我正在尝试启动一个地图活动，它可以获取当前的gps位置。按下按钮时它工作正常，直到我决定为用户添加一项功能，如果它被禁用，则打开他的gps。我使用了在Google上找到的代码片段，它使用了某种处理程序类。它不起作用，我一直在我的错误日志中看到它，所以我把它拿出来了。但是只要按下按钮，程序就会继续返回空指针异常。
我的问题是“我如何让程序重新启动以前的地图活动，如果可能的话，我如何进行gps检查
这是我的logcat
08-05 08:24:50.411: E/AndroidRuntime(17838): FATAL EXCEPTION: main
08-05 08:24:50.411: E/AndroidRuntime(17838): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.g6.georeminderv3/com.g6.georeminderv3.CheckInActivity}: java.lang.NullPointerException
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1872)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1893)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.app.ActivityThread.access$1500(ActivityThread.java:135)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1054)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.os.Handler.dispatchMessage(Handler.java:99)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.os.Looper.loop(Looper.java:150)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.app.ActivityThread.main(ActivityThread.java:4385)
08-05 08:24:50.411: E/AndroidRuntime(17838): at java.lang.reflect.Method.invokeNative(Native Method)
08-05 08:24:50.411: E/AndroidRuntime(17838): at java.lang.reflect.Method.invoke(Method.java:507)
08-05 08:24:50.411: E/AndroidRuntime(17838): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)
08-05 08:24:50.411: E/AndroidRuntime(17838): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
08-05 08:24:50.411: E/AndroidRuntime(17838): at dalvik.system.NativeStart.main(Native Method)
08-05 08:24:50.411: E/AndroidRuntime(17838): Caused by: java.lang.NullPointerException
08-05 08:24:50.411: E/AndroidRuntime(17838): at com.google.android.maps.ItemizedOverlay.populate(ItemizedOverlay.java:312)
08-05 08:24:50.411: E/AndroidRuntime(17838): at com.g6.georeminderv3.OverlayItems.addOverlay(OverlayItems.java:22)
08-05 08:24:50.411: E/AndroidRuntime(17838): at com.g6.georeminderv3.CheckInActivity.onCreate(CheckInActivity.java:100)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1072)
08-05 08:24:50.411: E/AndroidRuntime(17838): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1836)
08-05 08:24:50.411: E/AndroidRuntime(17838): ... 11 more
08-05 08:24:52.322: D/Process(17838): killProcess, pid=17838
08-05 08:24:52.322: D/Process(17838): dalvik.system.VMStack.getThreadStackTrace(Native Method)
08-05 08:24:52.322: D/Process(17838): java.lang.Thread.getStackTrace(Thread.java:745)
08-05 08:24:52.322: D/Process(17838): android.os.Process.killProcess(Process.java:797)
08-05 08:24:52.322: D/Process(17838): com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:108)
08-05 08:24:52.322: D/Process(17838): java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:854)
08-05 08:24:52.322: D/Process(17838): java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:851)
08-05 08:24:52.322: D/Process(17838): dalvik.system.NativeStart.main(Native Method)
08-05 08:24:52.322: I/Process(17838): Sending signal. PID: 17838 SIG: 9
这是我开始签入活动的主要活动
public class MainActivity extends Activity implements OnClickListener {
ImageButton add, settings, checkIn;
ListView list;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
findviews();
populateListView();
settings.setOnClickListener(this);
add.setOnClickListener(this);
checkIn.setOnClickListener(this);
}
private void populateListView() {
DatabaseHandler db = new DatabaseHandler(this);
// start here
SQLiteDatabase database = db.getReadableDatabase();
Log.d(DatabaseHandler.TAG, DatabaseHandler.actionsSelectQuery);
String[] columns = new String[] { DatabaseHandler.KEY_ACTIONS_ID,
DatabaseHandler.KEY_ACTIONS_TITLE,
DatabaseHandler.KEY_ACTIONS_PLACE_NAME,
DatabaseHandler.KEY_ACTIONS_TIME,
DatabaseHandler.KEY_ACTIONS_DATE };
// Cursor cursor = database.rawQuery(db.actionsSelectQuery, null);
Cursor cursor = database.query(DatabaseHandler.TABLE_ACTIONS, columns,
null, null, null, null, DatabaseHandler.KEY_ACTIONS_ID + " DESC");
String[] from = new String[] { DatabaseHandler.KEY_ACTIONS_TITLE,
DatabaseHandler.KEY_ACTIONS_PLACE_NAME,
DatabaseHandler.KEY_ACTIONS_TIME,
DatabaseHandler.KEY_ACTIONS_DATE };
int[] to = { R.id.title_text, R.id.place_text, R.id.time_text,
R.id.date_text };
@SuppressWarnings("deprecation")
SimpleCursorAdapter listAdapter = new SimpleCursorAdapter(
MainActivity.this, R.layout.action_list_layout, cursor, from,
to);
list.setAdapter(listAdapter);
Log.d(DatabaseHandler.TAG, "list view created");
// mySQLiteAdapter.close();
}
private void findviews() {
settings = (ImageButton) findViewById(R.id.settings);
add = (ImageButton) findViewById(R.id.add_reminder);
checkIn = (ImageButton) findViewById(R.id.check_in);
list = (ListView) findViewById(R.id.action_list_view);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
//add fav manager here
return true;
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.settings:
startActivity(new Intent(MainActivity.this, SettingsActivity.class));
break;
case R.id.add_reminder:
startActivity(new Intent(MainActivity.this, AddReminder.class));
MainActivity.this.finish();
break;
case R.id.check_in:
startActivity(new Intent(MainActivity.this, CheckInActivity.class));
break;
}
}
}
这是我的checkinactivity
public class CheckInActivity extends MapActivity {
private int place_longitude;
private int place_latitude;
Button save;
EditText chkInPlaceName;
String chkSavePlaceName,setPlongString,setPlatString;
TextView setPlong,setPlat;
GeoPoint point;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_check_in);
MapView mapView = (MapView) findViewById(R.id.mapview);
final MapController controller = mapView.getController();
LocationManager manager = (LocationManager) this
.getSystemService(LOCATION_SERVICE);
LocationListener listener = new LocationListener() {
@Override
public void onStatusChanged(String provider, int status,
Bundle extras) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onLocationChanged(Location location) {
setPlace_latitude((int) location.getLatitude());
setPlace_longitude((int) location.getLongitude());
point = new GeoPoint(getPlace_latitude(), getPlace_longitude());
controller.setCenter(point);
}
};
manager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 900, 300,
listener);
// TODO 900 is the number of seconds to triger a location updat set it
// up in the prefrence
// TODO 300 is the minimum distace in metres to trigger a location up.
