从数据库 android 获取 google 地图数据时出现问题
Problem with Fetch google map data from the database android
我正在开发一个使用 Google Maps.So 的应用程序 我尝试使用此代码显示数据库中的 google 地图标记。但是当我尝试它时，我遇到了如下问题：
我使用Mysql数据库和php文件来存储纬度和经度。
有人知道解决办法吗？
public class MainActivity extends FragmentActivity implements OnMapReadyCallback {
MapFragment mapFragment;
GoogleMap gMap;
MarkerOptions markerOptions = new MarkerOptions();
CameraPosition cameraPosition;
LatLng center, latLng;
String title;
public static final String ID = "id";
public static final String TITLE = "nama";
public static final String LAT = "lat";
public static final String LNG = "lng";
private String url = "http://wisatademak.dedykuncoro.com/Main/json_wisata";
String tag_json_obj = "json_obj_req";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
@Override
public void onMapReady(GoogleMap map) {
GoogleMap gMap = map;
getMarkers();
// Mengarahkan ke alun-alun Demak
LatLng center = new LatLng(-6.894796, 110.638413);
CameraPosition cameraPosition = new CameraPosition.Builder().target(center).zoom(10).build();
gMap.animateCamera( CameraUpdateFactory.newCameraPosition (cameraPosition));
}
private void addMarker(LatLng latlng, final String title) {
markerOptions.position(latlng);
markerOptions.title(title);
gMap.addMarker(markerOptions);
gMap.setOnInfoWindowClickListener(new GoogleMap.OnInfoWindowClickListener() {
@Override
public void onInfoWindowClick(Marker marker) {
Toast.makeText(getApplicationContext(), marker.getTitle(), Toast.LENGTH_SHORT).show();
}
});
}
// Fungsi get JSON marker
private void getMarkers() {
StringRequest stringRequest = new StringRequest(Request.Method.POST, url, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.e("Response: ", response.toString());
try {
JSONObject jObj = new JSONObject(response);
String getObject = jObj.getString("wisata");
JSONArray jsonArray = new JSONArray(getObject);
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject = jsonArray.getJSONObject(i);
title = jsonObject.getString(TITLE);
latLng = new LatLng(Double.parseDouble(jsonObject.getString(LAT)), Double.parseDouble(jsonObject.getString(LNG)));
// Menambah data marker untuk di tampilkan ke google map
addMarker(latLng, title);
}
} catch (JSONException e) {
// JSON error
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("Error: ", error.getMessage());
Toast.makeText(MainActivity.this, error.getMessage(), Toast.LENGTH_LONG).show();
}
});
RequestQueue requestQueue= Volley.newRequestQueue(getApplicationContext());
requestQueue.add(stringRequest);
// AppController.getInstance().addToRequestQueue(strReq, tag_json_obj);
}
}
清单
<uses-permission android:name="android.permission.INTERNET" /> <!-- -->
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="@string/google_maps_key" />
implementation 'com.google.android.gms:play-services:6.5.87'
implementation 'com.android.volley:volley:1.1.1'
这是我的 XML
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
public class AppController extends Application {
public static final String TAG = AppController.class.getSimpleName();
private RequestQueue mRequestQueue;
private static AppController mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized AppController getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
req.setRetryPolicy(new DefaultRetryPolicy(0, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
req.setRetryPolicy(new DefaultRetryPolicy(0, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
mRequestQueue.cancelAll(tag);
}
}
}
这是 logcat..
的消息
04-12 09:08:06.101 10319-10319/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 10319
java.lang.NullPointerException
at com.example.myapplication.MainActivity.getMarkers(MainActivity.java:121)
at com.example.myapplication.MainActivity.onMapReady(MainActivity.java:60)
at com.google.android.gms.maps.SupportMapFragment$a.a(Unknown Source)
at com.google.android.gms.maps.internal.m$a.onTransact(Unknown Source)
at android.os.Binder.transact(Binder.java:361)
at hr.b(:com.google.android.gms.dynamite_mapsdynamite@18382015@18.3.82 (000700-260264002):14)
at com.google.android.gms.maps.internal.bc.a(:com.google.android.gms.dynamite_mapsdynamite@18382015@18.3.82 (000700-260264002):4)
at com.google.maps.api.android.lib6.impl.bl.run(:com.google.android.gms.dynamite_mapsdynamite@18382015@18.3.82 (000700-260264002):4)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
04-12 09:08:08.057 10319-10370/com.example.myapplication E/dalvikvm: Could not find class 'dalvik.system.DelegateLastClassLoader', referenced from method com.google.android.gms.dynamite.DynamiteModule.a
然后我替换了这一行
AppController.getInstance().addToRequestQueue(strReq, tag_json_obj);
被这个取代
RequestQueue requestQueue= Volley.newRequestQueue(getApplicationContext());
requestQueue.add(stringRequest);
替换上面的行后出现以下错误
04-13 02:18:02.586 2368-2368/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 2368
java.lang.NullPointerException
at com.example.myapplication.MainActivity.addMarker(MainActivity.java:71)
at com.example.myapplication.MainActivity.access[=20=]0(MainActivity.java:30)
at com.example.myapplication.MainActivity.onResponse(MainActivity.java:102)
at com.example.myapplication.MainActivity.onResponse(MainActivity.java:85)
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:82)
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:29)
at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:102)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
当使用不正确的片段管理器时会发生 NullPointerException 错误，如果找不到片段，returns null。您的片段使用 SupportMapFragment 因此使用 SupportFragmentManager 如下例所示。
您可能还有其他错误 - 取决于您如何设置 AndroidManifest.xml，如下所示。
这是一个与您的代码相似且成功的地图片段的简单示例 - 我已经 post 编辑了所有相关部分 - 所以请仔细阅读。除了没有使用正确的片段管理器之外，您可能会遇到其他错误，涉及 AndroidManifest.xml.
