无法启动使用GPS检测android设备位置的活动实现LocationListener

我开发了一个简单的应用程序，可以检测android设备的位置，并在文本视图中显示其值

一旦应用程序开始抛出RuntimeException，它就会崩溃

下面是GPS.java

public class GPS extends Activity implements LocationListener {
    private TextView latituteField;
    private TextView longitudeField;
    private LocationManager locationManager;
    private String provider;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.gps);
        latituteField = (TextView) findViewById(R.id.TextView02);
        longitudeField = (TextView) findViewById(R.id.TextView04);

        LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
        boolean enabled = service
                .isProviderEnabled(LocationManager.GPS_PROVIDER);

        if (!enabled) {
            Intent intent = new Intent(
                    android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
            startActivity(intent);
        }

      Criteria criteria = new Criteria();
     provider = locationManager.getBestProvider(criteria,false);
    Location location = locationManager.getLastKnownLocation(provider);

        if (location != null) {
            Log.d("PROVIDER", "Provider " + provider + " has been selected.");

            onLocationChanged(location);
        } else {
            latituteField.setText("Location not available");
            longitudeField.setText("Location not available");
        }
    }

日志如下：

10-09 16:49:35.733:E/AndroidRuntime（1616）：致命异常：主 10-09 16:49:35.733:E/AndroidRuntime（1616）： java.lang.RuntimeException:无法启动活动 ComponentInfo{com.example.gps/com.example.gps.gps}： java.lang.NullPointerException 10-09 16:49:35.733： E/AndroidRuntime（1616）：在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:1956） 10-09 16:49:35.733:E/AndroidRuntime（1616）：在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:1981） 10-09 16:49:35.733:E/AndroidRuntime（1616）：在 android.app.ActivityThread.access$600（ActivityThread.java:123）10-09 16:49:35.733:E/AndroidRuntime（1616）：在 android.app.ActivityThread$H.handleMessage（ActivityThread.java:1147） 10-09 16:49:35.733:E/AndroidRuntime（1616）：在 android.os.Handler.dispatchMessage（Handler.java:99）10-09 16:49:35.733:E/AndroidRuntime（1616）：在 android.os.Looper.loop（Looper.java:137）10-09 16:49:35.733： E/AndroidRuntime（1616）：在 android.app.ActivityThread.main（ActivityThread.java:4424）10-09 16:49:35.733:E/AndroidRuntime（1616）：在 java.lang.reflect.Method.Invokenactive（本机方法）10-09 16:49:35.733:E/AndroidRuntime（1616）：在 java.lang.reflect.Method.invoke（Method.java:511）10-09 16:49:35.733: E/AndroidRuntime（1616）：在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run（ZygoteInit.java:784） 10-09 16:49:35.733:E/AndroidRuntime（1616）：在 com.android.internal.os.ZygoteInit.main（ZygoteInit.java:551）10-09 16:49:35.733:E/AndroidRuntime（1616）：在 dalvik.system.Nativestar.main（本地方法）10-09 16:49:35.733： E/AndroidRuntime（1616）：由以下原因引起：java.lang.NullPointerException 10-09 16:49:35.733:E/AndroidRuntime（1616）：在 com.example.gps.gps.onCreate（gps.java:44）10-09 16:49:35.733： E/AndroidRuntime（1616）：在 android.app.Activity.performCreate（Activity.java:4465）10-09 16:49:35.733:E/AndroidRuntime（1616）：在 android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1049） 10-09 16:49:35.733:E/AndroidRuntime（1616）：在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:1920） 10-09 16:49:35.733:E/AndroidRuntime（1616）：。。。还有11个

---

看起来问题出在显示位置设置屏幕时

使用以下代码启用/禁用GPS

公开无效turnGPSOn（） {

}

公共空间的转换 {

---

}我想你可能已经找到了解决办法。但我为将来可能有相同问题的人发布了此答案。您只声明了

locationManager

，但尚未初始化它。但是您后来声明了新的

LocationManager

调用了

service

。因此，您可以将服务作为

LocationManager

用于您的活动，也可以像这样初始化

LocationManager

public class GPS extends Activity implements LocationListener {
private TextView latituteField;
private TextView longitudeField;
private LocationManager locationManager;
private String provider;


@Override 
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.gps);
    latituteField = (TextView) findViewById(R.id.TextView02);
    longitudeField = (TextView) findViewById(R.id.TextView04);

    locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);//now you have initialised locationManager, and is available for use.
    LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);//Declared and initialised new LocationManager service but only accessible inside onCreate method. 
    boolean enabled = locationManager
            .isProviderEnabled(LocationManager.GPS_PROVIDER);

    if (!enabled) {
        Intent intent = new Intent(
                android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
        startActivity(intent);
    } 

  Criteria criteria = new Criteria();
 provider = locationManager.getBestProvider(criteria,false);
Location location = locationManager.getLastKnownLocation(provider);

    if (location != null) { 
        Log.d("PROVIDER", "Provider " + provider + " has been selected.");

        onLocationChanged(location); 
    } else { 
        latituteField.setText("Location not available");
        longitudeField.setText("Location not available");
    } 
} `

---

现在将不会出现任何空指针异常。

您可以在此处附加崩溃日志吗？检查清单文件中的所有权限，并请附加日志。您已调用MainActivity类，但您想调用gps类。在AndroidMenifestFile中用GPS替换MainActivity我编辑帖子很抱歉格式不好，但我不知道如何以良好的格式发布。是的，我知道这一行会导致应用程序崩溃，但我不知道为什么。对不起，但问题不在这一部分。这一行的问题provider=locationManager.getBestProvider（criteria，false）；它抛出空指针异常locationManager为空。您尚未初始化它。您可以使用下面的代码locationManager=（locationManager）getSystemService（Context.LOCATION\u SERVICE）初始化它；

String provider = Settings.Secure.getString(ctx.getContentResolver(), Settings.Secure.LOCATION_PROVIDERS_ALLOWED);
if(provider.contains("gps")){ //if gps is enabled
    final Intent poke = new Intent();
    poke.setClassName("com.android.settings", "com.android.settings.widget.SettingsAppWidgetProvider");
    poke.addCategory(Intent.CATEGORY_ALTERNATIVE);
    poke.setData(Uri.parse("3")); 
    this.ctx.sendBroadcast(poke);
}

public class GPS extends Activity implements LocationListener {
private TextView latituteField;
private TextView longitudeField;
private LocationManager locationManager;
private String provider;


@Override 
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.gps);
    latituteField = (TextView) findViewById(R.id.TextView02);
    longitudeField = (TextView) findViewById(R.id.TextView04);

    locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);//now you have initialised locationManager, and is available for use.
    LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);//Declared and initialised new LocationManager service but only accessible inside onCreate method. 
    boolean enabled = locationManager
            .isProviderEnabled(LocationManager.GPS_PROVIDER);

    if (!enabled) {
        Intent intent = new Intent(
                android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
        startActivity(intent);
    } 

  Criteria criteria = new Criteria();
 provider = locationManager.getBestProvider(criteria,false);
Location location = locationManager.getLastKnownLocation(provider);

    if (location != null) { 
        Log.d("PROVIDER", "Provider " + provider + " has been selected.");

        onLocationChanged(location); 
    } else { 
        latituteField.setText("Location not available");
        longitudeField.setText("Location not available");
    } 
} `