问题是，onPanChanged()方法被调用两次，导致点在每次用户移动或平移地图时绘制之前都会闪烁。我该怎么做才能使onPanChanged()方法只被调用一次。在代码中，我甚至尝试关闭侦听器并在退出AsyncTask时将其重新打开。
我希望您能分享一些想法和意见。
// MapActivity
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.SharedPreferences;
import android.graphics.drawable.Drawable;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapController;
import com.google.android.maps.MapView;
import com.google.android.maps.Overlay;
import com.google.android.maps.OverlayItem;
public class MapActivityNearby extends MapActivity implements EnhancedMapView.OnPanChangeListener {
private EnhancedMapView mv;
private static final String TAG = "MAPACTIVITY";
private static final String PREF_NAME = "cookie";
private double lat;
private double lng;
private ArrayList<MapItem> allCats;
private GeoPoint p;
private float latMin;
private float latMax;
private float longMin;
private float longMax;
private MapController mapControl;
private List<Overlay> mapOverlays;
private MyItemizedOverlay itemizedOverlay;
boolean waitTime = true;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.map_nearby);
LinearLayout ll = (LinearLayout) findViewById(R.id.maplayout);
mv = new EnhancedMapView(this, "api_key");
mv.setClickable(true);
mv.setBuiltInZoomControls(true);
mv.setOnZoomChangeListener(new EnhancedMapView.OnZoomChangeListener() {
@Override
public void onZoomChange(MapView view, int newZoom, int oldZoom) {
Log.d("test", "zoom changed from " + oldZoom + " to " + newZoom);
}
});
ViewGroup.LayoutParams lp = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
mv.setLayoutParams(lp);
ll.addView(mv);
SharedPreferences cookies = getSharedPreferences(PREF_NAME,
Context.MODE_PRIVATE);
lat = Double.parseDouble(cookies.getString("lat", "0"));
lng = Double.parseDouble(cookies.getString("lng", "0"));
GeoPoint p = new GeoPoint((int) (lat * 1E6), (int) (lng * 1E6));
mapControl = mv.getController();
mapControl.setZoom(11);
mapControl.setCenter(p);
}
public void onResume()
{
super.onResume();
if (isNetworkAvailable(MapActivityNearby.this))
{
PlotPoints plot = new PlotPoints();
plot.execute(mv);
}
else
{
AlertDialog.Builder builder = new AlertDialog.Builder(MapActivityNearby.this);
builder.setMessage("No network connection. Please try again when your within coverage area.")
.setTitle("Network Connection")
.setCancelable(false)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
//close dialog
}
});
AlertDialog alert = builder.create();
alert.show();
}
}
@Override
protected boolean isRouteDisplayed() {
// TODO Auto-generated method stub
return false;
}
public void plotPoints(ArrayList<MapItem> i) {
mapOverlays = mv.getOverlays();
// first overlay
Drawable drawable;
drawable = getResources().getDrawable(R.drawable.marker);
itemizedOverlay = new MyItemizedOverlay(drawable, mv);
mapOverlays.add(itemizedOverlay);
for (MapItem x : i) {
GeoPoint point = new GeoPoint((int) (x.getLat() * 1E6),
(int) (x.getLng() * 1E6));
OverlayItem overlayItem = new OverlayItem(point,
x.getTitle(), x.getSubtitle());
itemizedOverlay.addOverlay(overlayItem);
}
GeoPoint point = new GeoPoint((int) (((latMin + latMax) * 1E6) / 2), (int) (((longMin + longMax) * 1E6) /2));
MapController mc = mv.getController();
mc.setCenter(point);
}
private class PlotPoints extends AsyncTask<EnhancedMapView, Void, Boolean> {
String result = "";
InputStream is;
@Override
protected void onPreExecute() {
turnOff();
}
@Override
protected Boolean doInBackground(EnhancedMapView...params) {
turnOff();
int maxCount = 100;
EnhancedMapView mapView = params[0];
for (int i = 0; i < maxCount; i++)
{
p = mapView.getMapCenter();
float latCenter = (float) (p.getLatitudeE6()) / 1000000;
float longCenter = (float) (p.getLongitudeE6()) / 1000000;
float latSpan = (float) (mapView.getLatitudeSpan()) / 1000000;
float longSpan = (float) (mapView.getLongitudeSpan()) / 1000000;
latMax = latCenter + (latSpan/2);
latMin = latCenter - (latSpan/2);
longMax = longCenter + (longSpan/2);
longMin = longCenter - (longSpan/2);
if (latMin == latMax)
{
try
{
Thread.sleep(80);
}
catch(InterruptedException e)
{
}
}
else
{
p = mapView.getMapCenter();
latCenter = (float) (p.getLatitudeE6()) / 1000000;
longCenter = (float) (p.getLongitudeE6()) / 1000000;
latSpan = (float) (mapView.getLatitudeSpan()) / 1000000;
longSpan = (float) (mapView.getLongitudeSpan()) / 1000000;
latMax = latCenter + (latSpan/2);
latMin = latCenter - (latSpan/2);
longMax = longCenter + (longSpan/2);
longMin = longCenter - (longSpan/2);
break;
}
}
log(latMin);
log(latMax);
try {
final String catURL = "url";
log(catURL.toString());
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(catURL);
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("PHPSESSID", getCookie()));
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
result = convertStreamToString();
log(result);
allCats = new ArrayList<MapItem>();
JSONObject object = new JSONObject(result);
JSONArray temp = object.getJSONArray("l");
log("Starting download");
log(temp.length());
long start = System.currentTimeMillis();
for (int k = 0; k < temp.length(); k++) {
JSONObject j = temp.getJSONObject(k);
MapItem c = new MapItem();
c.setObject_id(j.getInt("object_id"));
c.setTitle(j.getString("title"));
c.setColor(j.getString("color"));
c.setLat(j.getDouble("lat"));
c.setLng(j.getDouble("lng"));