中列出的权限和映射 API 键
一旦你做到这一点，然后将你的 getMarkers() 添加到 onMapReady 并继续前进。
AndroidManifest.xml
[注意地图片段和地图 API 键所需的权限。]
[同时将 .AppController class 添加为应用程序 class 否则它不会自动实例化并且您的 getInstance 将 return 为空。]
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="<<your package>>">
<uses-permission android:name="android.permission.INTERNET" /> <!-- -->
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:name=".AppController"
android:theme="@style/AppTheme">
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="@string/google_maps_key" />
<activity android:name=".MainActivity">
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
build.gradle（应用程序）
dependencies {
...
implementation 'com.google.android.gms:play-services-maps:17.0.0'
}
activity_main.xml
[等同于post]
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
MainActivity.java
public class MainActivity extends FragmentActivity implements OnMapReadyCallback {
GoogleMap gMap;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
@Override
public void onMapReady(GoogleMap map) {
gMap = map;
// Mengarahkan ke alun-alun Demak
LatLng center = new LatLng(-6.894796, 110.638413);
CameraPosition cameraPosition = new CameraPosition.Builder().target(center).zoom(10).build();
gMap.animateCamera( CameraUpdateFactory.newCameraPosition (cameraPosition));
}
}
并显示：
我正在开发一个使用 Google Maps.So 的应用程序 我尝试使用此代码显示数据库中的 google 地图标记。但是当我尝试它时，我遇到了如下问题：
我使用Mysql数据库和php文件来存储纬度和经度。
有人知道解决办法吗？
public class MainActivity extends FragmentActivity implements OnMapReadyCallback {
MapFragment mapFragment;
GoogleMap gMap;
MarkerOptions markerOptions = new MarkerOptions();
CameraPosition cameraPosition;
LatLng center, latLng;
String title;
public static final String ID = "id";
public static final String TITLE = "nama";
public static final String LAT = "lat";
public static final String LNG = "lng";
private String url = "http://wisatademak.dedykuncoro.com/Main/json_wisata";
String tag_json_obj = "json_obj_req";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
@Override
public void onMapReady(GoogleMap map) {
GoogleMap gMap = map;
getMarkers();
// Mengarahkan ke alun-alun Demak
LatLng center = new LatLng(-6.894796, 110.638413);
CameraPosition cameraPosition = new CameraPosition.Builder().target(center).zoom(10).build();
gMap.animateCamera( CameraUpdateFactory.newCameraPosition (cameraPosition));
}
private void addMarker(LatLng latlng, final String title) {
markerOptions.position(latlng);
markerOptions.title(title);
gMap.addMarker(markerOptions);
gMap.setOnInfoWindowClickListener(new GoogleMap.OnInfoWindowClickListener() {
@Override
public void onInfoWindowClick(Marker marker) {
Toast.makeText(getApplicationContext(), marker.getTitle(), Toast.LENGTH_SHORT).show();
}
});
}
// Fungsi get JSON marker
private void getMarkers() {
StringRequest stringRequest = new StringRequest(Request.Method.POST, url, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.e("Response: ", response.toString());
try {
JSONObject jObj = new JSONObject(response);
String getObject = jObj.getString("wisata");
JSONArray jsonArray = new JSONArray(getObject);
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject = jsonArray.getJSONObject(i);
title = jsonObject.getString(TITLE);
latLng = new LatLng(Double.parseDouble(jsonObject.getString(LAT)), Double.parseDouble(jsonObject.getString(LNG)));
// Menambah data marker untuk di tampilkan ke google map
addMarker(latLng, title);
}
} catch (JSONException e) {
// JSON error
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("Error: ", error.getMessage());
Toast.makeText(MainActivity.this, error.getMessage(), Toast.LENGTH_LONG).show();
}
});
RequestQueue requestQueue= Volley.newRequestQueue(getApplicationContext());
requestQueue.add(stringRequest);
// AppController.getInstance().addToRequestQueue(strReq, tag_json_obj);
}
}
清单
<uses-permission android:name="android.permission.INTERNET" /> <!-- -->
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="@string/google_maps_key" />
implementation 'com.google.android.gms:play-services:6.5.87'
implementation 'com.android.volley:volley:1.1.1'
这是我的 XML
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
public class AppController extends Application {
public static final String TAG = AppController.class.getSimpleName();
private RequestQueue mRequestQueue;
private static AppController mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized AppController getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
req.setRetryPolicy(new DefaultRetryPolicy(0, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
req.setRetryPolicy(new DefaultRetryPolicy(0, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
mRequestQueue.cancelAll(tag);
}
}
}
这是 logcat..
