Question

我对Android编程很新，并一直在寻找解决这个问题的一些指示，但我似乎无法解决确切的问题。

我想我只需要一些指针，为什么以及它抛出NullPointerException的位置，以便我将来可以自己跟踪它。

相关代码的一些部分：

   private static final long TWO_MINUTES = 1000 * 60 * 2;
    private static final long TEN_SECONDS = 10000;
    private static final float TEN_METERS = 10;
    public static final String LOG_TAG = "Locally";
    private static LocationManager locMan;
    Button StopButton;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Toast.makeText(getApplicationContext(), "Attempting to start service",
                Toast.LENGTH_SHORT);

        startService(new Intent(LocallyActivity.this, LocallyService.class));

        StopButton = (Button) findViewById(R.id.button1);

        LocationManager locMan = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        double lat = 0;
        double longi = 0;
        TextView t = (TextView) findViewById(R.id.textView1);
        Criteria crit = new Criteria();
        String strLoc = locMan.getBestProvider(crit, true);
        Location lastKnown = locMan.getLastKnownLocation(strLoc);
        if (lastKnown != null) {
            lat = lastKnown.getLatitude();
            longi = lastKnown.getLongitude();
            long tsLong = System.currentTimeMillis() / 1000;
            long lastTime = lastKnown.getTime();
            long difference = tsLong - lastTime;

            Time time = new Time();
            time.set(Long.valueOf(lastTime));
            t.setText("" + lat + ", " + longi + " (" + strLoc + ", time: "
                    + time.hour + " " + time.minute + ")");

            Object networkLocation = requestUpdatesFromProvider(strLoc, 32);
        } else {
            t.setText("No last location from " + strLoc);
        }
    }

    private Location requestUpdatesFromProvider(final String provider,
            final int errorResId) {
        Location location = null;
        Log.v(LOG_TAG, provider);
        if (locMan.isProviderEnabled(provider)) {
            locMan.requestLocationUpdates(provider, TEN_SECONDS, TEN_METERS,
                    listener);
            location = locMan.getLastKnownLocation(provider);
        } else {
            Toast.makeText(this, errorResId, Toast.LENGTH_LONG).show();
        }
        return location;

    }

错误跟踪：

07-30 12:41:12.644: E/AndroidRuntime(20697): FATAL EXCEPTION: main
07-30 12:41:12.644: E/AndroidRuntime(20697): java.lang.RuntimeException: Unable to start         activity ComponentInfo{com.somnu.locally/com.somnu.locally.LocallyActivity}:     java.lang.NullPointerException
07-30 12:41:12.644: E/AndroidRuntime(20697):    at     android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.app.ActivityThread.access$600(ActivityThread.java:123)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.os.Looper.loop(Looper.java:137)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.app.ActivityThread.main(ActivityThread.java:4424)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at java.lang.reflect.Method.invokeNative(Native Method)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at java.lang.reflect.Method.invoke(Method.java:511)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at dalvik.system.NativeStart.main(Native Method)
07-30 12:41:12.644: E/AndroidRuntime(20697): Caused by: java.lang.NullPointerException
07-30 12:41:12.644: E/AndroidRuntime(20697):    at com.somnu.locally.LocallyActivity.requestUpdatesFromProvider(LocallyActivity.java:67)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at com.somnu.locally.LocallyActivity.onCreate(LocallyActivity.java:57)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.app.Activity.performCreate(Activity.java:4465)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
07-30 12:41:12.644: E/AndroidRuntime(20697):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
07-30 12:41:12.644: E/AndroidRuntime(20697):    ... 11 more

第67行是：

if (locMan.isProviderEnabled(provider)) {

Answer 1

我认为locMan is null so NPE...

使用

locMan = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

而不是

LocationManager locMan = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

在onCreate中出现NullPointerException，似乎无法在调试后找到原因

1 个答案: