问题
I am trying to get markers placed on the map and fly to their destination. within a forloop i have an if statement, i wish it to do this:
for(i loop){
If (array(i) == null{ spawn plane code}
else {move plane code}
here is the code:
package com.fly.plane;
import java.sql.Time;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.fly.plane.R;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.MapView;
import com.google.android.gms.maps.Projection;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import android.R.array;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.graphics.Point;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.SystemClock;
import android.support.v4.app.FragmentActivity;
import android.text.format.DateFormat;
import android.util.Log;
import android.view.View;
import android.view.animation.Interpolator;
import android.view.animation.LinearInterpolator;
import android.widget.TextView;
public class MyMapActivity extends ListActivity {
private ProgressDialog pDialog;
// URL to get data JSON
private static String url = "http://edmundgentle.com/snippets/flights/api.php";
// JSON Node speeds
private static final String TAG_data = "data";
private static final String TAG_BEARING = "bearing";
private static final String TAG_SPEED = "speed";
private static final String TAG_ARR = "arr";
private static final String TAG_ARR_TIME = "time";
private static final String TAG_ARR_LAT = "lat";
private static final String TAG_ARR_LON = "lon";
private static final String TAG_DEP = "dep";
private static final String TAG_DEP_TIME = "time";
private static final String TAG_DEP_LAT = "lat";
private static final String TAG_DEP_LON = "lon";
// data JSONArray
JSONArray data = null;
// Hashmap for ListView
ArrayList<HashMap<String, Double>> contactList;
// Hashmap for ListView
ArrayList<Double> ct;
List<Marker> markers = new ArrayList<Marker>();
//final Handler handler;
private GoogleMap mMap;
public static final LatLng dest(Double alt,Double aln, int i){
//final double latitude = Double.parseDouble(alt);
//final double longitude = Double.parseDouble(aln);
return new LatLng(alt, aln);
}
public double latt = -15.48169437461;
public double lng = -15.48169437461;
public ArrayList<Integer> dLat;
public String[] markerList;
public String dlat;
public String dlon;
public String alat;
public String alon;
private int count;
public boolean wait = true;
//private Button startB;
public TextView text;
Timer timing;
double time = 600;
double timm = 1;
long timer = 18000000;
long newTime;
TextView tv, test;
Thread t;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_map);
contactList = new ArrayList<HashMap<String, Double>>();
ct = new ArrayList<Double>();
//ListView lv = getListView();
//create markers
new Getdata().execute();
// timer showing time of day in fast time
t = new Thread() {
@Override
public void run() {
try {
while (!isInterrupted()) {
Thread.sleep(600);
runOnUiThread(new Runnable() {
@Override
public void run() {
timer = timer +60000;
if (timer >= 64000000) timer = 18000000;
newTime = timer;
// update TextView here!
//String time = "HH:mm:ss";
//tv.setText(DateFormat.format(time , timer));
tv.setText(Double.toString(time));
test.setText(Double.toString(timm));
//tv.setText(Double.toString(contactList.get(20).get("time")));
//Timer();
}
});
}
} catch (InterruptedException e) {
}
}
};
tv = new TextView(this);
test = new TextView(this);
tv=(TextView)findViewById(R.id.timer);
test=(TextView)findViewById(R.id.test);
// run the mUpdateUITimerTask's run() method in 10 seconds from now
}
// animate each plane
public void animateMarker(final Marker marker , final LatLng toPosition,
final boolean hideMarker, final double spd) {
float speed = (float) spd;// Float.parseFloat(spd);
final Handler handler = new Handler();
final long start = SystemClock.uptimeMillis();
Projection proj = mMap.getProjection();
Point startPoint = proj.toScreenLocation(marker.getPosition());
final LatLng startLatLng = proj.fromScreenLocation(startPoint);
final float duration = 10 * speed;
final Interpolator interpolator = new LinearInterpolator();
handler.post(new Runnable() {
@Override
public void run() {
long elapsed = SystemClock.uptimeMillis() - start;
float t = interpolator.getInterpolation((float) ((float) elapsed
/ duration));
double lng = t * toPosition.longitude + (1 - t)
* startLatLng.longitude;
double lat = t * toPosition.latitude + (1 - t)
* startLatLng.latitude;
marker.setPosition(new LatLng(lat, lng));
if (t < 1.0) {
// Post again 16ms later.
