我是韩国的大学生。 我用翻译器。 请原谅我不柔软。 编写代码，提问时无法解决问题 请帮助我。
下面的代码很简单，唯一的目标是从MainActivity.java导航到Mian2Activity.java。但是，我一直在很多教程中寻找解决方案，但我确实没有得到错了...
这是Main2Activity代码
public class Main2Activity extends AppCompatActivity
implements OnMapReadyCallback,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener,
LocationListener {
private GoogleApiClient mGoogleApiClient = null;
private GoogleMap mGoogleMap = null;
private Marker currentMarker = null;
private static final String TAG = "googlemap_example";
private static final int GPS_ENABLE_REQUEST_CODE = 2001;
private static final int PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION = 2002;
private static final int UPDATE_INTERVAL_MS = 1000; // 1초
private static final int FASTEST_UPDATE_INTERVAL_MS = 500; // 0.5초
private AppCompatActivity mActivity;
boolean askPermissionOnceAgain = false;
boolean mRequestingLocationUpdates = false;
Location mCurrentLocatiion;
boolean mMoveMapByUser = true;
boolean mMoveMapByAPI = true;
LatLng currentPosition;
LocationRequest locationRequest = new LocationRequest()
.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY)
.setInterval(UPDATE_INTERVAL_MS)
.setFastestInterval(FASTEST_UPDATE_INTERVAL_MS);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,
WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
setContentView(R.layout.activity_main);
Log.d(TAG, "onCreate");
mActivity = this;
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
MapFragment mapFragment = (MapFragment) getFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
@Override
public void onResume() {
super.onResume();
if (mGoogleApiClient.isConnected()) {
Log.d(TAG, "onResume : call startLocationUpdates");
if (!mRequestingLocationUpdates) startLocationUpdates();
}
//앱 정보에서 퍼미션을 허가했는지를 다시 검사해봐야 한다.
if (askPermissionOnceAgain) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
askPermissionOnceAgain = false;
checkPermissions();
}
}
}
private void startLocationUpdates() {
if (!checkLocationServicesStatus()) {
Log.d(TAG, "startLocationUpdates : call showDialogForLocationServiceSetting");
showDialogForLocationServiceSetting();
}else {
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED
&& ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
Log.d(TAG, "startLocationUpdates : 퍼미션 안가지고 있음");
return;
}
Log.d(TAG, "startLocationUpdates : call FusedLocationApi.requestLocationUpdates");
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, locationRequest, this);
mRequestingLocationUpdates = true;
mGoogleMap.setMyLocationEnabled(true);
}
}
private void stopLocationUpdates() {
Log.d(TAG,"stopLocationUpdates : LocationServices.FusedLocationApi.removeLocationUpdates");
LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
mRequestingLocationUpdates = false;
}
@Override
public void onMapReady(GoogleMap googleMap) {
Log.d(TAG, "onMapReady :");
mGoogleMap = googleMap;
//런타임 퍼미션 요청 대화상자나 GPS 활성 요청 대화상자 보이기전에
//지도의 초기위치를 서울로 이동
setDefaultLocation();
//mGoogleMap.getUiSettings().setZoomControlsEnabled(false);
mGoogleMap.getUiSettings().setMyLocationButtonEnabled(true);
mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(15));
mGoogleMap.setOnMyLocationButtonClickListener(new GoogleMap.OnMyLocationButtonClickListener(){
@Override
public boolean onMyLocationButtonClick() {
Log.d( TAG, "onMyLocationButtonClick : 위치에 따른 카메라 이동 활성화");
mMoveMapByAPI = true;
return true;
}
});
mGoogleMap.setOnMapClickListener(new GoogleMap.OnMapClickListener() {
@Override
public void onMapClick(LatLng latLng) {
Log.d( TAG, "onMapClick :");
}
});
mGoogleMap.setOnCameraMoveStartedListener(new GoogleMap.OnCameraMoveStartedListener() {
@Override
public void onCameraMoveStarted(int i) {
if (mMoveMapByUser == true && mRequestingLocationUpdates){
Log.d(TAG, "onCameraMove : 위치에 따른 카메라 이동 비활성화");
mMoveMapByAPI = false;
}
mMoveMapByUser = true;
}
});
mGoogleMap.setOnCameraMoveListener(new GoogleMap.OnCameraMoveListener() {
@Override
public void onCameraMove() {
}
});
}
@Override
public void onLocationChanged(Location location) {
currentPosition
= new LatLng( location.getLatitude(), location.getLongitude());
Log.d(TAG, "onLocationChanged : ");
String markerTitle = getCurrentAddress(currentPosition);
String markerSnippet = "위도:" + String.valueOf(location.getLatitude())
+ " 경도:" + String.valueOf(location.getLongitude());
//현재 위치에 마커 생성하고 이동
setCurrentLocation(location, markerTitle, markerSnippet);
mCurrentLocatiion = location;
}
@Override
protected void onStart() {
if(mGoogleApiClient != null && mGoogleApiClient.isConnected() == false){
