Android: What is android.R.id.content used for?

Question

Anybody could explain the meaning of "android.R.id.content" ?

How is it being used ?

http://developer.android.com does not have any explanation.

public static final int content
Since: API Level 1

Constant Value: 16908290 (0x01020002)

Answer 1

As Philipp Reichart commented:

android.R.id.content gives you the root element of a view, without having to know its actual name/type/ID. Check out http://stackoverflow.com/questions/4486034/android-how-to-get-root-view-from-current-activity

Answer 2

The android.R.id.content ID value indicates the ViewGroup of the entire content area of an Activity.

It can be used with Fragment:

public class MyActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                .add(android.R.id.content, MyFragment.newInstance())
                .commit();
        }
    }

    ...

}

The code above will insert the View created by Fragment into the ViewGroup identified by android.R.id.content.

Answer 3

Google designers develop Android UX with specific or recommended design guidelines. The layout android.R.id.content defines a linearlayout with a few attributes Android believes are a good standard.

Thus loading a Fragment Manager's root view with android.R.id.content ensures these guidelines are implemented.

NOTE: This layout has set the attribute: android:addStatesFromChildren="true" to allow child fragments to overwrite attributes in this rootview.

As of version 19, android.R.id.content is defined in a file: auto_complete_list.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/content"
    android:orientation="vertical"
    android:layout_width="match_parent" 
    android:layout_height="wrap_content"
    android:background="@android:drawable/edit_text"
    android:divider="@android:drawable/divider_horizontal_textfield"
    android:addStatesFromChildren="true">