android - 如何将 SQLite 数据库中的标记输出到 MapView 和 Google Map

Question

我已经设置了我的代码，所以当用户移动到 map fragment 时，它会显示一张 map ，其中包含数据库中的所有标记。我有两个虚拟标记，它们可以工作，但我数据库中的那些不显示。

我已确保 SQL 查询正确并尝试添加静态标记，但动态标记没有显示。

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.map,container,false);
    mapView = (MapView) rootView.findViewById(R.id.mapView);
    mapView.onCreate(savedInstanceState);
    mapView.getMapAsync(new OnMapReadyCallback() {
        @Override
        public void onMapReady(GoogleMap googleMap) {
            Log.i("DEBUG", "onMapReady");
            map = googleMap;
            LatLng sydney = new LatLng(-34, 151);
            LatLng paris = new LatLng(12,-40);
            map.addMarker(new 
            MarkerOptions().position(sydney).title("Marker in Sydney"));
            map.addMarker(new 
            MarkerOptions().position(paris).title("Marker in Ocean"));
              try {
                  String sql = "SELECT 
                         marker.markerLat,marker.markerLon,marker.markerDate 
                        FROM marker LEFT JOIN tripMarker ON" +
                         " marker.markerID = tripMarker.markerID LEFT 
                         JOIN userTrip ON userTrip.tripID = 
                         tripMarker.tripID " +
                       "WHERE userTrip.userID = '" + User.UserLoggedOn 
                         + "';";
                  Cursor cursor = db.rawQuery(sql, null);
                  if ( cursor.moveToFirst() ) {
                      while (cursor.moveToNext()) {
                          double lat = 
                       cursor.getDouble(cursor.getColumnIndex("markerLat"));
                          System.out.println(lat);
                          double lon = 
                       cursor.getDouble(cursor.getColumnIndex("markerLon"));
                          System.out.println(lon);
                          LatLng latLng = new LatLng(lat, lon);
                          MarkerOptions markerOptions = new 
                          MarkerOptions();
                          markerOptions.position(latLng);                        
                         map.addMarker(markerOptions.title(cursor.getString(
                          cursor.getColumnIndex("markerDate"))));
                      }
                  }
              }catch (Exception e){
                  e.printStackTrace();
              }
        }
    });
    return rootView;
    }

这是我的 fragment XML

<com.google.android.gms.maps.MapView
android:id="@+id/mapView"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
class="com.google.android.gms.maps.SupportMapFragment" />

Answer 1

您应该跳过第一行吗？它是唯一会返回的行吗？

也许日志记录无法按照评论工作的原因:-

for some reason, I have put logs in the if statement and in the catch, but I cant seem to find them. Does that mean they both dont trigger?

也许您应该尝试使用(删除 if (csr.moveToFirst()) 将跳过第一行):-

          MarkerOptions().position(paris).title("Marker in Ocean"));
          try {
              String sql = "SELECT 
                     marker.markerLat,marker.markerLon,marker.markerDate 
                    FROM marker LEFT JOIN tripMarker ON" +
                     " marker.markerID = tripMarker.markerID LEFT 
                     JOIN userTrip ON userTrip.tripID = 
                     tripMarker.tripID " +
                   "WHERE userTrip.userID = '" + User.UserLoggedOn 
                     + "';";
              Cursor cursor = db.rawQuery(sql, null);
              while (cursor.moveToNext()) {
                      double lat = 
                  cursor.getDouble(cursor.getColumnIndex("markerLat"));
                  System.out.println(lat);
                  double lon = 
                  cursor.getDouble(cursor.getColumnIndex("markerLon"));
                  System.out.println(lon);
                  LatLng latLng = new LatLng(lat, lon);
                  MarkerOptions markerOptions = new 
                      MarkerOptions();
                  markerOptions.position(latLng);                        
                  map.addMarker(markerOptions.title(cursor.getString(
                      cursor.getColumnIndex("markerDate"))));
              }
          }catch (Exception e){
              e.printStackTrace();
          }

我还会放弃将代码包装在 try/catch 子句中，您可能会隐藏问题。