On zoom event for google maps on android

Question

We\'re building an application which is using the google maps api for android.

I have my MapController and MapView, and I enable the built-in zoom controls using:

Answer 1

For pre-V2.0, I made a class which extends MapView that alerts a listener with events when the map region starts changing (onRegionBeginChange) and stops changing (onRegionEndChange).

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapView;

public class ExMapView extends MapView {
    private static final String TAG = ExMapView.class.getSimpleName();
    private static final int DURATION_DEFAULT = 700;

    private OnRegionChangedListener onRegionChangedListener;
    private GeoPoint previousMapCenter;
    private int previousZoomLevel;
    private int changeDuration; // This is the duration between when the user stops moving the map around and when the onRegionEndChange event fires.
    private boolean isTouched = false;
    private boolean regionChanging = false;

    private Runnable onRegionEndChangeTask = new Runnable() {
        public void run() {
            regionChanging = false;
            previousMapCenter = getMapCenter();
            previousZoomLevel = getZoomLevel();
            if (onRegionChangedListener != null) {
                onRegionChangedListener.onRegionEndChange(ExMapView.this, previousMapCenter, previousZoomLevel);
            }
        }
    };

    public ExMapView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public ExMapView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    public ExMapView(Context context, String apiKey) {
        super(context, apiKey);
        init();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        isTouched = event.getAction() != MotionEvent.ACTION_UP;
        return super.onTouchEvent(event);
    }

    @Override
    public void computeScroll() {
        super.computeScroll();

        // If the map region is still changing (user is still scrolling or zooming), reset timer for onRegionEndChange.
        if ((!isTouched && !getMapCenter().equals(previousMapCenter)) || (previousZoomLevel != getZoomLevel())) {

            // If the region has just begun changing, fire off onRegionBeginChange event.
            if (!regionChanging) {
                regionChanging = true;
                if (onRegionChangedListener != null) {
                    onRegionChangedListener.onRegionBeginChange(this, previousMapCenter, previousZoomLevel);
                }
            }

            // Reset timer for onRegionEndChange.
            removeCallbacks(onRegionEndChangeTask);
            postDelayed(onRegionEndChangeTask, changeDuration);
        }
    }

    private void init() {
        changeDuration = DURATION_DEFAULT;
        previousMapCenter = getMapCenter();
        previousZoomLevel = getZoomLevel();
    }

    public void setOnRegionChangedListener(OnRegionChangedListener listener) {
        onRegionChangedListener = listener;
    }

    public void setChangeDuration(int duration) {
        changeDuration = duration;
    }

    public interface OnRegionChangedListener {
        public abstract void onRegionBeginChange(ExMapView exMapView, GeoPoint geoPoint, int zoomLevel);
        public abstract void onRegionEndChange(ExMapView exMapView, GeoPoint geoPoint, int zoomLevel);
    }
}

Answer 2

I use this library which has an onZoom function listener. http://code.google.com/p/mapview-overlay-manager/. Works well.

Answer 3

I used a mixture of the above. I found that using the timmer to start a thread every half a second cause the map to be really jenky. Probably because I was using a couple of If statments everytime. So I started the thread on a post delay of 500ms from the onUserInteraction. This gives enough time for the zoomLevel to update before the thread starts to run thus getting the correct zoomlevel without running a thread every 500ms.

public void onUserInteraction() {
    handler.postDelayed(zoomChecker, zoomCheckingDelay);
}

Answer 4

You can implement your own basic "polling" of the zoom value to detect when the zoom has been changed using the android Handler.

Using the following code for your runnable event. This is where your processing should be done.

private Handler handler = new Handler();

public static final int zoomCheckingDelay = 500; // in ms

private Runnable zoomChecker = new Runnable()
{
    public void run()
    {
        checkMapIcons();

        handler.removeCallbacks(zoomChecker); // remove the old callback
        handler.postDelayed(zoomChecker, zoomCheckingDelay); // register a new one
    }
};

Start a callback event using

protected void onResume()
{
    super.onResume();
    handler.postDelayed(zoomChecker, zoomCheckingDelay);
}

and stop it when you're leaving the activity using

protected void onPause()
{
    super.onPause();
    handler.removeCallbacks(zoomChecker); // stop the map from updating
}

Article this is based on can be found here if you want a longer write up.

Answer 5

U can have Zoom CControl like this.

Here i am attaching code how u can implement zoomcontrol.

1>> XML file should be like this.

<?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">

    <com.google.android.maps.MapView 
        android:id="@+id/mapView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:enabled="true"
        android:clickable="true"
        android:apiKey="0l4sCTTyRmXTNo7k8DREHvEaLar2UmHGwnhZVHQ"
        />

    <LinearLayout android:id="@+id/zoom" 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:layout_alignParentBottom="true" 
        android:layout_centerHorizontal="true" 
        /> 

</RelativeLayout>

2>> On you main activity inside oncreate method do following things. here you are inflating your view with mapView

mapView = (MapView) findViewById(R.id.mapView);
        LinearLayout zoomLayout = (LinearLayout)findViewById(R.id.zoom);  
        View zoomView = mapView.getZoomControls(); 

        zoomLayout.addView(zoomView, 
            new LinearLayout.LayoutParams(
                LayoutParams.WRAP_CONTENT, 
                LayoutParams.WRAP_CONTENT)); 
        mapView.displayZoomControls(true);

........................................................... This is how you can use inbuilt zoom control of API..

You can have your own custom code to implement Zoom in And Zoom out like this...

public boolean onKeyDown(int keyCode, KeyEvent event) 
{
    MapController mc = mapView.getController(); 
    switch (keyCode) 
    {
        case KeyEvent.KEYCODE_3:
            mc.zoomIn();
            break;
        case KeyEvent.KEYCODE_1:
            mc.zoomOut();
            break;
    }
    return super.onKeyDown(keyCode, event);
}    

..This is how i have implemented...

Thanks..Rakesh