重写TiledServiceLayer实现本地缓存

        有时候移动端网络不是很稳定，而且在没有Wifi情况下访问非常费流量，网速也较慢，因此实现本地缓存功能已经显得刻不容缓了。虽然现在Arcgis官方对Android还不支持这个功能，但我们完全可以自己去实现。其实思路很简单，就是在每次访问服务端的之前去判断本地是否有这个图片，如果有就读取本地的，否则去服务端获取并保存到本地。可以更形象一点：

if(本地是否有这个切片)｛         读取本地图片；   ｝else{         去服务端获取；         保存到本地；      }

对就是这么简单，下面我们看代码。

一些的参数

 private Envelope fullExtent = new Envelope(38271382.590048, 3958604.25302, 38524317.872452, 4118706.90518);//全服范围    private Envelope initExtent = new Envelope(38271382.590048, 3958604.25302, 38524317.872452, 4118706.90518);//初始范围    private TileInfo tileInfo; //TiledServiceLayer.TileInfo            private SpatialReference spatialReference;//空间参考            private String layerurl; //Url    private String cachepath;//本地存储路径

初始化Tileinfo

private void initTileInfo(){                spatialReference = SpatialReference.create(2363); //空间参考/*原点坐标*/        Point localPoint = new Point(3.28768E7,1.00021E7);        /*地图分辨率*/double[] arrayOfDoubleres = {529.16772500211675, 264.58386250105838, 132.29193125052919, 66.145965625264594, 33.072982812632297, 16.933367200067735,8.4666836000338677,4.2333418000169338, 2.1166709000084669, 1.0583354500042335, 0.52916772500211673, 0.26458386250105836};       /*地图比例尺*/       double[] arrayOfDoublescale = {2000000.0, 1000000.0, 500000.0, 250000.0, 125000.0, 64000.0, 32000.0, 16000.0,                                         8000.0, 4000.0, 2000.0, 1000.0};       int levels = arrayOfDoublescale.length;       int dpi=96;       int tileHeight = 256;//图片高度       int tileWidth = 256;//图片宽度       tileInfo = new TileInfo(localPoint, arrayOfDoublescale, arrayOfDoubleres,levels, dpi, tileWidth, tileHeight);}

重载initLayer()方法

@Overrideprotected void initLayer() {// TODO Auto-generated method stubif(getID()==0){this.nativeHandle = create();}setFullExtent(fullExtent);//设置全服地图范围setTileInfo(tileInfo);//设置tileInfosetInitialExtent(initExtent);//设置初始化地图范围setDefaultSpatialReference(spatialReference);//设置空间参考super.initLayer();}

重载geTile()方法

@Overrideprotected byte[] getTile(int level, int col, int row) throws Exception {// TODO Auto-generated method stubbyte[] bytes = getOfflineCacheFile(level,col,row);//从本地获取图片   if (bytes == null) {//如果本地没有则去服务端获取HashMap localHashMap = new HashMap();bytes = a.a(strlayer, localHashMap);AddOfflineCacheFile(level, col, row, bytes);//保存到本地    }}return bytes;}