c.setSubtitle(j.getString("subtitle"));
allCats.add(c);
log(allCats.toString());
}
long end = System.currentTimeMillis();
log("Download Took: " + (end - start) / 1000 + " seconds.");
// log(allCats.toString());
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return true;
}
@Override
protected void onPostExecute(Boolean results) {
// pBar.setVisibility(View.GONE);
plotPoints(allCats);
turnOn();
}
private String convertStreamToString() {
try {
BufferedReader reader = new BufferedReader(
new InputStreamReader(is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
result.trim();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
return result;
}
}
public String getCookie() {
String cookie = "";
SharedPreferences cookies = getSharedPreferences(PREF_NAME,
Context.MODE_PRIVATE);
if (cookies.contains("cookie")) {
cookie = cookies.getString("cookie", "null");
}
return cookie;
}
private void log(Object obj) {
Log.d(TAG, TAG + " :: " + obj.toString());
}
public static boolean isNetworkAvailable(Context context) {
ConnectivityManager connectivity = (ConnectivityManager) context
.getSystemService(Context.CONNECTIVITY_SERVICE);
if (connectivity != null) {
NetworkInfo[] info = connectivity.getAllNetworkInfo();
if (info != null) {
for (int i = 0; i < info.length; i++) {
if (info[i].getState() == NetworkInfo.State.CONNECTED) {
return true;
}
}
}
}
return false;
}
@Override
public void onPanChange(MapView view, GeoPoint newCenter, GeoPoint oldCenter) {
Log.d("test", "center changed from " + oldCenter.getLatitudeE6() + "," + oldCenter.getLongitudeE6() + " to " + newCenter.getLatitudeE6() + "," + newCenter.getLongitudeE6());
if(!mv.getOverlays().isEmpty())
{
mv.getOverlays().clear();
mv.postInvalidate();
}
if (isNetworkAvailable(MapActivityNearby.this))
{
PlotPoints log = new PlotPoints();
log.execute(mv);
}
else
{
AlertDialog.Builder builder = new AlertDialog.Builder(MapActivityNearby.this);
builder.setMessage("No network connection. Please try again when your within coverage area.")
.setTitle("Network Connection")
.setCancelable(false)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
//close dialog
}
});
AlertDialog alert = builder.create();
alert.show();
}
}
public void turnOn ()
{
mv.setOnPanChangeListener(this);
}
public void turnOff ()
{
mv.setOnPanChangeListener(null);
}
}
// EnhancedMapView
import java.util.Timer;
import java.util.TimerTask;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapView;
public class EnhancedMapView extends MapView {
public interface OnZoomChangeListener {
public void onZoomChange(MapView view, int newZoom, int oldZoom);
}
public interface OnPanChangeListener {
public void onPanChange(MapView view, GeoPoint newCenter, GeoPoint oldCenter);
}
private EnhancedMapView _this;
// Set this variable to your preferred timeout
private long events_timeout = 500L;
private boolean is_touched = false;
private GeoPoint last_center_pos;
private int last_zoom;
private Timer zoom_event_delay_timer = new Timer();
private Timer pan_event_delay_timer = new Timer();
private EnhancedMapView.OnZoomChangeListener zoom_change_listener;
private EnhancedMapView.OnPanChangeListener pan_change_listener;
public EnhancedMapView(Context context, String apiKey) {
super(context, apiKey);
_this = this;
last_center_pos = this.getMapCenter();
last_zoom = this.getZoomLevel();
}
public EnhancedMapView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public EnhancedMapView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public void setOnZoomChangeListener(EnhancedMapView.OnZoomChangeListener l) {
zoom_change_listener = l;
}
public void setOnPanChangeListener(EnhancedMapView.OnPanChangeListener l) {
pan_change_listener = l;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (ev.getAction() == 1) {
is_touched = false;
} else {
is_touched = true;
}
return super.onTouchEvent(ev);
}
@Override
public void computeScroll() {
super.computeScroll();
if (getZoomLevel() != last_zoom) {
// if computeScroll called before timer counts down we should drop it and start it over again
zoom_event_delay_timer.cancel();
zoom_event_delay_timer = new Timer();
zoom_event_delay_timer.schedule(new TimerTask() {
@Override
public void run() {
zoom_change_listener.onZoomChange(_this, getZoomLevel(), last_zoom);
last_zoom = getZoomLevel();
}
}, events_timeout);
}
// Send event only when map's center has changed and user stopped touching the screen
if (!last_center_pos.equals(getMapCenter()) && !is_touched) {
pan_event_delay_timer.cancel();
pan_event_delay_timer = new Timer();
try
{
pan_event_delay_timer.schedule(new TimerTask() {
@Override
public void run() {
try
{
pan_change_listener.onPanChange(_this, getMapCenter(), last_center_pos);
last_center_pos = getMapCenter();
}
catch (IllegalArgumentException e)
{
Log.v("IllegalArgumentException", e.toString());
}
catch (IllegalStateException e)
{
Log.v("IllegalStateException", e.toString());
}
catch (NullPointerException e)
{
Log.v("NullPointerException", e.toString());
}
}
}, events_timeout);
}
catch (IllegalArgumentException e)
{
Log.v("IllegalArgumentException", e.toString());
}
catch (IllegalStateException e)
{
Log.v("IllegalStateException", e.toString());
}
catch (NullPointerException e)
{
Log.v("NullPointerException", e.toString());
}
}
}
}