Android Tutorial - Android Layout Resources

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In Android, the view for a screen is often loaded from an XML file. These XML files are called layout resources.

Example

The following shows an example of a Layout File

<?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/text1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

    <Button
        android:id="@+id/b1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />
</LinearLayout>

Note

Each file in the /res/layout/ subdirectory generates a unique constant based on the name of the file with extension excluded.

With layouts, what matters is the number of files. With string resources, what matters is the number of individual string resources inside the files.

For example, if you have two files under /res/layout/ called file1.xml and file2.xml, then in R.java you have the following entries.

public static final class layout {
    //.... any other files
    public static final int file1=0x7f030000;
    public static final int file2=0x7f030001;
    //....
}

Reference

The views defined in these layout files, such as a TextView, are accessible in Java code through their resource IDs generated in R.java:

TextView tv = (TextView)this.findViewById(R.id.text1);
tv.setText("Try this text instead");

The constant R.id.text1 corresponds to the ID defined for the TextView. The ID for the TextView in the layout file is as follows:

<TextView android:id="@+id/text1"
..
</TextView>

The value for the id attribute indicates that a constant called text1 is used to uniquely identify this view.

The plus sign (+) in @+id/text1 means the ID text1 will be created if it doesn't exist already.

Use string resource in layout resource

Once you've defined the strings as resources, you can set them directly on a view.

The following example shows an example where an HTML string is set as the text content of a TextView.

The following code is for string.xml.

<resources>
    <string name="simple_string">simple string</string>
    <string name="tagged_string">
         Hello <b><i>Slanted Android</i></b>, You are bold.
    </string>
</resources>

The following code is for layout.xml.

<TextView android:layout_width="fill_parent"
          android:layout_height="wrap_content"
          android:gravity="center_horizontal"
          android:text="@string/tagged_string"/>

The TextView automatically realizes that this string is an HTML string and honors its formatting accordingly.

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