Android与位置相关的应用开发(2)-MapController与Overlay

在前一节中演示了MapView的简单应用，MapView从服务的提供方获取相关数据并且将地图显示出来，此外通过MapView还可以显示如卫星图，交通等信息；在本文中将介绍另外两个重要类MapController和Overlay，这两个类将丰富地图的功能和展示。
1）MapController：
如果要在地图中设置缩放等级、实现缩放功能和动态移动等功能需要使用另一个重要的类MapController，MapController的简单使用如下：

 @Override
	public void onCreate(Bundle icicle) {
		super.onCreate(icicle);
		setContentView(R.layout.mapview);
		mapView = (MapView) findViewById(R.id.mapview);
		mapView.setBuiltInZoomControls(true);
		Drawable marker = getResources().getDrawable(R.drawable.mapmarker);
		marker.setBounds(0, 0, marker.getIntrinsicWidth(),
				marker.getIntrinsicHeight());
		InterestingLocations interestPlaces = new InterestingLocations(marker);
		mapView.getOverlays().add(interestPlaces);
		GeoPoint pt = interestPlaces.getCenter();
		mapView.getController().setCenter(pt);
		mapView.getController().setZoom(15);
	}

通过setCenter(GeoPoint)设置当前地图显示的中心位置，setZoom(zoomLevel)设置当前地图的缩放等级，通过zoomIn()和zoomOut()实现地图的缩放；
2）Overlay：
在使用地图的时候我们希望将我们感兴趣的位置在地图上标示出来，这个时候我们将使用覆盖图，将我们感兴趣的位置用覆盖图在地图上标示出来，android提供了一些简单的Overlay的实现方式，在这里演示最简单ItemizedOverlay，代码如下：

 @SuppressWarnings("rawtypes")
	class InterestingLocations extends ItemizedOverlay {
		private Drawable marker;

		private List<OverlayItem> locations = new ArrayList<OverlayItem>();

		public InterestingLocations(Drawable defaultMarker) {
			super(defaultMarker);
			marker = defaultMarker;
			GeoPoint disneyMagicKingdom = new GeoPoint((int) (28.418971 * 1E6),
					(int) (-81.581436 * 1E6));
			GeoPoint disneySevenLagoon = new GeoPoint((int) (28.410067 * 1E6),
					(int) (-81.583699 * 1E6));
			locations.add(new OverlayItem(disneyMagicKingdom, "Magic Kingdom",
					"Magic Kingdom"));
			locations.add(new OverlayItem(disneySevenLagoon, "Seven Sea Lagoon",
					"Seven Sea Lagoon"));
			populate();
		}

		@Override
		protected OverlayItem createItem(int index) {
			return locations.get(index);
		}

		@Override
		public int size() {
			return locations.size();
		}

		@Override
		public void draw(Canvas canvas, MapView mapView, boolean shadow) {
			super.draw(canvas, mapView, shadow);
			boundCenterBottom(marker);
		}
	}
}

该类要求提供一个覆盖图id，然后将感兴趣的位置GeoPoint添加至位置列表中；
再通过MapView.getOverlays().Add(Overlay)将覆盖图列表添加至MapView上用于显示；
本节完整代码如下：
layout文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <com.google.android.maps.MapView
        android:id="@+id/mapview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:apiKey="your api key"
        android:clickable="true" />

</LinearLayout>

Activity代码：

package com.local;

import java.util.ArrayList;
import java.util.List;

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.Drawable;
import android.os.Bundle;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.ItemizedOverlay;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapView;
import com.google.android.maps.OverlayItem;

public class MappingOverlayActivity extends MapActivity {

	private MapView mapView;

	@Override
	public void onCreate(Bundle icicle) {
		super.onCreate(icicle);
		setContentView(R.layout.mapview);
		mapView = (MapView) findViewById(R.id.mapview);
		mapView.setBuiltInZoomControls(true);
		Drawable marker = getResources().getDrawable(R.drawable.mapmarker);
		marker.setBounds(0, 0, marker.getIntrinsicWidth(),
				marker.getIntrinsicHeight());
		InterestingLocations interestPlaces = new InterestingLocations(marker);
		mapView.getOverlays().add(interestPlaces);
		GeoPoint pt = interestPlaces.getCenter();
		mapView.getController().setCenter(pt);
		mapView.getController().setZoom(14);
	}

	@Override
	protected boolean isRouteDisplayed() {
		return false;
	}

	@SuppressWarnings("rawtypes")
	class InterestingLocations extends ItemizedOverlay {
		private Drawable marker;

		private List<OverlayItem> locations = new ArrayList<OverlayItem>();

		public InterestingLocations(Drawable defaultMarker) {
			super(defaultMarker);
			marker = defaultMarker;
			GeoPoint hubin = new GeoPoint((int) (30.254618 * 1E6),
					(int) (120.163650 * 1E6));
			GeoPoint mateng = new GeoPoint((int) (30.278637 * 1E6),
					(int) (120.150260 * 1E6));
			locations.add(new OverlayItem(hubin, "外婆家湖滨店", "外婆家湖滨店"));
			locations.add(new OverlayItem(mateng, "外婆家马塍店", "外婆家马塍店"));
			populate();
		}

		@Override
		protected OverlayItem createItem(int index) {
			return locations.get(index);
		}

		@Override
		public int size() {
			return locations.size();
		}

		@Override
		public void draw(Canvas canvas, MapView mapView, boolean shadow) {
			Paint paint = new Paint();
			paint.setTextSize(12);
			paint.setColor(Color.BLUE);
			for (OverlayItem item : locations) {
				Point point = mapView.getProjection().toPixels(item.getPoint(),
						null);
				canvas.drawText(item.getTitle(), point.x, point.y-20, paint);
			}
			super.draw(canvas, mapView, shadow);
			boundCenterBottom(marker);
		}
	}
}

运行结果如下：