Log.d(TAG, "onStart: mGoogleApiClient connect");
mGoogleApiClient.connect();
}
super.onStart();
}
@Override
protected void onStop() {
if (mRequestingLocationUpdates) {
Log.d(TAG, "onStop : call stopLocationUpdates");
stopLocationUpdates();
}
if ( mGoogleApiClient.isConnected()) {
Log.d(TAG, "onStop : mGoogleApiClient disconnect");
mGoogleApiClient.disconnect();
}
super.onStop();
}
@Override
public void onConnected(Bundle connectionHint) {
if ( mRequestingLocationUpdates == false ) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
int hasFineLocationPermission = ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION);
if (hasFineLocationPermission == PackageManager.PERMISSION_DENIED) {
ActivityCompat.requestPermissions(mActivity,
new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION},
PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION);
} else {
Log.d(TAG, "onConnected : 퍼미션 가지고 있음");
Log.d(TAG, "onConnected : call startLocationUpdates");
startLocationUpdates();
mGoogleMap.setMyLocationEnabled(true);
}
}else{
Log.d(TAG, "onConnected : call startLocationUpdates");
startLocationUpdates();
mGoogleMap.setMyLocationEnabled(true);
}
}
}
@Override
public void onConnectionFailed(ConnectionResult connectionResult) {
Log.d(TAG, "onConnectionFailed");
setDefaultLocation();
}
@Override
public void onConnectionSuspended(int cause) {
Log.d(TAG, "onConnectionSuspended");
if (cause == CAUSE_NETWORK_LOST)
Log.e(TAG, "onConnectionSuspended(): Google Play services " +
"connection lost. Cause: network lost.");
else if (cause == CAUSE_SERVICE_DISCONNECTED)
Log.e(TAG, "onConnectionSuspended(): Google Play services " +
"connection lost. Cause: service disconnected");
}
public String getCurrentAddress(LatLng latlng) {
//지오코더... GPS를 주소로 변환
Geocoder geocoder = new Geocoder(this, Locale.getDefault());
List<Address> addresses;
try {
addresses = geocoder.getFromLocation(
latlng.latitude,
latlng.longitude,
1);
} catch (IOException ioException) {
//네트워크 문제
Toast.makeText(this, "지오코더 서비스 사용불가", Toast.LENGTH_LONG).show();
return "지오코더 서비스 사용불가";
} catch (IllegalArgumentException illegalArgumentException) {
Toast.makeText(this, "잘못된 GPS 좌표", Toast.LENGTH_LONG).show();
return "잘못된 GPS 좌표";
}
if (addresses == null || addresses.size() == 0) {
Toast.makeText(this, "주소 미발견", Toast.LENGTH_LONG).show();
return "주소 미발견";
} else {
Address address = addresses.get(0);
return address.getAddressLine(0).toString();
}
}
public boolean checkLocationServicesStatus() {
LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
return locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)
|| locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
}
public void setCurrentLocation(Location location, String markerTitle, String markerSnippet) {
mMoveMapByUser = false;
if (currentMarker != null) currentMarker.remove();
LatLng currentLatLng = new LatLng(location.getLatitude(), location.getLongitude());
MarkerOptions markerOptions = new MarkerOptions();
markerOptions.position(currentLatLng);
markerOptions.title(markerTitle);
markerOptions.snippet(markerSnippet);
markerOptions.draggable(true);
//구글맵의 디폴트 현재 위치는 파란색 동그라미로 표시
//마커를 원하는 이미지로 변경하여 현재 위치 표시하도록 수정 fix - 2017. 11.27
markerOptions.icon(BitmapDescriptorFactory.fromResource(R.mipmap.ic_launcher));
currentMarker = mGoogleMap.addMarker(markerOptions);
if ( mMoveMapByAPI ) {
Log.d( TAG, "setCurrentLocation : mGoogleMap moveCamera "
+ location.getLatitude() + " " + location.getLongitude() ) ;
// CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngZoom(currentLatLng, 15);
CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLng(currentLatLng);
mGoogleMap.moveCamera(cameraUpdate);
}
}
public void setDefaultLocation() {
mMoveMapByUser = false;
//디폴트 위치, Seoul
LatLng DEFAULT_LOCATION = new LatLng(37.56, 126.97);
String markerTitle = "위치정보 가져올 수 없음";
String markerSnippet = "위치 퍼미션과 GPS 활성 요부 확인하세요";
if (currentMarker != null) currentMarker.remove();
MarkerOptions markerOptions = new MarkerOptions();
markerOptions.position(DEFAULT_LOCATION);
markerOptions.title(markerTitle);
markerOptions.snippet(markerSnippet);
markerOptions.draggable(true);
markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED));
currentMarker = mGoogleMap.addMarker(markerOptions);
CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngZoom(DEFAULT_LOCATION, 15);
mGoogleMap.moveCamera(cameraUpdate);
}
//여기부터는 런타임 퍼미션 처리을 위한 메소드들
@TargetApi(Build.VERSION_CODES.M)
private void checkPermissions() {
