我正在尝试将mapView放入片段中。但是onStart出现了问题，但是当我从onStart方法中删除mapView.onStart();时，地图在30秒后开始缓慢加载了吗？
尝试调用虚拟方法'void com.google.android.gms.maps.MapView.onStart（）”上的空对象 参考 在HomeActivity.onStart（HomeActivity.java:501）
（在这种情况下，第501行是“ mapView.onStart();”）
我尝试了不同的教程和重新格式化。我也尝试过使用其他Google API服务。我认为问题出在我使用的是碎片视图。
HomeActivity.java
public class HomeActivity extends AppCompatActivity implements GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener, LocationListener, MyRecyclerViewAdapter.ItemClickListener, OnMapReadyCallback {
private MapView mapView;
private GoogleMap gmap;
private static final String MAP_VIEW_BUNDLE_KEY = "MapViewBundleKey";
@Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
session = new SessionHandler(getApplicationContext());
final User user = session.getUserDetails();
final View background = findViewById(R.id.home_background_view);
final ViewPager viewPager = (ViewPager) findViewById(R.id.home_view_pager);
MainPagerAdapter adapter = new MainPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.am_tab_layout);
tabLayout.setupWithViewPager(viewPager);
loadLocations();
viewPager.setCurrentItem(1);
@Override
public void onPageSelected(int position) {
if(position == 0)
{
//code for first screen
}if(position == 2){
//code for when screen is on the Map View
Bundle mapViewBundle = null;
if (savedInstanceState != null) {
mapViewBundle = savedInstanceState.getBundle(MAP_VIEW_BUNDLE_KEY);
}
mapView = findViewById(R.id.mapView);
mapView.onCreate(mapViewBundle);
mapView.getMapAsync(HomeActivity.this);
}
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
@Override
public void onConnected(@Nullable Bundle bundle) {
}
@Override
public void onConnectionSuspended(int i) {
}
@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
}
@Override
protected void onResume() {
super.onResume();
mapView.onResume();
}
@Override
protected void onStart() {
super.onStart();
mapView.onStart();
}
@Override
protected void onStop() {
super.onStop();
mapView.onStop();
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Bundle mapViewBundle = outState.getBundle(MAP_VIEW_BUNDLE_KEY);
if (mapViewBundle == null) {
mapViewBundle = new Bundle();
outState.putBundle(MAP_VIEW_BUNDLE_KEY, mapViewBundle);
}
mapView.onSaveInstanceState(mapViewBundle);
}
@Override
protected void onPause() {
mapView.onPause();
super.onPause();
}
@Override
protected void onDestroy() {
mapView.onDestroy();
super.onDestroy();
}
@Override
public void onLowMemory() {
super.onLowMemory();
mapView.onLowMemory();
}
@Override
public void onMapReady(GoogleMap googleMap) {
gmap = googleMap;
//gmap.setMinZoomPreference(12);
LatLng ny = new LatLng(40.7143528, -74.0059731);
gmap.moveCamera(CameraUpdateFactory.newLatLng(ny));
}
}
fragment_map.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
tools:background="@color/CafeSeaBlue"
android:layout_height="match_parent"
android:layout_width="match_parent"
xmlns:tools="http://schemas.android.com/tools">
<View
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="80dp"
android:background="@drawable/card_background" />
<android.support.v7.widget.AppCompatTextView
android:id="@+id/latText1"
android:layout_width="match_parent"
android:layout_height="32dp"
android:layout_below="@+id/longText"
android:layout_marginTop="100dp"
android:layout_marginBottom="50dp"
android:background="@color/White"
android:text="Map Screen"
android:textAlignment="center"/>
<com.google.android.gms.maps.MapView
android:id="@+id/mapView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="150dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp" />
</FrameLayout>
Logcat
2019-05-01 14:15:33.397 20032-20032/im.craig.locateio E/AndroidRuntime: FATAL EXCEPTION: main
Process: im.craig.locateio, PID: 20032
java.lang.RuntimeException: Unable to start activity ComponentInfo{im.craig.locateio/im.craig.locateio.HomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.MapView.onStart()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.MapView.onStart()' on a null object reference
at im.craig.locateio.HomeActivity.onStart(HomeActivity.java:501)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1334)
at android.app.Activity.performStart(Activity.java:7029)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2741)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
答案 0 :(得分：0)
尝试使用Oncreate方法而不是onPageSelected方法初始化MapView。将其从onPageSelected方法中删除，并在OnCreate方法中进行。
mapView = findViewById(R.id.mapView);
此行下面会更好
viewPager.setCurrentItem(1);
所以看起来像这样。
viewPager.setCurrentItem(1);
mapView = findViewById(R.id.mapView);
答案 1 :(得分：-1)
您需要在Fragment＃OnDestroyView而不是Fragment＃onDestroy中调用onDestroy。掌握正确的生命周期将解决您的问题。