的消息
04-12 09:08:06.101 10319-10319/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 10319
java.lang.NullPointerException
at com.example.myapplication.MainActivity.getMarkers(MainActivity.java:121)
at com.example.myapplication.MainActivity.onMapReady(MainActivity.java:60)
at com.google.android.gms.maps.SupportMapFragment$a.a(Unknown Source)
at com.google.android.gms.maps.internal.m$a.onTransact(Unknown Source)
at android.os.Binder.transact(Binder.java:361)
at hr.b(:com.google.android.gms.dynamite_mapsdynamite@18382015@18.3.82 (000700-260264002):14)
at com.google.android.gms.maps.internal.bc.a(:com.google.android.gms.dynamite_mapsdynamite@18382015@18.3.82 (000700-260264002):4)
at com.google.maps.api.android.lib6.impl.bl.run(:com.google.android.gms.dynamite_mapsdynamite@18382015@18.3.82 (000700-260264002):4)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
04-12 09:08:08.057 10319-10370/com.example.myapplication E/dalvikvm: Could not find class 'dalvik.system.DelegateLastClassLoader', referenced from method com.google.android.gms.dynamite.DynamiteModule.a
然后我替换了这一行
AppController.getInstance().addToRequestQueue(strReq, tag_json_obj);
被这个取代
RequestQueue requestQueue= Volley.newRequestQueue(getApplicationContext());
requestQueue.add(stringRequest);
替换上面的行后出现以下错误
04-13 02:18:02.586 2368-2368/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 2368
java.lang.NullPointerException
at com.example.myapplication.MainActivity.addMarker(MainActivity.java:71)
at com.example.myapplication.MainActivity.access[=20=]0(MainActivity.java:30)
at com.example.myapplication.MainActivity.onResponse(MainActivity.java:102)
at com.example.myapplication.MainActivity.onResponse(MainActivity.java:85)
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:82)
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:29)
at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:102)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
当使用不正确的片段管理器时会发生 NullPointerException 错误，如果找不到片段，returns null。您的片段使用 SupportMapFragment 因此使用 SupportFragmentManager 如下例所示。
您可能还有其他错误 - 取决于您如何设置 AndroidManifest.xml，如下所示。
这是一个与您的代码相似且成功的地图片段的简单示例 - 我已经 post 编辑了所有相关部分 - 所以请仔细阅读。除了没有使用正确的片段管理器之外，您可能会遇到其他错误，涉及 AndroidManifest.xml.
中列出的权限和映射 API 键一旦你做到这一点，然后将你的 getMarkers() 添加到 onMapReady 并继续前进。
AndroidManifest.xml
[注意地图片段和地图 API 键所需的权限。]
[同时将 .AppController class 添加为应用程序 class 否则它不会自动实例化并且您的 getInstance 将 return 为空。]
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="<<your package>>">
<uses-permission android:name="android.permission.INTERNET" /> <!-- -->
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:name=".AppController"
android:theme="@style/AppTheme">
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="@string/google_maps_key" />
<activity android:name=".MainActivity">
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
build.gradle（应用程序）
dependencies {
...
implementation 'com.google.android.gms:play-services-maps:17.0.0'
}
activity_main.xml
[等同于post]
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
MainActivity.java
public class MainActivity extends FragmentActivity implements OnMapReadyCallback {
GoogleMap gMap;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
@Override
public void onMapReady(GoogleMap map) {
gMap = map;
// Mengarahkan ke alun-alun Demak
LatLng center = new LatLng(-6.894796, 110.638413);
CameraPosition cameraPosition = new CameraPosition.Builder().target(center).zoom(10).build();
gMap.animateCamera( CameraUpdateFactory.newCameraPosition (cameraPosition));
}
}
并显示：