GIS的学习（三十九）针对osmdroid的扩展之MyLocationOverlay

          在许多用地图应用中，在地图第一次加载的时候，可能将用户当前的位置定位的地图的中心，有时候可能有一个定位的功能，那么当点击点位的时候，需要地图的以当前用户所在位置为中心那么就需要重写MyLocationOverlay类实现相关的功能。

针对MyLocationOverlay的重写如下：

package com.etrip.osmdroid;
import org.osmdroid.util.GeoPoint;
import org.osmdroid.views.MapController;
import org.osmdroid.views.MapView;
import org.osmdroid.views.overlay.MyLocationOverlay;
import com.etrip.osmdroid.R;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Point;
import android.location.Location;
/**
 * 重写的目的是在于
 * 1.让当前的位置位于地图的中心位置
 * 
 * 
 * 原文：
 *   http://stackoverflow.com/questions/4175432/mylocationoverlay-change-the-marker
 *   
 *   如果想改变当前位置的图标和标记颜色，可以采用以下两种方式实现：
 *   Step #1: Create a subclass of MyLocationOverlay.
 *   Step #2: Override drawMyLocation() 
 *   
 *   
 *   
 * 
 */
public class CurrentLocationOverlay extends MyLocationOverlay {    
	private final static int PADDING_ACTIVE_ZOOM     = 50;    
	private MapController    mc;   
	private Bitmap           marker;   
	private Point            currentPoint            = new Point();    
	private boolean          centerOnCurrentLocation = true;    
	private int              height;   
	private int              width;    
	/**    
	 * By default this CurrentLocationOverlay will center on the current location, 
	 * if the currentLocation is near the    
	 * edge, or off the screen. To dynamically enable/disable this, 
	 * use {@link #setCenterOnCurrentLocation(boolean)}.    
	 * @param context    
	 * @param mapView    
	 */   
	public CurrentLocationOverlay(Context context, MapView mapView) {     
		super(context, mapView);     
		this.mc = mapView.getController();    
		this.marker = BitmapFactory.decodeResource(context.getResources(), R.drawable.marker_default);   
	}    
	protected void drawMyLocation(Canvas canvas, MapView mapView, Location lastFix, GeoPoint myLocation, long when) {  
		if (this.height == 0) {       
			this.height = mapView.getHeight();       
			this.width = mapView.getWidth();    
		}    
		mapView.getProjection().toPixels(myLocation, currentPoint); 
		
		canvas.drawBitmap(marker, currentPoint.x, currentPoint.y - 40, null);   
	}    
	@Override   
	public synchronized void onLocationChanged(Location location) {     
		super.onLocationChanged(location);    
		// only move to new position if enabled and we are in an border-area
		if (mc != null && centerOnCurrentLocation && inZoomActiveArea(currentPoint)) {
			mc.animateTo(getMyLocation());  
			setCenterOnCurrentLocation(true);
		}   
	}    
	private boolean inZoomActiveArea(Point currentPoint) {     
		if ((currentPoint.x > PADDING_ACTIVE_ZOOM && currentPoint.x < width - PADDING_ACTIVE_ZOOM) && (currentPoint.y > PADDING_ACTIVE_ZOOM && currentPoint.y < height - PADDING_ACTIVE_ZOOM)) {       
			return false;     
		}     
		return true;   
	}    
	public void setCenterOnCurrentLocation(boolean centerOnCurrentLocation) {     
		this.centerOnCurrentLocation = centerOnCurrentLocation;   
	} 
}

测试代码如下：

package com.etrip.osmdroid;

import org.osmdroid.tileprovider.tilesource.TileSourceFactory;
import org.osmdroid.util.GeoPoint;
import org.osmdroid.views.MapController;
import org.osmdroid.views.MapView;

import android.app.Activity;
import android.os.Bundle;

/**
 * 
 * 
 * 
 * @author longgangbai
 */
public class MainActivity extends Activity {

		private MapController mapController;   
	    private MapView mapView;   
	    /** Called when the activity is first created. */  
	    @Override  
	    public void onCreate(final Bundle savedInstanceState) {   
	        super.onCreate(savedInstanceState);   
	        setContentView(R.layout.activity_main);   
	        mapView = (MapView) findViewById(R.id.map);   
	        mapView.setTileSource(TileSourceFactory.MAPNIK);    
	        mapView.setBuiltInZoomControls(true);   
	        mapController = mapView.getController();   
	        mapController.setZoom(8);  
	        CurrentLocationOverlay locationOverlay=new CurrentLocationOverlay(this,mapView);
	        locationOverlay.enableCompass();
	        locationOverlay.enableFollowLocation();
	        locationOverlay.enableMyLocation();
	        //GeoPoint geopoint=new GeoPoint(39.92605, 116.42616);    
	       // mapController.setCenter(locationOverlay.getMyLocation()); 
	        mapView.getOverlays().add(locationOverlay);
	     }   
}