嘿，我是 android 新手，我正在处理一个面向地图的项目，现在我在触摸覆盖项目时遇到问题，它在 log-cat 中显示空指针异常，我不明白这是什么意思。这里我有两个类MyPlacemapActivity 和 AddItemizedOverlay 有人请帮我解决这个问题，这是我的课程代码
AddItemizedOverlay.java
public class AddItemizedOverlay extends ItemizedOverlay<OverlayItem> {
private ArrayList<OverlayItem> mapOverlays = new ArrayList<OverlayItem>();
private Context context;
String reference;
private String username;
String p_u_name;
public AddItemizedOverlay(Drawable defaultMarker) {
super(boundCenterBottom(defaultMarker));
}
public AddItemizedOverlay(Drawable defaultMarker, Context context) {
this(defaultMarker);
this.context = context;
}
public AddItemizedOverlay(Drawable defaultMarker, Context context,String StringData) {
this(defaultMarker);
this.context = context;
this.username=StringData;
System.out.println("AdditemizedOverlay:got username:"+username +StringData);
}
@Override
public boolean onTouchEvent(MotionEvent event, MapView mapView)
{
if (event.getAction() == 1) {
GeoPoint geopoint = mapView.getProjection().fromPixels(
(int) event.getX(),
(int) event.getY());
}
return false;
}
@Override
protected OverlayItem createItem(int i) {
return mapOverlays.get(i);
}
@Override
public int size() {
return mapOverlays.size();
}
@Override
protected boolean onTap(int index) {
OverlayItem item = mapOverlays.get(index);
AlertDialog.Builder dialog = new AlertDialog.Builder(this.context);
reference = item.getSnippet();
username = item.getTitle();
dialog.setTitle("");
dialog.setMessage("Do you want ot park here ?");
System.out.println("Inside Additemized:"+reference+username);
dialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
SharedPreferences prefs = context.getSharedPreferences("myprefs", 0);
SharedPreferences.Editor editor =prefs.edit();
editor.putString("KEY_REFERENCE", reference);
editor.putString("KEY_USERNAME", username);
editor.commit();
Intent intent = new Intent(context, SinglePlaceActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(intent);
}
})
.setNegativeButton("No",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id) {
// if this button is clicked, just close
// the dialog box and do nothing
dialog.cancel();
// MainActivity.this.finish();
}
});
dialog.show();
return true;
}
public void addOverlay(OverlayItem overlay) {
mapOverlays.add(overlay);
}
public void populateNow(){
this.populate();
}
}
MyPlacemapActivity.java
public class MyPlacemapActivity extends MapActivity {
// Nearest places
PlacesList nearPlaces;
// Map view
MapView mapView;
// Map overlay items
List<Overlay> mapOverlays;
AddItemizedOverlay itemizedOverlay;
MyItemizedOverlay myitemizedoverlay;
FindItemizedOverlay finditemizedoverlay;
GeoPoint geoPoint;
// Map controllers
MapController mc;
Drawable defaultMarker,drawable;
double latitude;
double longitude;
OverlayItem overlayitem;
String p_u_name;
String type,keyword;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.map_places);
SharedPreferences prefs = getSharedPreferences("myprefs", 0);
p_u_name = prefs.getString("KEY_USERNAME", "");
Intent i = getIntent();
// Users current geo location
String user_latitude = i.getStringExtra("user_latitude");
String user_longitude = i.getStringExtra("user_longitude");
type = i.getExtras().getString("KEY_TYPES");
keyword =i.getExtras().getString("KEY_KEYWORD");
System.out.println("sarath"+user_latitude + user_longitude + type);
// Nearplaces list
nearPlaces = (PlacesList) i.getSerializableExtra("near_places");
mapView = (MapView) findViewById(R.id.mapView);
mapView.setBuiltInZoomControls(true);
mapOverlays = mapView.getOverlays();
// Geopoint to place on map
geoPoint = new GeoPoint((int) (Double.parseDouble(user_latitude) * 1E6),(int) (Double.parseDouble(user_longitude) * 1E6));
// Drawable marker icon
Drawable drawable_user = this.getResources().getDrawable(R.drawable.mark_red);
myitemizedoverlay = new MyItemizedOverlay(drawable_user, this);
// Map overlay item
overlayitem = new OverlayItem(geoPoint, "Your Location","That is you!");
myitemizedoverlay.addOverlay(overlayitem);
mapOverlays.add(myitemizedoverlay);
myitemizedoverlay.populateNow();
System.out.println("keyword:"+keyword+"type:"+type);
//----------------------------------------------------------------------------------------------------------
// Drawable marker icon
if(type.equalsIgnoreCase("gas_station")&&keyword.equalsIgnoreCase("gas_station")){