// set it up in settings
// pinin starts here
List<Overlay> mapOverlays = mapView.getOverlays();
Drawable drawable = this.getResources().getDrawable(R.drawable.pin);
OverlayItems itemizedoverlay = new OverlayItems(drawable, this);
setPlat = (TextView) findViewById(R.id.set_plat);
setPlong = (TextView) findViewById(R.id.set_plong);
setPlat.setText("Latitude: " + getPlace_latitude());
setPlong.setText("Longitude: " + getPlace_longitude());
OverlayItem overlayitem = new OverlayItem(point, "Hello World!",
"I'm here!");
itemizedoverlay.addOverlay(overlayitem);
mapOverlays.add(itemizedoverlay);
save = (Button) findViewById(R.id.save_btn);
save.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
chkInPlaceName = (EditText) findViewById(R.id.check_in_place_name);
chkSavePlaceName = chkInPlaceName.getText().toString();
if (chkSavePlaceName.equals("")) {
Toast.makeText(CheckInActivity.this, "Enter Place name",
Toast.LENGTH_SHORT).show();
} else {
DatabaseHandler db = new DatabaseHandler(
CheckInActivity.this);
/**
* CRUD Operations
* */
// Inserting Action
db.addPlace(new Places(chkSavePlaceName,
getPlace_latitude(), getPlace_longitude()));
startActivity(new Intent(CheckInActivity.this,
MainActivity.class));
CheckInActivity.this.finish();
}
}
});
// pinning ends here
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.check_in, menu);
return true;
}
@Override
protected boolean isRouteDisplayed() {
return false;
}
public int getPlace_longitude() {
return place_longitude;
}
public void setPlace_longitude(int place_longitude) {
this.place_longitude = place_longitude;
}
public int getPlace_latitude() {
return place_latitude;
}
public void setPlace_latitude(int place_latitude) {
this.place_latitude = place_latitude;
}
}
这是叠加层
public class OverlayItems extends ItemizedOverlay<OverlayItem>{
Context mContext;
private ArrayList<OverlayItem> mOverlays = new ArrayList<OverlayItem>();
public void addOverlay(OverlayItem overlay) {
mOverlays.add(overlay);
populate();
}
public OverlayItems(Drawable defaultMarker, Context context) {
super(boundCenterBottom(defaultMarker));
mContext = context;
}
@Override
protected OverlayItem createItem(int i) {
return mOverlays.get(i);
}
@Override
public int size() {
return mOverlays.size();
}
@Override
protected boolean onTap(int index) {
OverlayItem item = mOverlays.get(index);
AlertDialog.Builder dialog = new AlertDialog.Builder(mContext);
dialog.setTitle(item.getTitle());
dialog.setMessage(item.getSnippet());
dialog.show();
return true;
}
}
答案 0 :(得分：0)
问题是因为您的Point为null。您应该验证该点是否与null不同，因为当您执行OverlayItem overlayitem = new OverlayItem时（点，“Hello World！”， “我在这！”）;该点为null，onCreate在onLocationChanged之前被调用。
对此评论感到抱歉，这是我在这里的第一天。
答案 1 :(得分：0)
这是我的答案，但我只能猜测，因为我无法对您的代码进行完整的调试。
在CheckInActivity位于中间某处的onCreate(...)中，您可以创建一个OverlayItem对象：
OverlayItem overlayitem = new OverlayItem(point, "Hello World!", "I'm here!");
参数 point 是一个成员变量，GeoPoint。在LocationManager分配onLocationChanged()处的第一个值之前，尚未初始化此变量。由于LocationManager可能需要一段时间才能获取该位置并将其分配给GeoPoint，因此您之前可能会执行创建OverlayItem的行，因此point仍为null。
我的猜测，请通过适当的调试来检查。