I followed some tutorials to create an application that shows the current position of the user on the map with a marking. But for some reasons I can't get to work the marking part? The other parts work well, but whenever I add the marking code the application crashes.
Here is the code:
public class LocationActivity extends MapActivity {
private MapView mapView;
private LocationManager lm;
private LocationListener ll;
private MapController mc;
GeoPoint p = null;
Drawable defaultMarker = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mapView = (MapView) findViewById(R.id.mapView);
// show zoom in/out buttons
mapView.setBuiltInZoomControls(true);
// Standard view of the map(map/sat)
mapView.setSatellite(false);
// get controller of the map for zooming in/out
mc = mapView.getController();
// Zoom Level
mc.setZoom(18);
MyLocationOverlay myLocationOverlay = new MyLocationOverlay();
List<Overlay> list = mapView.getOverlays();
list.add(myLocationOverlay);
lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
ll = new MyLocationListener();
lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, ll);
// Get the current location in start-up
GeoPoint initGeoPoint = new GeoPoint((int) (lm.getLastKnownLocation(
LocationManager.GPS_PROVIDER).getLatitude() * 1000000),
(int) (lm.getLastKnownLocation(LocationManager.GPS_PROVIDER)
.getLongitude() * 1000000));
mc.animateTo(initGeoPoint);
}
protected class MyLocationOverlay extends com.google.android.maps.Overlay {
@Override
public boolean draw(Canvas canvas, MapView mapView, boolean shadow,
long when) {
Paint paint = new Paint();
super.draw(canvas, mapView, shadow);
// Converts lat/lng-Point to OUR coordinates on the screen.
Point myScreenCoords = new Point();
mapView.getProjection().toPixels(p, myScreenCoords);
paint.setStrokeWidth(1);
paint.setARGB(255, 255, 255, 255);
paint.setStyle(Paint.Style.STROKE);
Bitmap bmp = BitmapFactory.decodeResource(getResources(),
R.drawable.push);
canvas.drawBitmap(bmp, myScreenCoords.x, myScreenCoords.y, paint);
canvas.drawText("I am here...", myScreenCoords.x, myScreenCoords.y,
paint);
return true;
}
}
private class MyLocationListener implements LocationListener {
public void onLocationChanged(Location argLocation) {
GeoPoint myGeoPoint = new GeoPoint(
(int) (argLocation.getLatitude() * 1000000),
(int) (argLocation.getLongitude() * 1000000));
/*
* it will show a message on location change
* Toast.makeText(getBaseContext(), "New location latitude ["
* +argLocation.getLatitude() + "] longitude [" +
* argLocation.getLongitude()+"]", Toast.LENGTH_SHORT).show();
*/
mc.animateTo(myGeoPoint);
}
public void onProviderDisabled(String provider) {}
public void onProviderEnabled(String provider) {}
public void onStatusChanged(String provider, int status, Bundle extras) {}
}
protected boolean isRouteDisplayed() {
return false;
}
}
here is the logcat:
01-19 05:31:43.011: DEBUG/AndroidRuntime(759): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<<
01-19 05:31:43.011: DEBUG/AndroidRuntime(759): CheckJNI is ON
01-19 05:31:43.411: DEBUG/AndroidRuntime(759): --- registering native functions ---
01-19 05:31:43.431: INFO/jdwp(759): received file descriptor 19 from ADB
01-19 05:31:43.431: INFO/jdwp(759): Ignoring second debugger -- accepting and dropping
01-19 05:31:44.531: INFO/ActivityManager(583): Starting activity: Intent { flg=0x10000000 cmp=pro.googlemapp/.LocationActivity }
01-19 05:31:44.641: DEBUG/AndroidRuntime(759): Shutting down VM
01-19 05:31:44.641: DEBUG/dalvikvm(759): DestroyJavaVM waiting for non-daemon threads to exit
01-19 05:31:44.641: DEBUG/dalvikvm(759): DestroyJavaVM shutting VM down
01-19 05:31:44.641: DEBUG/dalvikvm(759): HeapWorker thread shutting down
01-19 05:31:44.651: DEBUG/dalvikvm(759): HeapWorker thread has shut down
01-19 05:31:44.651: DEBUG/jdwp(759): JDWP shutting down net...
