问题描述
- 关于arcgis for android 中的QueryTask这个例子的一些问题
-
在下面的源码中我主要有几点不明白 请各位大神能够帮助解答第一、这个个例子中是什么时候开始对地图进行初始化的啊？ 在xml文件中的url="http://www.arcgis.com/home/webmap/viewer.html?webmap=58e58acce685442aa4c73f91fbb3a387"这句话是对该地图进行初始化吗？ 为什么不是一个mapserver啊？
代码片段，双击复制
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/map" android:layout_width="fill_parent"
android:layout_height="fill_parent"
url="http://www.arcgis.com/home/webmap/viewer.html?webmap=58e58acce685442aa4c73f91fbb3a387"
>第二 、对于代码中的以下部分不明白
if (source == mv && status == STATUS.INITIALIZED) {
gl = new GraphicsLayer();
SimpleRenderer sr = new SimpleRenderer(
new SimpleFillSymbol(Color.RED));
gl.setRenderer(sr);//设置渲染图形层
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; } } }那个for循环中的的代码是用来干什么的啊？
以下是程序源码
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.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)); gl.setRenderer(sr);//设置渲染图形层 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"); } } }); } /** * * Query Task executes asynchronously. * */ private class AsyncQueryTask extends AsyncTask<String, Void, FeatureSet> { protected void onPreExecute() { progress = ProgressDialog.show(AttributeQuery.this, "", "Please wait....query task is executing"); } /** * First member in parameter array is the query URL; second member is * the where clause. */ protected FeatureSet doInBackground(String... queryParams) { if (queryParams == null || queryParams.length <= 1) return null; String url = queryParams[0]; Query query = new Query(); String whereClause = queryParams[1]; SpatialReference sr = SpatialReference.create(102100); query.setGeometry(new Envelope(-20147112.9593773, 557305.257274575, -6569564.7196889, 11753184.6153385)); query.setOutSpatialReference(sr); query.setReturnGeometry(true); query.setWhere(whereClause); QueryTask qTask = new QueryTask(url); FeatureSet fs = null; try { fs = qTask.execute(query); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); return fs; } return fs; } protected void onPostExecute(FeatureSet result) { String message = "No result comes back"; if (result != null) { Graphic[] grs = result.getGraphics(); if (grs.length > 0) { gl.addGraphics(grs); message = (grs.length == 1 ? "1 result has " : Integer .toString(grs.length) + " results have ") + "come back"; } } progress.dismiss(); Toast toast = Toast.makeText(AttributeQuery.this, message, Toast.LENGTH_LONG); toast.show(); querybt.setText("Clear graphics"); blQuery = false; } } @Override protected void onPause() { super.onPause(); mv.pause();}
@Override protected void onResume() {
super.onResume();
mv.unpause();
}}