对此有新意见，但我看不出任何问题。设置中有一个复选框用于启动Async任务，因此onCreate中的if语句。我只是在执行任务的行上得到Java null错误。
代码
ProgressDialog progressDialog;
double longitude, latitude;
Location location;
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute
protected LocationManager locationManager;
GPSLocation task = new GPSLocation();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_confirm_screen);
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
Boolean locationCheck = sp.getBoolean("LOCATION", false);
if(locationCheck){
task.execute();
}
else
{
sendEmail();
playSound();
}
}
public double getLatitude()
{
if (location != null)
{
latitude = location.getLatitude();
}
return latitude;
}
public double getLongitude()
{
if (location != null)
{
longitude = location.getLongitude();
}
return longitude;
}
public class GPSLocation extends AsyncTask<Void, Void, Void> implements LocationListener
{
boolean running =true;
@Override
protected void onPreExecute()
{
super.onPreExecute();
progressDialog = new ProgressDialog(ConfirmScreen.this);
progressDialog.setOnCancelListener(new DialogInterface.OnCancelListener(){
public void onCancel(DialogInterface dialog) {
//getgps.cancel(true);
}
});
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("GPS Enabled", "GPS Enabled");
if (locationManager != null) {
location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
progressDialog.setCancelable(true);
progressDialog.setMessage("Getting GPS Location...");
progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
progressDialog.setProgress(1);
progressDialog.show();
}
}
}
@Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
// Things to be done while execution of long running operation is in progress. For example updating ProgessDialog
}
@Override
protected void onPostExecute(Void result)
{
progressDialog.cancel();
sendEmail("GPS: ", Double.toString(longitude).trim(), Double.toString(latitude).trim());
playSound();
}
@Override
protected Void doInBackground(Void... params) {
boolean isDataSubmitted = false;
while(!isDataSubmitted)
{
if(longitude !=0 && latitude!=0)
{
sendEmail(); //Send Email without co-ords
playSound();
isDataSubmitted = true;
}
}
return null;
}
@Override
public void onLocationChanged(Location location) {
// TODO Auto-generated method stub
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onStatusChanged(String provider, int status,
Bundle extras) {
// TODO Auto-generated method stub
}
}
public void backHome(View view)
{
Intent intent = new Intent (this, MainScreen.class);
startActivity(intent);
}
// Method to start playing and looping a sound.
public void playSound()
{
MediaPlayer clickSound = MediaPlayer.create(this, R.raw.warning);
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
Boolean soundCheck = sp.getBoolean("SOUND", false);
if (soundCheck)
{
clickSound.start();
}
}// method end
public void sendEmail()
{
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
String nameValue = sp.getString("NAME", "failed to get name");
String emailValue = sp.getString("EMAIL", "failed to get email");
Intent i = new Intent(Intent.ACTION_SEND);
i.setType("message/rfc822");
i.putExtra(Intent.EXTRA_EMAIL, new String[]{emailValue});
i.putExtra(Intent.EXTRA_SUBJECT, "Email sent from DON'T PANIC - A Chris O'Brien Project");
i.putExtra(Intent.EXTRA_TEXT, "Hi there\n" + nameValue + " is in mortal danger. They didn't include co-ords as they assume you know where they are..\nKind Regards\nDon't Panic! \n\n\n");
try
{ startActivity(Intent.createChooser(i, "Send mail...."));
}
catch (android.content.ActivityNotFoundException ex){
Toast.makeText(ConfirmScreen.this, "There are no email clients installed or set up", Toast.LENGTH_SHORT).show();
}
}
public void sendEmail(String a, String b, String c)
{
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
String nameValue = sp.getString("NAME", "failed to get name");
String emailValue = sp.getString("EMAIL", "failed to get email");
Intent i = new Intent(Intent.ACTION_SEND);
i.setType("message/rfc822");
i.putExtra(Intent.EXTRA_EMAIL, new String[]{emailValue});
i.putExtra(Intent.EXTRA_SUBJECT, "Email sent from DON'T PANIC - A Chris O'Brien Project");
i.putExtra(Intent.EXTRA_TEXT, "Hi there\n" + nameValue + " is in mortal danger. Please see the co-ords attached and run to their rescue!" +
" If you don't see any co-ords, they didn't check the box and assume you know where they are.\nKind Regards\nDon't Panic! \n\n\n" +
a + b + c);
try
{ startActivity(Intent.createChooser(i, "Send mail...."));
}
catch (android.content.ActivityNotFoundException ex){
Toast.makeText(ConfirmScreen.this, "There are no email clients installed or set up", Toast.LENGTH_SHORT).show();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_confirm_screen, menu);
return true;
}
}
调试信息
10-03 08:38:16.890: D/dalvikvm(27516): Late-enabling CheckJNI
10-03 08:38:16.990: I/dalvikvm(27516): Turning on JNI app bug workarounds for target SDK version 11...