drawable= this.getResources().getDrawable(R.drawable.mark_gasstation);
finditemizedoverlay = new FindItemizedOverlay(drawable);
mc = mapView.getController();
// These values are used to get map boundary area
// The area where you can see all the markers on screen
int minLat = Integer.MAX_VALUE;
int minLong = Integer.MAX_VALUE;
int maxLat = Integer.MIN_VALUE;
int maxLong = Integer.MIN_VALUE;
// check for null in case it is null
if (nearPlaces.results != null) {
// loop through all the places
for (Place mplace : nearPlaces.results) {
latitude = mplace.geometry.location.lat; // latitude
longitude = mplace.geometry.location.lng; // longitude
// Geopoint to place on map
geoPoint = new GeoPoint((int) (latitude * 1E6),
(int) (longitude * 1E6));
// Map overlay item
overlayitem = new OverlayItem(geoPoint,p_u_name,mplace.reference);
finditemizedoverlay.addOverlay(overlayitem);
// calculating map boundary area
minLat = (int) Math.min( geoPoint.getLatitudeE6(), minLat );
minLong = (int) Math.min( geoPoint.getLongitudeE6(), minLong);
maxLat = (int) Math.max( geoPoint.getLatitudeE6(), maxLat );
maxLong = (int) Math.max( geoPoint.getLongitudeE6(), maxLong );
}
mapOverlays.add(finditemizedoverlay);
// showing all overlay items
finditemizedoverlay.populateNow();
}
// Adjusting the zoom level so that you can see all the markers on map
mapView.getController().zoomToSpan(Math.abs( minLat - maxLat ), Math.abs( minLong - maxLong ));
// Showing the center of the map
mc.animateTo(new GeoPoint((maxLat + minLat)/2, (maxLong + minLong)/2 ));
mapView.postInvalidate();
}
else if(type.equalsIgnoreCase("shopping_mall")&&keyword.equalsIgnoreCase("shopping_mall")){
drawable= this.getResources().getDrawable(R.drawable.mark_shopping);
finditemizedoverlay = new FindItemizedOverlay(drawable);
mc = mapView.getController();
// These values are used to get map boundary area
// The area where you can see all the markers on screen
int minLat = Integer.MAX_VALUE;
int minLong = Integer.MAX_VALUE;
int maxLat = Integer.MIN_VALUE;
int maxLong = Integer.MIN_VALUE;
// check for null in case it is null
if (nearPlaces.results != null) {
// loop through all the places
for (Place mplace : nearPlaces.results) {
latitude = mplace.geometry.location.lat; // latitude
longitude = mplace.geometry.location.lng; // longitude
// Geopoint to place on map
geoPoint = new GeoPoint((int) (latitude * 1E6),
(int) (longitude * 1E6));
// Map overlay item
overlayitem = new OverlayItem(geoPoint,p_u_name,mplace.reference);
finditemizedoverlay.addOverlay(overlayitem);
// calculating map boundary area
minLat = (int) Math.min( geoPoint.getLatitudeE6(), minLat );
minLong = (int) Math.min( geoPoint.getLongitudeE6(), minLong);
maxLat = (int) Math.max( geoPoint.getLatitudeE6(), maxLat );
maxLong = (int) Math.max( geoPoint.getLongitudeE6(), maxLong );
}
mapOverlays.add(finditemizedoverlay);
// showing all overlay items
finditemizedoverlay.populateNow();
}
// Adjusting the zoom level so that you can see all the markers on map
mapView.getController().zoomToSpan(Math.abs( minLat - maxLat ), Math.abs( minLong - maxLong ));
// Showing the center of the map
mc.animateTo(new GeoPoint((maxLat + minLat)/2, (maxLong + minLong)/2 ));
mapView.postInvalidate();
}
else if(type.equalsIgnoreCase("restaurant")&&keyword.equalsIgnoreCase("restaurant")){
drawable= this.getResources().getDrawable(R.drawable.mark_restaurant_blue);
finditemizedoverlay = new FindItemizedOverlay(drawable);
mc = mapView.getController();
// These values are used to get map boundary area
// The area where you can see all the markers on screen
int minLat = Integer.MAX_VALUE;
int minLong = Integer.MAX_VALUE;
int maxLat = Integer.MIN_VALUE;
int maxLong = Integer.MIN_VALUE;
// check for null in case it is null
if (nearPlaces.results != null) {
// loop through all the places
for (Place mplace : nearPlaces.results) {
latitude = mplace.geometry.location.lat; // latitude
longitude = mplace.geometry.location.lng; // longitude
// Geopoint to place on map
geoPoint = new GeoPoint((int) (latitude * 1E6),
(int) (longitude * 1E6));
// Map overlay item
overlayitem = new OverlayItem(geoPoint,p_u_name,mplace.reference);
finditemizedoverlay.addOverlay(overlayitem);
// calculating map boundary area
minLat = (int) Math.min( geoPoint.getLatitudeE6(), minLat );
minLong = (int) Math.min( geoPoint.getLongitudeE6(), minLong);
maxLat = (int) Math.max( geoPoint.getLatitudeE6(), maxLat );
