我正在尝试在活动片段中设置com.google.android.gms.maps.SupportMapFragment。它在第三个片段上，但是当我尝试多种方法时，出现空指针异常。我认为解决方案位于代码内，可能位于position = 2的代码部分内？这是在地图片段显示在屏幕上时执行的代码。
我意识到这是一个空指针异常，但是解决此问题的要求是不同的，并且与普通程序不同，在普通程序中，我可以在开始时对其进行定义，并且在使用片段的情况下它可以正常工作，这会导致很多问题我
我能够将地图包含在xml中，当我访问放置在地图中的片段时，我可以看到地图并且可以与之交互，但是当我尝试以编程方式添加标记甚至初始化地图时崩溃。
我已经尝试过使用默认的地图活动中的代码来尝试地图，supportmapfragments和许多其他事情。
这是我的map_fragment.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_below="@+id/longText"
android:layout_marginBottom="50dp"
android:background="@color/White"
android:text="Map Screen"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="84dp"
android:textAlignment="center"
android:textAppearance="@style/TextAppearance.AppCompat.Display1" />
<fragment
class="com.google.android.gms.maps.SupportMapFragment"
android:id="@+id/map"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="140dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:layout_marginBottom="50dp"/>
</FrameLayout>
您可以看到该片段的ID为“地图”
这是我的参考活动
public class HomeActivity extends AppCompatActivity implements GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener, LocationListener, MyRecyclerViewAdapter.ItemClickListener, OnMapReadyCallback {
// SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
// .findFragmentById(R.id.map);
// mapFragment.getMapAsync(this);
private SessionHandler session;
private ProgressDialog pDialog;
GoogleApiClient mGoogleApiClient;
LocationManager mLocationManager;
TextView tv1;
TextView tv2;
Double globalLong;
Double globalLat;
private SwipeRefreshLayout mSwipeRefreshLayout;
private MyRecyclerViewAdapter adapter;
Location mLastLocation;
// private GoogleMap mMap;
//
// private static MapView mapView;
private static MapView mapFragment;
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);
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);
// SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
// .findFragmentById(R.id.map);
// mapFragment.getMapAsync(this);
TabLayout tabLayout = (TabLayout) findViewById(R.id.am_tab_layout);
// mSwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swipeRefreshLayout);
tabLayout.setupWithViewPager(viewPager);
//call method to load the data to the feed
loadLocations();
//set screen to view fragment 1 (centre)
viewPager.setCurrentItem(1);
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
if(position == 0)
{
}
}if(position == 1){
Button reload = (Button) findViewById(R.id.reload);
reload.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//when reload icon is pressed, reload data
loadLocations();
}
});
}if(position ==2){
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(HomeActivity.this);
Toast.makeText(HomeActivity.this, "Position 2", Toast.LENGTH_SHORT).show();
onMapReady(gmap);
}
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
private void loadLocations() {
//(code removed)
//load locations for fragment 1
}
@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();
}
@Override
protected void onStart() {
super.onStart();
}
@Override
protected void onStop() {
super.onStop();
}
@Override
public void onLocationChanged(Location location) {
double currentLatitude = location.getLatitude();
double currentLongitude = location.getLongitude();
globalLat = location.getLatitude();
globalLong = location.getLongitude();
Log.d("Location","Longitude = "+currentLongitude);
Log.d("Location","Latitude = "+currentLatitude);
if(tv1 != null)
tv1.setText(Double.toString(currentLatitude));
if(tv2 != null)
tv2.setText(Double.toString(currentLongitude));
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
//progress bar
private void displayLoader() {
pDialog = new ProgressDialog(HomeActivity.this);
pDialog.setMessage("Loading.. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
@Override
public void onItemClick(View view, int position) {
Toast.makeText(this, "This is item number " + adapter.getItem(position), Toast.LENGTH_SHORT).show();
}
@Override //saves instant state
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);
}
}
//life cycle
@Override
protected void onPause() {
super.onPause();
}
@Override
protected void onDestroy() {
super.onDestroy();
}
@Override
public void onLowMemory() {
super.onLowMemory();
}
@Override
public void onMapReady(GoogleMap map) {
//mMap = googleMap;
// Add a marker in Sydney and move the camera
// LatLng sydney = new LatLng(-34, 151);
// mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
// mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
//Toast.makeText(this, "some toast", Toast.LENGTH_SHORT).show();
//mMap.setMapStyle()
// gmap=map;
//
// gmap.addMarker(new MarkerOptions()
// .position(new LatLng(10, 10))
// .title("Hello world"));
//gmap.clear();
}
// void refreshItems() {
// // Load items
// loadLocations();
// // Load complete
// onItemsLoadComplete();
// }
//
// void onItemsLoadComplete() {
// // Update the adapter and notify data set changed
// // ...
//
// // Stop refresh animation
// mSwipeRefreshLayout.setRefreshing(false);
// }
}
我知道我的代码很乱，如果很难阅读，对不起。
我希望能够在地图上设置标记，但是每次尝试都将其崩溃。在运行mapFragment.getMapAsync(HomeActivity.this);部分中看到的(position=2)时，出现以下错误
2019-05-08 00:58:17.485 32151-32151/im.craig.locateio E/AndroidRuntime: FATAL EXCEPTION: main
Process: im.craig.locateio, PID: 32151
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.SupportMapFragment.getMapAsync(com.google.android.gms.maps.OnMapReadyCallback)' on a null object reference
at im.craig.locateio.HomeActivity$1.onPageSelected(HomeActivity.java:386)
at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1947)
at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:686)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:670)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:631)
at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:612)
at android.support.design.widget.TabLayout$ViewPagerOnTabSelectedListener.onTabSelected(TabLayout.java:2831)
at android.support.design.widget.TabLayout.dispatchTabSelected(TabLayout.java:1608)
at android.support.design.widget.TabLayout.selectTab(TabLayout.java:1601)
at android.support.design.widget.TabLayout.selectTab(TabLayout.java:1569)
at android.support.design.widget.TabLayout$Tab.select(TabLayout.java:1874)
at android.support.design.widget.TabLayout$TabView.performClick(TabLayout.java:2059)
at android.view.View$PerformClick.run(View.java:24770)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
2019-05-08 00:58:18.140 32151-32228/im.craig.locateio W/DynamiteModule: Local module descriptor class for com.google.android.gms.googlecertificates not found.
2019-05-08 00:58:18.150 32151-32228/im.craig.locateio I/DynamiteModule: Considering local module com.google.android.gms.googlecertificates:0 and remote module com.google.android.gms.googlecertificates:4
2019-05-08 00:58:18.150 32151-32228/im.craig.locateio I/DynamiteModule: Selected remote version of com.google.android.gms.googlecertificates, version >= 4
2019-05-08 00:58:18.160 32151-32228/im.craig.locateio W/zygote64: Unsupported class loader
2019-05-08 00:58:18.165 32151-32228/im.craig.locateio W/zygote64: Skipping duplicate class check due to unsupported classloader
但是，即使我尝试在它之前重新初始化，我似乎也会出现错误。
关于我的程序的另一个值得注意的事情可能是，当如上所示的if(position == 1){时，我正在那里创建一个on click监听器并在其中初始化内容，这是我需要做的才能使其正常运行。
您可能还会看到，我试图将以下代码放在没有运气的地方。
// SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
// .findFragmentById(R.id.map);
// mapFragment.getMapAsync(this);