从数据库android获取google map数据的问题

问题描述 投票：0回答：1

我正在开发使用Google Maps的应用。因此，我尝试使用此代码来显示来自数据库的google map标记。但是当我尝试它时，我面临如下问题：

我使用Mysql数据库和php文件存储纬度和经度。

任何人都知道解决方案吗？ 

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);

        mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        gMap = googleMap;

        // Mengarahkan ke alun-alun Demak
        center = new LatLng(-6.894796, 110.638413);
        cameraPosition = new CameraPosition.Builder().target(center).zoom(10).build();
        googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

        getMarkers();
    }

    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 strReq = 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();
            }
        });

        AppController.getInstance().addToRequestQueue(strReq, tag_json_obj);
    }

}

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..


E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.currentplacedetailsonmap, PID: 3285
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.currentplacedetailsonmap/com.example.currentplacedetailsonmap.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
        at android.app.ActivityThread.access$800(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        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)
     Caused by: java.lang.NullPointerException
        at com.example.currentplacedetailsonmap.MainActivity.onCreate(MainActivity.java:51)
        at android.app.Activity.performCreate(Activity.java:5231)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233) 
        at android.app.ActivityThread.access$800(ActivityThread.java:135) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        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) 
D/dalvikvm: GC_FOR_ALLOC freed 321K, 9% free 4107K/4484K, paused 7ms, total 7ms
E/dalvikvm: Could not find class 'dalvik.system.DelegateLastClassLoader', referenced from method com.google.android.gms.dynamite.DynamiteModule.a
android google-maps dictionary android-volley
1个回答
0
投票

NullPointerException错误发生在使用错误的片段管理器时，如果找不到片段，则返回null。您的片段使用SupportMapFragment，因此请使用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。

这是一个类似于您的代码的地图片段的简单示例，并且很成功-我已经发布了所有相关部分-因此请仔细阅读。除了不使用适当的片段管理器外，您可能还会遇到涉及权限和MapMan密钥（如AndroidManifest.xml中所列）的其他错误。

一旦到此为止，请将getMarkers()添加到onMapReady并继续进行。

AndroidManifest.xml

[[请注意地图片段和地图API密钥所需的权限。]

<?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" /> <!-- https://stackoverflow.com/a/52382711/2711811 -->
    <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: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（app）

dependencies {
    ...
    implementation 'com.google.android.gms:play-services-maps:17.0.0'
}

activity_main.xml

[与发布相同]

<?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 {


    @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;

        // 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：

enter image description here

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