如何正确保护GoogleMap免于空?
它目前在 drawOnMap()
方法中表示mMap null,但在将其添加到 onMapReady()
方法时有效 .
我想知道因为如果我在 onMapReady()
内要求 drawOnMap()
,在我从我的意图中获取值之前可能会启动 Map 是不是真的?
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(startLatLng,10));
public class DetailActivity extends AppCompatActivity implements OnMapReadyCallback {
private GoogleMap mMap;
private String locationA;
private String locationB;
private ArrayList<LatLng> latLngList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
// Check if Google Maps have been activated, else starting it again.
if (mMap == null) {
SupportMapFragment smf = (SupportMapFragment) this.getSupportFragmentManager().findFragmentById(R.id.map);
smf.getMapAsync(this);
}
// Settings up the views
TextView mDistance = (TextView) findViewById(R.id.distanceDetail);
TextView mDuration = (TextView) findViewById(R.id.durationDetail);
TextView mLocationA = (TextView) findViewById(R.id.locationA);
TextView mLocationB = (TextView) findViewById(R.id.locationB);
// Getting the values
Intent i = getIntent();
locationA = i.getStringExtra("locA");
locationB = i.getStringExtra("locB");
String distance = i.getStringExtra("distance");
String duration = i.getStringExtra("duration");
// initiate the values.
mDistance.setText(distance);
mDuration.setText(duration);
mLocationA.setText(locationA);
mLocationB.setText(locationB);
drawOnMap();
}
public void drawOnMap(){
latLngList = getIntent().getParcelableArrayListExtra("points");
// Används för att rita ut marksen på kartan sedan, start och stop.
// Get the first and last postion to write out the marks on map
LatLng startLatLng = latLngList.get(0);
LatLng endLatLng = latLngList.get(latLngList.size() - 1);
// Zooms into the start position;
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(startLatLng, 10));
// Adding mark to start location
mMap.addMarker(new MarkerOptions()
.position(startLatLng)
.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_GREEN))
.title(locationA));
// Adding mark to end location
mMap.addMarker(new MarkerOptions()
.position(endLatLng)
.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED))
.title(locationB));
if (latLngList.size() > 0) {
// Draw the route on map
mMap.addPolyline(new PolylineOptions()
.addAll(latLngList)
.color(Color.argb(255, 55, 160, 255))
.width(20));
}
}
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
UiSettings mapSettings = mMap.getUiSettings();
mapSettings.setZoomControlsEnabled(true);
}
Catlog
java.lang.NullPointerException:尝试在android.app上的空对象引用上调用虚拟方法'void com.google.android.gms.maps.GoogleMap.moveCamera(com.google.android.gms.maps.CameraUpdate)' .ActivityThread.performLaunchActivity(ActivityThread.java:2416)位于android.app.A活动中的android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)android.app.ActivityThread $ H.handleMessage上的android.app.ActivityThread.-wrap11(ActivityThread.java) (ActivityThread.java:1344)android.app.Handler.dispatchMessage(Handler.java:102)位于android.app.ActivityThread.main的android.os.Looper.loop(Looper.java:148)(ActivityThread.java: 5417)位于com.android.internal.os.ZygoteInit.main的com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:726)的java.lang.reflect.Method.invoke(Native Method)( ZygoteInit.java:616)引起:java.lang.NullPointerException:尝试调用虚拟方法'void com.google.android.gms.maps.GoogleMap.moveCamera(com.google.android.gms.maps.Camera更新)'com.example.rasmusjosefsson.rjcar.DetailActivity.drawOnMap(DetailActivity.java:113)上的null对象引用,位于android.app的com.example.rasmusjosefsson.rjcar.DetailActivity.onCreate(DetailActivity.java:96) .Activity.performCreate(Activity.java:6237)位于android.app.A.运行中的android.app.Anstrumentation.callActivityOnCreate(Instrumentation.java:1107)android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369),android.app.ActivityThread.handleLaunchActivity( ActivityThread.java:2476)在android.app.Handler.dispatchMessage的android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1344)的android.app.ActivityThread.-wrap11(ActivityThread.java)处(Handler.java: 102)在android.app.Looper.loop(Looper.java:148)的android.app.ActivityThread.main(ActivityThread.java:5417),位于com.android的java.lang.reflect.Method.invoke(Native Method) .internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:726)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
2 回答
映射准备好后调用drawOnMap方法 .
您将在
onMapReady()
方法中获取谷歌 Map 对象,这就是为什么从这里调用drawOnMap()