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我正在嘗試使用加載程序來更新地圖上的標記。以下是我的代碼。問題在於即使我點擊刷新標記數據庫的應用程序上的刷新按鈕，標記也不會出現。這是一個適當的方式來實現這個裝載機？加載程序不更新片段內的地圖標記
package com.example.genexli.policev3;
import android.Manifest;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.ContextCompat;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.example.genexli.policev3.data.DataContract;
import com.google.android.gms.maps.CameraUpdate;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapView;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
/**
* A fragment for the map
*/
public class MapFragment extends Fragment implements OnMapReadyCallback,
LoaderManager.LoaderCallbacks<Cursor>{
MapView m;
GoogleMap map;
Cursor hotspots;
Cursor crimes;
Cursor police;
// three instance variable cursors: hotspots, crime and police.
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// save as an instance variable.
// init three loaders with different IDs. 0 = Hotspots, 1 = crime, 2 = police.
getLoaderManager().initLoader(0, null, this);
getLoaderManager().initLoader(1, null, this);
getLoaderManager().initLoader(2, null, this);
super.onActivityCreated(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// inflate and return the layout
View v = inflater.inflate(R.layout.fragment_map, container,
false);
// this creates the mapview.
m = (MapView) v.findViewById(R.id.mapView);
m.onCreate(savedInstanceState);
// in here it should load the markers using those instance variable cursors.
m.getMapAsync(this);
return v;
}
// Some required methods for MapView to function correctly.
@Override
public void onResume() {
m.onResume();
super.onResume();
}
@Override
public void onDestroy() {
super.onDestroy();
m.onDestroy();
}
@Override
public void onLowMemory() {
super.onLowMemory();
m.onLowMemory();
}
@Override
public void onMapReady (GoogleMap googleMap){
map = googleMap;
if (ContextCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
Log.v("Map", "location set");
map.setMyLocationEnabled(true);
map.getUiSettings().setMyLocationButtonEnabled(true);
} else {
requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);
}
CameraPosition target = CameraPosition.builder()
.target(new LatLng(36.1447034, -86.8032))
.zoom(13)
.build();
CameraUpdate cameraUpdate = CameraUpdateFactory.newCameraPosition(target);
map.moveCamera(cameraUpdate);
map.getUiSettings().setZoomControlsEnabled(true);
map.clear();
// map put hotspot markers
// map put crime markers
// map put police markers
if (hotspots != null) {
if(hotspots.moveToFirst())
// put in new marker.
do {
int idx_lat = hotspots.getColumnIndexOrThrow("latitude");
int idx_long = hotspots.getColumnIndexOrThrow("longitude");
Log.v("lat and long", hotspots.getDouble(idx_lat) + " " + hotspots.getDouble(idx_long));
LatLng ltlng = new LatLng(hotspots.getDouble(idx_lat), hotspots.getDouble(idx_long));
map.addMarker(new MarkerOptions().position(ltlng).title("Hotspot"));
} while (hotspots.moveToNext());
}
if (crimes != null) {
if(crimes.moveToFirst())
// put in new marker.
do {
int idx_lat = crimes.getColumnIndexOrThrow("latitude");
int idx_long = crimes.getColumnIndexOrThrow("longitude");
Log.v("lat and long", crimes.getDouble(idx_lat) + " " + crimes.getDouble(idx_long));
LatLng ltlng = new LatLng(crimes.getDouble(idx_lat), crimes.getDouble(idx_long));
map.addMarker(new MarkerOptions().position(ltlng).title("Crime"));
} while (crimes.moveToNext());
}
if (police != null) {
if(police.moveToFirst())
// put in new marker.
do {
int idx_lat = police.getColumnIndexOrThrow("latitude");
int idx_long = police.getColumnIndexOrThrow("longitude");
Log.v("lat and long", police.getDouble(idx_lat) + " " + police.getDouble(idx_long));
LatLng ltlng = new LatLng(police.getDouble(idx_lat), police.getDouble(idx_long));
map.addMarker(new MarkerOptions().position(ltlng).title("Police")
.icon(BitmapDescriptorFactory.fromResource(R.mipmap.ic_launcher)));
} while (police.moveToNext());
}
}
@Override
public void onStart() {
super.onStart();
// do I need to update all cursors when it is started?
}
@Override
public Loader<Cursor> onCreateLoader(int i, Bundle b) {
// switch here to assign loader to different cursor based off of the call.
switch(i) {
//0 = Hotspots, 1 = crime, 2 = police.
case 0: {
return new CursorLoader(getActivity(), DataContract.HotspotsEntry.CONTENT_URI,
null, null, null, null);
}
case 1: {
return new CursorLoader(getActivity(), DataContract.CrimesEntry.CONTENT_URI,
null, null, null, null);
}
case 2: {
return new CursorLoader(getActivity(), DataContract.PatrolsEntry.CONTENT_URI,
null, null, null, null);
}
}
return null;
}
// on loadfinished swaps loaders: use getId() to find the right cursor
public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) {
int id = cursorLoader.getId();
switch(id) {
case 0: {
hotspots = cursor;
break;
}
case 1: {
crimes = cursor;
}
case 2: {
police = cursor;
}
}
// reload the map?
}
//onloaderreset
@Override
public void onLoaderReset(Loader<Cursor> cursorLoader) {
hotspots = null;
crimes = null;
police = null;
}
}
我們真的需要檢查200行代碼？我相信你可以指出問題出在哪裏 – agustin