01-19 05:31:44.651: DEBUG/jdwp(759): +++ peer disconnected
01-19 05:31:44.651: INFO/dalvikvm(759): Debugger has detached; object registry had 1 entries
01-19 05:31:44.661: DEBUG/dalvikvm(759): VM cleaning up
01-19 05:31:44.681: INFO/ActivityManager(583): Start proc pro.googlemapp for activity pro.googlemapp/.LocationActivity: pid=770 uid=10025 gids={3003}
01-19 05:31:44.761: DEBUG/dalvikvm(759): LinearAlloc 0x0 used 676436 of 4194304 (16%)
01-19 05:31:44.801: INFO/jdwp(770): received file descriptor 20 from ADB
01-19 05:31:44.822: INFO/dalvikvm(770): ignoring registerObject request in thread=3
01-19 05:31:44.851: INFO/jdwp(770): Ignoring second debugger -- accepting and dropping
01-19 05:31:44.851: ERROR/jdwp(770): Failed writing handshake bytes: Broken pipe (-1 of 14)
01-19 05:31:44.851: INFO/dalvikvm(770): Debugger has detached; object registry had 0 entries
01-19 05:31:45.320: ERROR/ActivityThread(770): Failed to find provider info for com.google.settings
01-19 05:31:45.320: ERROR/ActivityThread(770): Failed to find provider info for com.google.settings
01-19 05:31:45.340: ERROR/ActivityThread(770): Failed to find provider info for com.google.settings
01-19 05:31:45.781: DEBUG/LocationManager(770): Constructor: service = android.location.ILocationManager$Stub$Proxy@4379d9f0
01-19 05:31:45.791: WARN/GpsLocationProvider(583): Duplicate add listener for uid 10025
01-19 05:31:45.791: DEBUG/GpsLocationProvider(583): setMinTime 0
01-19 05:31:45.791: DEBUG/GpsLocationProvider(583): startNavigating
01-19 05:31:45.831: INFO/jdwp(770): received file descriptor 27 from ADB
01-19 05:31:46.001: INFO/MapActivity(770): Handling network change notification:CONNECTED
01-19 05:31:46.001: ERROR/MapActivity(770): Couldn't get connection factory client
01-19 05:31:46.451: DEBUG/dalvikvm(770): GC freed 4539 objects / 298952 bytes in 118ms
01-19 05:31:46.470: DEBUG/AndroidRuntime(770): Shutting down VM
01-19 05:31:46.470: WARN/dalvikvm(770): threadid=3: thread exiting with uncaught exception (group=0x4001aa28)
01-19 05:31:46.481: ERROR/AndroidRuntime(770): Uncaught handler: thread main exiting due to uncaught exception
01-19 05:31:46.541: ERROR/AndroidRuntime(770): java.lang.NullPointerException
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at com.google.android.maps.PixelConverter.toPixels(PixelConverter.java:58)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at com.google.android.maps.PixelConverter.toPixels(PixelConverter.java:48)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at pro.googlemapp.LocationActivity$MyLocationOverlay.draw(LocationActivity.java:101)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at com.google.android.maps.OverlayBundle.draw(OverlayBundle.java:42)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at com.google.android.maps.MapView.onDraw(MapView.java:476)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.View.draw(View.java:6274)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.drawChild(ViewGroup.java:1526)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.drawChild(ViewGroup.java:1524)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.View.draw(View.java:6277)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.widget.FrameLayout.draw(FrameLayout.java:352)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.drawChild(ViewGroup.java:1526)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.drawChild(ViewGroup.java:1524)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.View.draw(View.java:6277)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.widget.FrameLayout.draw(FrameLayout.java:352)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1883)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewRoot.draw(ViewRoot.java:1332)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewRoot.performTraversals(ViewRoot.java:1097)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.view.ViewRoot.handleMessage(ViewRoot.java:1613)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.os.Handler.dispatchMessage(Handler.java:99)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.os.Looper.loop(Looper.java:123)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at