10-03 08:38:17.030: E/Trace(27516): error opening trace file: No such file or directory (2)
10-03 08:38:17.600: D/dalvikvm(27516): GC_FOR_ALLOC freed 58K, 9% free 12206K/13315K, paused 105ms, total 111ms
10-03 08:38:17.610: I/dalvikvm-heap(27516): Grow heap (frag case) to 13.616MB for 784248-byte allocation
10-03 08:38:17.755: D/dalvikvm(27516): GC_CONCURRENT freed 1K, 8% free 12971K/14087K, paused 35ms+9ms, total 147ms
10-03 08:38:17.940: D/dalvikvm(27516): GC_FOR_ALLOC freed 0K, 8% free 12971K/14087K, paused 32ms, total 32ms
10-03 08:38:17.985: I/dalvikvm-heap(27516): Grow heap (frag case) to 16.606MB for 3136944-byte allocation
10-03 08:38:18.025: D/dalvikvm(27516): GC_CONCURRENT freed 0K, 7% free 16034K/17159K, paused 24ms+1ms, total 40ms
10-03 08:38:18.025: D/dalvikvm(27516): WAIT_FOR_CONCURRENT_GC blocked 4ms
10-03 08:39:44.110: E/SpannableStringBuilder(27516): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
10-03 08:39:44.110: E/SpannableStringBuilder(27516): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
10-03 08:39:45.145: E/SpannableStringBuilder(27516): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
10-03 08:39:45.145: E/SpannableStringBuilder(27516): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
10-03 08:39:45.910: D/dalvikvm(27516): GC_FOR_ALLOC freed 815K, 11% free 15718K/17543K, paused 9ms, total 9ms
10-03 08:39:45.910: I/dalvikvm-heap(27516): Grow heap (frag case) to 19.016MB for 2850872-byte allocation
10-03 08:39:45.925: D/dalvikvm(27516): GC_CONCURRENT freed 10K, 10% free 18492K/20359K, paused 1ms+1ms, total 12ms
10-03 08:39:45.955: D/dalvikvm(27516): GC_FOR_ALLOC freed 0K, 10% free 18492K/20359K, paused 9ms, total 9ms
10-03 08:39:45.970: I/dalvikvm-heap(27516): Grow heap (frag case) to 29.882MB for 11403440-byte allocation
10-03 08:39:45.990: D/dalvikvm(27516): GC_CONCURRENT freed 0K, 7% free 29628K/31559K, paused 11ms+2ms, total 22ms
10-03 08:39:46.025: D/AndroidRuntime(27516): Shutting down VM
10-03 08:39:46.025: W/dalvikvm(27516): threadid=1: thread exiting with uncaught exception (group=0x41d77300)
10-03 08:39:46.035: E/AndroidRuntime(27516): FATAL EXCEPTION: main
10-03 08:39:46.035: E/AndroidRuntime(27516): java.lang.RuntimeException: Unable to start activity ComponentInfo{cs4084.panic.button/cs4084.panic.button.ConfirmScreen}: java.lang.NullPointerException
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.ActivityThread.access$600(ActivityThread.java:140)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.os.Handler.dispatchMessage(Handler.java:99)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.os.Looper.loop(Looper.java:137)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.ActivityThread.main(ActivityThread.java:4898)
10-03 08:39:46.035: E/AndroidRuntime(27516): at java.lang.reflect.Method.invokeNative(Native Method)
10-03 08:39:46.035: E/AndroidRuntime(27516): at java.lang.reflect.Method.invoke(Method.java:511)
10-03 08:39:46.035: E/AndroidRuntime(27516): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
10-03 08:39:46.035: E/AndroidRuntime(27516): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
10-03 08:39:46.035: E/AndroidRuntime(27516): at dalvik.system.NativeStart.main(Native Method)
10-03 08:39:46.035: E/AndroidRuntime(27516): Caused by: java.lang.NullPointerException
10-03 08:39:46.035: E/AndroidRuntime(27516): at cs4084.panic.button.ConfirmScreen$GPSLocation.onPreExecute(ConfirmScreen.java:89)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.os.AsyncTask.execute(AsyncTask.java:534)
10-03 08:39:46.035: E/AndroidRuntime(27516): at cs4084.panic.button.ConfirmScreen.onCreate(ConfirmScreen.java:46)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.Activity.performCreate(Activity.java:5184)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1083)
10-03 08:39:46.035: E/AndroidRuntime(27516): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064)
10-03 08:39:46.035: E/AndroidRuntime(27516): ... 11 more
答案 0 :(得分：3)
我认为你在onPreExecute方法中得到一个空指针，所以我想locationManager为null，尝试在onCreate（）方法中初始化它。
locationManager = (LocationManager) this
.getSystemService(Context.LOCATION_SERVICE);
希望这可以解决null错误问题。
答案 1 :(得分：0)
您似乎没有实例化您的locationManager，请使用
LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
答案 2 :(得分：0)
您尚未初始化locationManager
要解决这个问题，可以在onCreate方法中执行以下操作：
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);