handler.postDelayed(this, 16);
} else {
handler.postDelayed(this, 16);
if (hideMarker) {
marker.setVisible(false);
} else {
marker.setVisible(true);
}
}
}
});
}
public void Timer(){
//TimerTask tasknew = new TimerTask();
timing = new Timer();
timing.schedule(new CreateMarker(), 1000, 1000);
}
public String calcCurPos(double curlat, double curlon, double deslat, double deslon, double avgSpd, double bearing){
double distance = avgSpd * 0.0167;
// check if degrees or radians
//deslat = distance * Math.cosh(bearing);
//double retLat = curlat + deslat;
//double dPhi = Math.log(Math.tan(retLat/2+Math.PI/4)/Math.tan(curlat/2+Math.PI/4));
//double q = deslat/dPhi deslat/dPhi : Math.cos(curlat);
bearing = bearing * Math.PI / 180;
int radius = 6371;
double nextLat = Math.asin(Math.sin(curlat)* Math.cos(distance/radius)
+ Math.cos(curlat)*Math.sin(distance/radius)*Math.cos(bearing));
double nextLon = curlon + Math.atan2(Math.sin(bearing)* Math.sin(distance/ radius)
* Math.cos(curlat), Math.cos(distance/radius)-Math.sin(curlat) * Math.sin(nextLat));
nextLat = (nextLat * 180) / Math.PI;
nextLon = (nextLon * 180) / Math.PI;
/**
* Warning might want to convert them to string prior to return.
*/
return nextLat + ";" + nextLon;
}
public class CreateMarker extends TimerTask{
@Override
public void run() {
// TODO Auto-generated method stub
// print test
//tv.setText(Double.toString(time));
//tv.setText(Double.toString(time));
if (time >= 2400){
time=0;
}
time += 1;
//mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
for (int i =0; i < 100;i++){
// get data from array list
final double depLat = contactList.get(i).get("dlat");
final double depLon = contactList.get(i).get("dlon");
final double arLat = contactList.get(i).get("alat");
final double arLon = contactList.get(i).get("alon");
final double spd = contactList.get(i).get("speed");
final double dTime = contactList.get(i).get("time");
double curLat = contactList.get(i).get("clat");
double curLon = contactList.get(i).get("clon");
final double bearing = contactList.get(i).get("bearing");
final int j = i;
//int dTime = Integer.parseInt(dtime);
double oldLat = curLat;
if (time >= dTime)
{
if (curLat < arLat || curLat > 0){
String latlng = calcCurPos(curLat, curLon, arLat, arLon ,spd, bearing );
String[] values = latlng.split(";");
curLat = Double.parseDouble(values[0]);
curLon = Double.parseDouble(values[1]);
final double crLat = curLat;
final double crLon = curLon;
final LatLng position = new LatLng(crLat,crLon);
/*Marker mo = mMap.addMarker(new MarkerOptions()
.position(new LatLng(depLat, depLon))
.icon(BitmapDescriptorFactory.fromResource(R.drawable.planemarker)));*/
//DrawMarker();
//animateMarker(markers.get(i), position , true, spd);
try{
if (markers.get(i) == null){
//timm += 1;
timm += 1;
runOnUiThread(new Runnable() {
@Override
public void run() {
final Marker marker = mMap.addMarker(new MarkerOptions()
.position(new LatLng(depLat, depLon))
.title("Hello world")
.icon(BitmapDescriptorFactory.fromResource(R.drawable.planemarker)));
markers.add(marker);
//marker.setVisible(false);
//animateMarker(markers.get(j), new LatLng(arLat,arLon) , true, spd);
//Marker marker = markers.get(i);
//marker.setPosition(position);
}
});
}
else //(markers.get(i) != null){
{
Marker marker = markers.get(i);
marker.setPosition(position);
marker.setVisible(false);
//animateMarker(markers.get(i), position , true, spd);
}
}
catch(NullPointerException npe)
{
//do something else
}
}
}
}
//return null;
}
}
/**
* Async task class to get json by making HTTP call
* */
private class Getdata extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(MyMapActivity.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
HTTPHandler sh = new HTTPHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url, HTTPHandler.GET);
Log.d("Response: ", "> " + jsonStr);
boolean limit = false;
if (jsonStr != null || limit == false) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// Getting JSON Array node
data = jsonObj.getJSONArray(TAG_data);
// looping through All data
for (int i = 0; i < data.length(); i++) {
JSONObject c = data.getJSONObject(i);
String bearing = c.getString(TAG_BEARING);
String spd = c.getString(TAG_SPEED);
// departure node is JSON Object
JSONObject dep = c.getJSONObject(TAG_DEP);
String dtime = dep.getString(TAG_DEP_TIME);
//String dlat = dep.getString(TAG_DEP_LAT);