android.app.ActivityThread.main(ActivityThread.java:4203)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at java.lang.reflect.Method.invokeNative(Native Method)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at java.lang.reflect.Method.invoke(Method.java:521)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
01-19 05:31:46.541: ERROR/AndroidRuntime(770): at dalvik.system.NativeStart.main(Native Method)
01-19 05:31:46.551: INFO/Process(583): Sending signal. PID: 770 SIG: 3
01-19 05:31:46.581: INFO/dalvikvm(770): threadid=7: reacting to signal 3
01-19 05:31:46.661: INFO/dalvikvm(770): Wrote stack trace to '/data/anr/traces.txt'
01-19 05:31:46.871: INFO/ARMAssembler(583): generated scanline__00000077:03515104_00000000_00000000 [ 27 ipp] (41 ins) at [0x2c69c8:0x2c6a6c] in 973448 ns
01-19 05:31:46.911: INFO/ARMAssembler(583): generated scanline__00000077:03515104_00001001_00000000 [ 64 ipp] (84 ins) at [0x2c6a70:0x2c6bc0] in 1985378 ns
01-19 05:31:49.881: INFO/Process(770): Sending signal. PID: 770 SIG: 9
01-19 05:31:49.931: INFO/ActivityManager(583): Process pro.googlemapp (pid 770) has died.
01-19 05:31:49.941: WARN/GpsLocationProvider(583): Unneeded remove listener for uid 1000
01-19 05:31:49.941: DEBUG/GpsLocationProvider(583): stopNavigating
01-19 05:31:49.951: INFO/WindowManager(583): WIN DEATH: Window{438891c0 pro.googlemapp/pro.googlemapp.LocationActivity paused=false}
01-19 05:31:50.111: WARN/UsageStats(583): Unexpected resume of com.android.launcher while already resumed in pro.googlemapp
01-19 05:31:50.200: WARN/InputManagerService(583): Got RemoteException sending setActive(false) notification to pid 770 uid 10025
the way you construct the MyLocationOverlay might have some problem.
MyLocationOverlay mylocationOverlay = new MyLocationOverlay(this, mapView);
according to the google code api you need to pass a context and a mapview param.
and then put these code after that
mylocationOverlay.enableMyLocation();
mapView.getOverlays().add(locationOverlay);
also put
mylocationOverlay.enableMyLocation(); in the onResume() method
Hope this could help you.
The GeoPoint "p" in the MyLocationOverlay is null. When you replay "GeoPoint initGeoPoint" with "p" you can solve this problem.
This is something which might help you in sloving your byg:
In your logs look at this line 01-19 05:31:46.541: ERROR/AndroidRuntime(770): at pro.googlemapp.LocationActivity$MyLocationOverlay.draw(LocationActivity.java:101)
This refers to the GeoPoint p. At the beginning you set the value of p to null (as "asdf" says) and never change its value to a GeoPoint and that is why you get java.lang.NullPointerException.
For example you can set the value of p like this: p = new GeoPoint(19240000,-99120000); and of course this must happen before this line mapView.getProjection().toPixels(p, myScreenCoords); of your code.
Good luck
This is because Geopoint p value is null in class MyLocationListener. So when you called mapView.getProjection().toPixels(p, myScreenCoords); because p is null it is unable to convert toPixels and throws Exception. You can overcome on this by just declare your GeoPoint p as static in your LocationActivity.
来源：https://stackoverflow.com/questions/2091127/marking-current-location-on-map-android