirecter of res/.

Instance

Consider the next example, where the res/values/strings .xml as follows:

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

Now you can use the resource ID to set the text on a TextView object with an ID of msg, as follows:

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

Instance

Consider the layout res/layout/activity_main.xml

<?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 the activity, as follows in the onCreate() method:

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

Access in XML

Consider the following XML resource file res/values/strings .xml, which contains a color resource and a string resource -

<?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" />

You can now use these resources in the following layout files to set the text color and text content:

<?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 go back to the previous chapter, "Hello World! " Examples, I can be sure that you have a better understanding of all the concepts in this section. So, I strongly recommend going back to the previous example and looking at the basic usage of different resources.