下面是完整的代码

package com.test.common.utils;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.util.HashMap;import android.util.Log;import com.esri.android.map.TiledServiceLayer;import com.esri.core.geometry.Envelope;import com.esri.core.geometry.Point;import com.esri.core.geometry.SpatialReference;import com.esri.core.internal.b.a.a;/** *  * @ClassName:   OfflineCacheTiledServiceLayer * @Description: 实现本地缓存 * @author：              Zrd * @version：            v1.0   * @modify:      TODO(版本修改信息) */public class OfflineCacheTiledServiceLayer  extends TiledServiceLayer {    private SpatialReference spatialReference; //空间参考    private Envelope fullExtent = new Envelope(38271382.590048, 3958604.25302, 38524317.872452, 4118706.90518);//全服范围    private Envelope initExtent = new Envelope(38271382.590048, 3958604.25302, 38524317.872452, 4118706.90518);//初始范围    private TileInfo tileInfo; //TiledServiceLayer.TileInfo        private String layerurl; //Url    private String cachepath;//本地存储路径    public OfflineCacheTiledServiceLayer(String layerurl,String cachepath) {super(layerurl);// TODO Auto-generated constructor stubthis.layerurl = layerurl;this.cachepath = cachepath;initTileInfo();OfflineCacheTiledServiceLayer.this.initLayer();}private void initTileInfo(){spatialReference = SpatialReference.create(2363); //空间参考/*原点坐标*/        Point localPoint = new Point(3.28768E7,1.00021E7);        /*地图分辨率*/    double[] arrayOfDoubleres = {529.16772500211675, 264.58386250105838, 132.29193125052919, 66.145965625264594, 33.072982812632297, 16.933367200067735,8.4666836000338677,4.2333418000169338, 2.1166709000084669, 1.0583354500042335, 0.52916772500211673, 0.26458386250105836};    /*地图比例尺*/    double[] arrayOfDoublescale = {2000000.0, 1000000.0, 500000.0, 250000.0, 125000.0, 64000.0, 32000.0, 16000.0, 8000.0, 4000.0, 2000.0, 1000.0};int k = arrayOfDoublescale.length;int dpi=96;int tileHeight = 256;//图片高度    int tileWidth = 256;//图片宽度tileInfo = new TileInfo(localPoint, arrayOfDoublescale, arrayOfDoubleres, k, dpi, tileWidth, tileHeight);}@Overrideprotected void initLayer() {// TODO Auto-generated method stubif(getID()==0){this.nativeHandle = create();}setFullExtent(fullExtent);//设置全服地图范围setTileInfo(tileInfo);//设置tileInfosetInitialExtent(initExtent);//设置初始化地图范围setDefaultSpatialReference(spatialReference);//设置空间参考super.initLayer();}@Overridepublic TileInfo getTileInfo() {// TODO Auto-generated method stubreturn this.tileInfo;}@Overridepublic Envelope getFullExtent() {// TODO Auto-generated method stubreturn this.fullExtent;}@Overridepublic SpatialReference getSpatialReference() {// TODO Auto-generated method stubreturn this.spatialReference;}@Overrideprotected byte[] getTile(int level, int col, int row) throws Exception {// TODO Auto-generated method stubSystem.out.println("level=" + level + " col=" + col + " row=" + row);String strlayer = layerurl+"/tile/"+level+"/"+row+"/"+col;System.out.println(strlayer);Log.i("strlayer", strlayer);byte[] bytes = getOfflineCacheFile(level,col,row);    if (bytes == null) {HashMap localHashMap = new HashMap();bytes = a.a(strlayer, localHashMap);Log.e("test", bytes.toString());AddOfflineCacheFile(level, col, row, bytes);    }}return bytes;}//将图片保存到本地 目录结构可以随便定义 只要你找得到对应的图片private byte[] AddOfflineCacheFile(int level, int col, int row,byte[] bytes){File file = new File(cachepath);if(!file.exists()){file.mkdirs();}File levelfile = new File(cachepath+"/"+level);if(!levelfile.exists()){levelfile.mkdirs();}File colfile = new File(cachepath+"/"+level+"/"+col);if(!colfile.exists()){colfile.mkdirs();}File rowfile = new File(cachepath+"/"+level+"/"+col+"/"+row+".dat");if(!rowfile.exists()){try {FileOutputStream out = new FileOutputStream(rowfile);out.write(bytes);} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}return bytes;}//从本地获取图片private byte[] getOfflineCacheFile(int level, int col, int row){byte[] bytes = null;File rowfile = new File(cachepath+"/"+level+"/"+col+"/"+row+".dat");if(rowfile.exists()){try {bytes = CopySdcardbytes(rowfile);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}else{bytes = null;}return bytes;}        //读取本地图片流public byte[] CopySdcardbytes(File file) throws IOException      {          FileInputStream in = new FileInputStream(file);                    ByteArrayOutputStream out = new ByteArrayOutputStream(1024);                    byte[] temp=new byte[1024];                    int size=0;                    while((size=in.read(temp))!=-1)          {              out.write(temp,0,size);          }          in.close();          byte[] bytes=out.toByteArray();          return bytes;      }  }