//String dlon = dep.getString(TAG_DEP_LON);
dlat = dep.getString(TAG_DEP_LAT);
dlon = dep.getString(TAG_DEP_LON);
// replace : and last 2 0's from departure time
dtime = dtime.replaceAll(":","");
//dtime.replaceAll(";","");
dtime = dtime.substring(0,dtime.length()-2);
// arrival node is JSON Object
JSONObject arr = c.getJSONObject(TAG_ARR);
String alt = arr.getString(TAG_ARR_LAT);
String aln = arr.getString(TAG_ARR_LON);
// convert data positions to doubles for Google Maps + stuff
double brng = Double.parseDouble(bearing);
brng = brng * Math.PI / 180;
double speed = Double.parseDouble(spd);
//double brng = Double.parseDouble(bearing);
double dLatitude = Double.parseDouble(dlat);
double dLongitude = Double.parseDouble(dlon);
double aLatitude = Double.parseDouble(alt);
double aLongitude = Double.parseDouble(aln);
double cLatitude = Double.parseDouble(dlat);
double cLongitude = Double.parseDouble(dlon);
double dtme = Double.parseDouble(dtime);
// tmp hashmap for single contact
HashMap<String, Double> contact = new HashMap<String, Double>();
contact.put("bearing", brng);
contact.put("speed", speed);
contact.put("time", dtme);
contact.put("alat", aLatitude);
contact.put("alon", aLongitude);
contact.put("dlat", dLatitude);
contact.put("dlon", dLongitude);
contact.put("clat", cLatitude);
contact.put("clon", cLongitude);
// adding contact to contact list
contactList.add(contact);
if (i== data.length()){
wait = false;
}
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
// spawns planes when json loaded
@Override
protected void onPostExecute(Void result) {
Timer();
t.start();
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
// use plane api for latlon
mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
//for (int i = 0; i < contactList.size() ; i++)
}}
}
and here is the error message:
02-26 21:53:42.031: E/AndroidRuntime(14970): FATAL EXCEPTION: Timer-0
02-26 21:53:42.031: E/AndroidRuntime(14970): java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
02-26 21:53:42.031: E/AndroidRuntime(14970): at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
02-26 21:53:42.031: E/AndroidRuntime(14970): at java.util.ArrayList.get(ArrayList.java:308)
02-26 21:53:42.031: E/AndroidRuntime(14970): at com.fly.plane.MyMapActivity$CreateMarker.run(MyMapActivity.java:395)
02-26 21:53:42.031: E/AndroidRuntime(14970): at java.util.Timer$TimerImpl.run(Timer.java:284)
i understand that the markers.get(i) is causing the problem, but i dont know how to check if the markers array is null without it throwing this error.
Any help would be appreciated.
回答1:
You can use Map<Integer, Marker> (Integer are keys and Marker are values). Then you can leverage Map.get() which don't throws Exception if key is Integer and not null (your i will not be null in your code).
Declare markers as Map:
Map<Integer, Marker> markers = new HashMap<Integer, Marker>();
Inside CreateMarker.run() after final LatLng position = new LatLng(crLat,crLon); change as follows:
//implicit boxing to use int in Map
Integer ii = Integer.valueOf(i);
//try to get marker by index from map (index is the key)
Marker markerByIndex = markers.get(ii);
//Map.get() returns null if object by specified key is not in map
if (markerByIndex == null){
//marker doesn't exists - create it, add to Google Map and to Map by key
timm += 1;
runOnUiThread(new Runnable() {
@Override
public void run() {
final Marker marker = mMap.addMarker(new MarkerOptions()
.position(new LatLng(depLat, depLon))
.title("Hello world")
.icon(BitmapDescriptorFactory.fromResource(R.drawable.planemarker)));
//put marker to map using i as a key
markers.put(ii, marker);
}
});
} else {
//marker exists, mutate it
markerByIndex.setPosition(position);
markerByIndex.setVisible(false);
//...replace the marker in map
markers.put(ii, markerByIndex);
//animate the marker
animateMarker(markerByIndex, position , true, spd);
}
回答2:
You wrote:
i understand that the markers.get(i) is causing the problem, but i dont know how to check if the markers array is null without it throwing this error.
==> you can check it this way:
if (markers != null && markers.size() > 0) {
//there are actually markers. Calling markers.get(i) should work!
//...as long as i is smaller than markers.size()
} else {
//sorry, no markers! Don't call markers.get(i) here...
}
来源：https://stackoverflow.com/questions/22054311/google-maps-android-indexoutofboundsexception