maxLong = (int) Math.max( geoPoint.getLongitudeE6(), maxLong );
}
mapOverlays.add(finditemizedoverlay);
// showing all overlay items
finditemizedoverlay.populateNow();
}
// Adjusting the zoom level so that you can see all the markers on map
mapView.getController().zoomToSpan(Math.abs( minLat - maxLat ), Math.abs( minLong - maxLong ));
// Showing the center of the map
mc.animateTo(new GeoPoint((maxLat + minLat)/2, (maxLong + minLong)/2 ));
mapView.postInvalidate();
}
else if(type.equalsIgnoreCase("parking")&&keyword.equalsIgnoreCase("garage parking")){
drawable= this.getResources().getDrawable(R.drawable.mark_blue);
itemizedOverlay = new AddItemizedOverlay(drawable);
mc = mapView.getController();
// These values are used to get map boundary area
// The area where you can see all the markers on screen
int minLat = Integer.MAX_VALUE;
int minLong = Integer.MAX_VALUE;
int maxLat = Integer.MIN_VALUE;
int maxLong = Integer.MIN_VALUE;
// check for null in case it is null
if (nearPlaces.results != null) {
// loop through all the places
for (Place mplace : nearPlaces.results) {
latitude = mplace.geometry.location.lat; // latitude
longitude = mplace.geometry.location.lng; // longitude
// Geopoint to place on map
geoPoint = new GeoPoint((int) (latitude * 1E6),
(int) (longitude * 1E6));
// Map overlay item
overlayitem = new OverlayItem(geoPoint,p_u_name,mplace.reference);
System.out.println("inside mymap:"+mplace.reference+p_u_name);
itemizedOverlay.addOverlay(overlayitem);
// calculating map boundary area
minLat = (int) Math.min( geoPoint.getLatitudeE6(), minLat );
minLong = (int) Math.min( geoPoint.getLongitudeE6(), minLong);
maxLat = (int) Math.max( geoPoint.getLatitudeE6(), maxLat );
maxLong = (int) Math.max( geoPoint.getLongitudeE6(), maxLong );
}
mapOverlays.add(itemizedOverlay);
// showing all overlay items
itemizedOverlay.populateNow();
}
// Adjusting the zoom level so that you can see all the markers on map
mapView.getController().zoomToSpan(Math.abs( minLat - maxLat ), Math.abs( minLong - maxLong ));
// Showing the center of the map
mc.animateTo(new GeoPoint((maxLat + minLat)/2, (maxLong + minLong)/2 ));
mapView.postInvalidate();
}
else if(type.equalsIgnoreCase("parking")&&keyword.equalsIgnoreCase("street parking")){
drawable= this.getResources().getDrawable(R.drawable.mark_blue);
itemizedOverlay = new AddItemizedOverlay(drawable);
mc = mapView.getController();
// These values are used to get map boundary area
// The area where you can see all the markers on screen
int minLat = Integer.MAX_VALUE;
int minLong = Integer.MAX_VALUE;
int maxLat = Integer.MIN_VALUE;
int maxLong = Integer.MIN_VALUE;
// check for null in case it is null
if (nearPlaces.results != null) {
// loop through all the places
for (Place mplace : nearPlaces.results) {
latitude = mplace.geometry.location.lat; // latitude
longitude = mplace.geometry.location.lng; // longitude
// Geopoint to place on map
geoPoint = new GeoPoint((int) (latitude * 1E6),
(int) (longitude * 1E6));
// Map overlay item
overlayitem = new OverlayItem(geoPoint,p_u_name,mplace.reference);
System.out.println("inside mymap:"+mplace.reference +p_u_name);
itemizedOverlay.addOverlay(overlayitem);
// calculating map boundary area
minLat = (int) Math.min( geoPoint.getLatitudeE6(), minLat );
minLong = (int) Math.min( geoPoint.getLongitudeE6(), minLong);
maxLat = (int) Math.max( geoPoint.getLatitudeE6(), maxLat );
maxLong = (int) Math.max( geoPoint.getLongitudeE6(), maxLong );
}
mapOverlays.add(itemizedOverlay);
// showing all overlay items
itemizedOverlay.populateNow();
}
// Adjusting the zoom level so that you can see all the markers on map
mapView.getController().zoomToSpan(Math.abs( minLat - maxLat ), Math.abs( minLong - maxLong ));
// Showing the center of the map
mc.animateTo(new GeoPoint((maxLat + minLat)/2, (maxLong + minLong)/2 ));
mapView.postInvalidate();
}
else
{
AlertDialog.Builder builder = new AlertDialog.Builder(MyPlacemapActivity.this);
builder.setTitle("Connection Error.");
builder.setMessage("Try again?.")
.setCancelable(false)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
Intent u = new Intent(getApplicationContext(),Find_TabActivity.class);
startActivity(u);
dialog.dismiss();
}
});
AlertDialog alert = builder.create();
alert.show();
}
}
@Override
protected boolean isRouteDisplayed() {
return false;
}
}