Android :: google maps on double tap zoom in

How hard is it to make a simple zoom in call on double tap in MapView in Android?

Not very.

How hard is it to get the information on how to do it?

Very.

Here's what you probably didn't know:
You need to extend the MapView and use this extended class in the Android XML layout file.
In the extended class you instantiate the gesture detector and set on double tap listener.
In the Map Activity you implement OnGestureListener and OnDoubleTapListener.

Example:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center_horizontal" >
    
 <net.kafol.vlaki.ExtMapView
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/mapview"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:clickable="true"
     android:enabled="true"
     android:apiKey=""
 />

</RelativeLayout>

package net.kafol.vlaki;

import android.content.Context;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.GestureDetector.OnDoubleTapListener;
import android.view.MotionEvent;
import android.view.GestureDetector.OnGestureListener;
import com.google.android.maps.MapView;

public class ExtMapView extends MapView {
 private Context context;
 private GestureDetector gestureDetector;

 public ExtMapView(Context c, AttributeSet attrs) {
  super(c, attrs);
  context = c;

  gestureDetector = new GestureDetector((OnGestureListener) context);
  gestureDetector.setOnDoubleTapListener((OnDoubleTapListener) context);
 }

 public boolean onTouchEvent(MotionEvent ev) {
  if (this.gestureDetector.onTouchEvent(ev))
   return true;
  else
   return super.onTouchEvent(ev);
 }
}

public class Map extends MapActivity implements OnGestureListener, OnDoubleTapListener {
...
 @Override
 public boolean onDoubleTap(MotionEvent e) {
     int x = (int)e.getX(), y = (int)e.getY();;
     Projection p = mapView.getProjection();
     mapView.getController().animateTo(p.fromPixels(x, y)); // zoom in to a point you tapped 
     mapView.getController().zoomIn();
  return true;
 }