What is the role of attachBaseContext?

Question

I am confused about why do we use attachBaseContext in android. It would be a great help if someone could explain to me the meaning for the same.

Answer 1

The attachBaseContext function of the ContextWrapper class is making sure the context is attached only once. ContextThemeWrapper applies theme from application or Activity which is defined as android:theme in the AndroidManifest.xml file. Since both Application and Service do not need theme, they inherit it directly from ContextWrapper. During the activity creation, application and service are initiated, a new ContextImpl object is created each time and it implements functions in Context.

public class ContextWrapper extends Context {
    Context mBase;

    public ContextWrapper(Context base) {
        mBase = base;
    }

    /**
     * Set the base context for this ContextWrapper.  All calls will then be
     * delegated to the base context.  Throws
     * IllegalStateException if a base context has already been set.
     * 
     * @param base The new base context for this wrapper.
     */
    protected void attachBaseContext(Context base) {
        if (mBase != null) {
            throw new IllegalStateException("Base context already set");
        }
        mBase = base;
    }

}

For more details please look this.