ArcGIS for Android 之Query的初步使用

本文的代码是来自Sample里面的QueryTask的例子。自己看Api很久后，觉得还是拿这个例子作为自己的入门学习。比较省时方便。
首先需要自己了解mapview的状态监听器的Api：

OnStatusChangedListener接口用于监听MapView或Layer状态变化的监听器，用法如下：

1.//添加状态监听器  2.mapView.setOnStatusChangedListener(new OnStatusChangedListener() {    3.            public void onStatusChanged(Object source, STATUS status) {  4.                if(status == STATUS.INITIALIZED){                     5.                }else if(status == STATUS.LAYER_LOADED){                      6.                }else if((status == STATUS.INITIALIZATION_FAILED)){               7.                }else if((status == STATUS.LAYER_LOADING_FAILED)){                8.                }                 9.            }  10.        });  

从上面的代码我们可以清晰看到，对于MapView的状态变化主要有四种：

1)      STATUS.INITIALIZED初始化成功

2)      STATUS.LAYER_LOADED图层加载成功

3)      STATUS.INITIALIZATION_FAILED初始化失败

4)      STATUS.LAYER_LOADING_FAILED图层加载失败

下面是做个注释和调试成功过的java代码：

/* Copyright 2010 ESRI * * All rights reserved under the copyright laws of the United States * and applicable international laws, treaties, and conventions. * * You may freely redistribute and use this sample code, with or * without modification, provided you include the original copyright * notice and use restrictions. * * See the sample code usage restrictions document for further information. * */package com.esri.arcgis.android.samples.querytask;import android.app.Activity;import android.app.ProgressDialog;import android.graphics.Color;import android.os.AsyncTask;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.Toast;import com.esri.android.map.GraphicsLayer;import com.esri.android.map.Layer;import com.esri.android.map.MapView;import com.esri.android.map.ags.ArcGISTiledMapServiceLayer;import com.esri.android.map.event.OnStatusChangedListener;import com.esri.arcgis.android.samples.attributequery.R;import com.esri.core.geometry.Envelope;import com.esri.core.geometry.SpatialReference;import com.esri.core.map.FeatureSet;import com.esri.core.map.Graphic;import com.esri.core.renderer.SimpleRenderer;import com.esri.core.symbol.SimpleFillSymbol;import com.esri.core.tasks.ags.query.Query;import com.esri.core.tasks.ags.query.QueryTask;public class AttributeQuery extends Activity {/** Called when the activity is first created. */MapView mv;GraphicsLayer gl;Graphic graphic;Graphic fillGraphic;Button querybt;String targetServerURL = "http://services.arcgisonline.com/ArcGIS/rest/services/Demographics/USA_Average_Household_Size/MapServer";boolean blQuery = true;ProgressDialog progress;final static int HAS_RESULTS = 1;final static int NO_RESULT = 2;final static int CLEAR_RESULT = 3;public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);mv = (MapView) findViewById(R.id.map);mv.setOnStatusChangedListener(new OnStatusChangedListener() {private static final long serialVersionUID = 1L;public void onStatusChanged(Object source, STATUS status) {if (source == mv && status == STATUS.INITIALIZED) {gl = new GraphicsLayer();SimpleRenderer sr = new SimpleRenderer(new SimpleFillSymbol(Color.RED));// 设置渲染器gl.setRenderer(sr);mv.addLayer(gl);boolean doQuery = false;for (Layer lv : mv.getLayers()) {if (lv instanceof ArcGISTiledMapServiceLayer) {ArcGISTiledMapServiceLayer tLayer = (ArcGISTiledMapServiceLayer) lv;if (tLayer.getUrl().equals(targetServerURL)) {doQuery = true;break;}}}if (!doQuery) {Toast toast = Toast.makeText(AttributeQuery.this,"URL for query does not exist any more",Toast.LENGTH_LONG);toast.show();} else {querybt.setEnabled(true);}}}});querybt = (Button) findViewById(R.id.queryButton);querybt.setOnClickListener(new View.OnClickListener() {public void onClick(View v) {if (blQuery) {String targetLayer = targetServerURL.concat("/3");String[] queryParams = { targetLayer, "AVGHHSZ_CY>3.5" };AsyncQueryTask ayncQuery = new AsyncQueryTask();ayncQuery.execute(queryParams);} else {gl.removeAll();blQuery = true;querybt.setText("Average Household > 3.5");}}});}/** *  * 异步执行查询任务. *  */private class AsyncQueryTask extends AsyncTask<String, Void, FeatureSet> {protected void onPreExecute() {// 在未查询出结果时显示一个进度条progress = ProgressDialog.show(AttributeQuery.this, "","Please wait....query task is executing");}protected FeatureSet doInBackground(String... queryParams) {if (queryParams == null || queryParams.length <= 1)return null;// 查询条件和URL参数String url = queryParams[0];// 查询所需的参数类Query query = new Query();String whereClause = queryParams[1];SpatialReference sr = SpatialReference.create(102100);// 建立一个空间参考// WKID_WGS84_WEB_MERCATOR_AUXILIARY_SPHERE（102100）query.setGeometry(new Envelope(-20147112.9593773, 557305.257274575,-6569564.7196889, 11753184.6153385));// 设置查询空间范围query.setOutSpatialReference(sr);// 设置查询输出的坐标系query.setReturnGeometry(true);// 是否返回空间信息query.setWhere(whereClause);// where条件QueryTask qTask = new QueryTask(url);// 查询任务类FeatureSet fs = null;Log.i(null, "doInBackground is running !");try {fs = qTask.execute(query);// 执行查询，返回查询结果} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();return fs;}return fs;}protected void onPostExecute(FeatureSet result) {Log.i(null, "onPostExecute is running !");String message = "No result comes back";if (result != null) {Graphic[] grs = result.getGraphics();if (grs.length > 0) {// gl = new GraphicsLayer();// SimpleRenderer sr = new SimpleRenderer(// new SimpleFillSymbol(Color.RED));// 设置渲染器// gl.setRenderer(sr);gl.addGraphics(grs); // 将查询结果添加到图层上// mv.addLayer(gl);message = (grs.length == 1 ? "1 result has " : Integer.toString(grs.length) + " results have ")+ "come back";}}progress.dismiss();// 停止进度条Toast toast = Toast.makeText(AttributeQuery.this, message,Toast.LENGTH_LONG);toast.show();querybt.setText("Clear graphics");blQuery = false;Log.i(null, "onPostExecute is finish !");}}@Overrideprotected void onPause() {super.onPause();mv.pause();}@Overrideprotected void onResume() {super.onResume();mv.unpause();}}

从中，可以看出重点在于对query和query Task的定义上，url必须要知道你是需要查询的内容是什么方面的。其中可以借鉴的就是那个进度条的使用，该什么时候显示出来，什么时候关闭它。可以用于以后大量的搜索的功能上做一个过渡。

效果图：