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問題：無法從MainActiviy> MapActivity的按鈕單擊開始活動。Android開發中的開始活動（NullPointerException）出錯
P/s：我按照這個地圖教程並更改類名並將所有元素複製到我的項目工作區。 This Tutorial
按鈕偵聽
public void onClick(View v) {
Intent intent = new Intent(getApplicationContext(),
MapActivity.class);
startActivity(intent);}
logcat的：
07-31 02:22:58.267: E/AndroidRuntime(20784): FATAL EXCEPTION: main
07-31 02:22:58.267: E/AndroidRuntime(20784): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fa.financeassistant/com.fa.financeassistant.MapActivity}: java.lang.NullPointerException
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2308)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.ActivityThread.access$600(ActivityThread.java:153)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.os.Handler.dispatchMessage(Handler.java:99)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.os.Looper.loop(Looper.java:137)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.ActivityThread.main(ActivityThread.java:5227)
07-31 02:22:58.267: E/AndroidRuntime(20784): at java.lang.reflect.Method.invokeNative(Native Method)
07-31 02:22:58.267: E/AndroidRuntime(20784): at java.lang.reflect.Method.invoke(Method.java:511)
07-31 02:22:58.267: E/AndroidRuntime(20784): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
07-31 02:22:58.267: E/AndroidRuntime(20784): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
07-31 02:22:58.267: E/AndroidRuntime(20784): at dalvik.system.NativeStart.main(Native Method)
07-31 02:22:58.267: E/AndroidRuntime(20784): Caused by: java.lang.NullPointerException
07-31 02:22:58.267: E/AndroidRuntime(20784): at com.fa.financeassistant.MapActivity.onCreate(MapActivity.java:46)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.Activity.performCreate(Activity.java:5104)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-31 02:22:58.267: E/AndroidRuntime(20784): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2262)
07-31 02:22:58.267: E/AndroidRuntime(20784): ... 11 more
我MapActivity類
package com.fa.financeassistant;
import java.util.ArrayList;
import android.R.array;
import android.app.ActionBar;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.widget.ArrayAdapter;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
public class MapActivity extends Activity {
private final String TAG = getClass().getSimpleName();
private GoogleMap mMap;
private String[] places;
private LocationManager locationManager;
private Location loc;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mapactivity);
initCompo();
places = getResources().getStringArray(R.array.places);
currentLocation();
final ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);
actionBar.setListNavigationCallbacks(ArrayAdapter.createFromResource(
this, R.array.places, android.R.layout.simple_list_item_1),
new ActionBar.OnNavigationListener() {
@Override
public boolean onNavigationItemSelected(int itemPosition,
long itemId) {
Log.e(TAG,
places[itemPosition].toLowerCase().replace("-",
"_"));
if (loc != null) {
mMap.clear();
new GetPlaces(MapActivity.this,
places[itemPosition].toLowerCase().replace(
"-", "_").replace(" ", "_")).execute();
}
return true;
}
});
}
private class GetPlaces extends AsyncTask<Void, Void, ArrayList<Place>> {
private ProgressDialog dialog;
private Context context;
private String places;
public GetPlaces(Context context, String places) {
this.context = context;
this.places = places;
}
@Override
protected void onPostExecute(ArrayList<Place> result) {
super.onPostExecute(result);
if (dialog.isShowing()) {
dialog.dismiss();
}
for (int i = 0; i < result.size(); i++) {
mMap.addMarker(new MarkerOptions()
.title(result.get(i).getName())
.position(
new LatLng(result.get(i).getLatitude(), result
.get(i).getLongitude()))
.icon(BitmapDescriptorFactory
.fromResource(R.drawable.pin))
.snippet(result.get(i).getVicinity()));
}
CameraPosition cameraPosition = new CameraPosition.Builder()
.target(new LatLng(result.get(0).getLatitude(), result
.get(0).getLongitude())) // Sets the center of the map to
// Mountain View
.zoom(14) // Sets the zoom
.tilt(30) // Sets the tilt of the camera to 30 degrees
.build(); // Creates a CameraPosition from the builder
mMap.animateCamera(CameraUpdateFactory
.newCameraPosition(cameraPosition));
}
@Override
protected void onPreExecute() {
super.onPreExecute();
dialog = new ProgressDialog(context);
dialog.setCancelable(false);
dialog.setMessage("Loading");
dialog.isIndeterminate();
dialog.show();
}
@Override
protected ArrayList<Place> doInBackground(Void... arg0) {
PlacesService service = new PlacesService(
"AIzaSyBquLw9vJPDHAZO8kzKw6ft0bPxsgBmblg");
ArrayList<Place> findPlaces = service.findPlaces(loc.getLatitude(), // 28.632808
loc.getLongitude(), places); // 77.218276
for (int i = 0; i < findPlaces.size(); i++) {
Place placeDetail = findPlaces.get(i);
Log.e(TAG, "places : " + placeDetail.getName());
}
return findPlaces;
}
}
private void initCompo() {
mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map))
.getMap();
}
private void currentLocation() {
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
String provider = locationManager
.getBestProvider(new Criteria(), false);
Location location = locationManager.getLastKnownLocation(provider);
if (location == null) {
locationManager.requestLocationUpdates(provider, 0, 0, listener);
} else {
loc = location;
new GetPlaces(MapActivity.this, places[0].toLowerCase().replace(
"-", "_")).execute();
Log.e(TAG, "location : " + location);
}
}
private LocationListener listener = new LocationListener() {
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onLocationChanged(Location location) {
Log.e(TAG, "location update : " + location);
loc = location;
locationManager.removeUpdates(listener);
}
};
}
SOLUTION：除了下面給出的答案。我通過刪除這一行來應用快速修復，並像魅力一樣工作！感謝所有幫助過我的人。祝你有美好的一天:)
android:theme="@style/Theme.NoTitle"
什麼是第46行？ – codeMagic
確保'getActionBar（）'不返回'null'。或者考慮到它可以返回null。 – MAV
如果我已經計算正確，它是'actionBar.setNavigationMode（ActionBar.NAVIGATION_MODE_LIST）;' - 在這一行上放置一個斷點。 ActionBar是否爲空？ – Simon