boolean fineLocationRationale = ActivityCompat
.shouldShowRequestPermissionRationale(this,
Manifest.permission.ACCESS_FINE_LOCATION);
int hasFineLocationPermission = ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION);
if (hasFineLocationPermission == PackageManager
.PERMISSION_DENIED && fineLocationRationale)
showDialogForPermission("앱을 실행하려면 퍼미션을 허가하셔야합니다.");
else if (hasFineLocationPermission
== PackageManager.PERMISSION_DENIED && !fineLocationRationale) {
showDialogForPermissionSetting("퍼미션 거부 + Don't ask again(다시 묻지 않음) " +
"체크 박스를 설정한 경우로 설정에서 퍼미션 허가해야합니다.");
} else if (hasFineLocationPermission == PackageManager.PERMISSION_GRANTED) {
Log.d(TAG, "checkPermissions : 퍼미션 가지고 있음");
if ( mGoogleApiClient.isConnected() == false) {
Log.d(TAG, "checkPermissions : 퍼미션 가지고 있음");
mGoogleApiClient.connect();
}
}
}
@Override
public void onRequestPermissionsResult(int permsRequestCode,
@NonNull String[] permissions,
@NonNull int[] grantResults) {
if (permsRequestCode
== PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION && grantResults.length > 0) {
boolean permissionAccepted = grantResults[0] == PackageManager.PERMISSION_GRANTED;
if (permissionAccepted) {
if ( mGoogleApiClient.isConnected() == false) {
Log.d(TAG, "onRequestPermissionsResult : mGoogleApiClient connect");
mGoogleApiClient.connect();
}
} else {
checkPermissions();
}
}
}
@TargetApi(Build.VERSION_CODES.M)
private void showDialogForPermission(String msg) {
AlertDialog.Builder builder = new AlertDialog.Builder(Main2Activity.this);
builder.setTitle("알림");
builder.setMessage(msg);
builder.setCancelable(false);
builder.setPositiveButton("예", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
ActivityCompat.requestPermissions(mActivity,
new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION},
PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION);
}
});
builder.setNegativeButton("아니오", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
finish();
}
});
builder.create().show();
}
private void showDialogForPermissionSetting(String msg) {
AlertDialog.Builder builder = new AlertDialog.Builder(Main2Activity.this);
builder.setTitle("알림");
builder.setMessage(msg);
builder.setCancelable(true);
builder.setPositiveButton("예", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
askPermissionOnceAgain = true;
Intent myAppSettings = new Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS,
Uri.parse("package:" + mActivity.getPackageName()));
myAppSettings.addCategory(Intent.CATEGORY_DEFAULT);
myAppSettings.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
mActivity.startActivity(myAppSettings);
}
});
builder.setNegativeButton("아니오", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
finish();
}
});
builder.create().show();
}
//여기부터는 GPS 활성화를 위한 메소드들
private void showDialogForLocationServiceSetting() {
AlertDialog.Builder builder = new AlertDialog.Builder(Main2Activity.this);
builder.setTitle("위치 서비스 비활성화");
builder.setMessage("앱을 사용하기 위해서는 위치 서비스가 필요합니다.\n"
+ "위치 설정을 수정하실래요?");
builder.setCancelable(true);
builder.setPositiveButton("설정", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int id) {
Intent callGPSSettingIntent
= new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivityForResult(callGPSSettingIntent, GPS_ENABLE_REQUEST_CODE);
}
});
builder.setNegativeButton("취소", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
builder.create().show();
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
switch (requestCode) {
case GPS_ENABLE_REQUEST_CODE:
//사용자가 GPS 활성 시켰는지 검사
if (checkLocationServicesStatus()) {
if (checkLocationServicesStatus()) {
Log.d(TAG, "onActivityResult : 퍼미션 가지고 있음");
if ( mGoogleApiClient.isConnected() == false ) {
Log.d( TAG, "onActivityResult : mGoogleApiClient connect ");
mGoogleApiClient.connect();
}
return;
}
}
break;
}
}
}
和此MainActivity代码
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button bttest1 = (Button)findViewById(R.id.bttest1);
bttest1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(getApplicationContext(),Main2Activity.class);
startActivity(intent);
}
});
}
}
无法启动活动ComponentInfo {...}：java.lang.NullPointerException
此处发生错误。（Main2Activity）
mapFragment.getMapAsync(this);
该错误的原因是什么？ 请帮帮我。
答案 0 :(得分：1)
在Main2Activity onCreate中，您使用setContentView(R.layout.activity_main);
它似乎是来自MainActivity的布局，而不是Main2Activity。您应该在第二个活动中输入类似R.layout.activity_main2的内容。
然后输入您的代码
MapFragment mapFragment = (MapFragment) getFragmentManager()
.findFragmentById(R.id.map);
可能找不到ID为R.id.map的视图，因为该视图不是第一个MainActivity布局的一部分。