在我们尝试添加第二页之前，GPS类和MainActivity都正常工作。我们已经尝试过使用意图和片段，并花费了太多时间/天来试图解决这个问题。
我们在NullPointerException onClickListener()以及MainActivity类中更新任何textview时，不断获得GPS秒。我们知道它与片段的工作方式有关，但我们不确定如何解决这个问题。
这是我们的MainActivity类
public class MainActivity extends ActionBarActivity {
// Get buttons and text fields
public Button showLocation;
// TextViews
public static TextView showLatitude;
public static TextView showLongitude;
public static TextView showDistance;
// GPS class
GPS gps;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
showLocation = (Button) findViewById(R.id.btnShowLocation);
showLatitude = (TextView) findViewById(R.id.txtLatitude);
showLongitude = (TextView) findViewById(R.id.txtLongitude);
showDistance = (TextView) findViewById(R.id.txtDisplayDistance);
// Create gps
gps = new GPS(MainActivity.this);
// show location button click event
showLocation.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
gps.setTotalDistance(0.0);
}
});//END LISTENER
}// END ONCREATE
public void nextPage(View view) {
// In response to button
Intent intent = new Intent(this, ResourcePage.class);
// Set activity intent
startActivity(intent);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
}
这是GPS课程
public class GPS extends Service implements LocationListener {
private final Context mContext;
// Flag for GPS/Network/Location status
boolean isGPSEnabled = false;
boolean isNetworkEnabled = false;
boolean canGetLocation = false;
// Location Class
Location location;
// Latitude and longitude save points
private double startLatitude = 0;
private double endLatitude = 1.0;
private double startLongitude = 0;
private double endLongitude = 1.0;
private double totalDistance = 0;
// Results Array
private float[] results = new float[1];
// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_FOR_UPDATES = 10; // meters
// The minimum time between updates in milliseconds
private static final long MIN_TIME_BETWEEN_UPDATES = 1000; // 1 second
// Location Manager
protected LocationManager locationManager;
// Interface
public GPS(Context context) {
this.mContext = context;
getLocation();
}
public Location getLocation() {
try {
locationManager = (LocationManager) mContext.getSystemService(LOCATION_SERVICE);
// Getting GPS status
isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
// Getting network status
isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
// Checking Flags
if (!isGPSEnabled && !isNetworkEnabled) {
// ^no network provider is enabled do nothing/go on^
}
else {
this.canGetLocation = true;
// First get location from Network Provider
if (isNetworkEnabled) {
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, MIN_TIME_BETWEEN_UPDATES, MIN_DISTANCE_FOR_UPDATES, this);
Log.d("Network", "Network");
if (locationManager != null) {
location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (location != null) {
startLatitude = location.getLatitude();
startLongitude = location.getLongitude();
} //END OF LAST IF BLOCK
} //END OF SECOND IF BLOCK
} //END OF "FIRST" IF BLOCK
// if GPS Enabled get latitude/longitude using GPS Services
if (isGPSEnabled) {
if (location == null) {
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, MIN_TIME_BETWEEN_UPDATES, MIN_DISTANCE_FOR_UPDATES, this);
Log.d("GPS Enabled", "GPS Enabled");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
startLatitude = location.getLatitude();
startLongitude = location.getLongitude();
}
}
}
}
}//END OF ELSE BLOCK
} catch (Exception e) {
e.printStackTrace();
}
return location;
}
// Call to remove updates from listener
public void stopUsingGPS(){
if(locationManager != null){
locationManager.removeUpdates(GPS.this);
}
}
public double getLatitude(){
if(location != null){
startLatitude = location.getLatitude();
}
// Return latitude
return startLatitude;
}
public double getLongitude(){
if(location != null){
startLongitude = location.getLongitude();
}
// Return longitude
return startLongitude;
}
//Function to check GPS/wifi are enabled
public boolean canGetLocation() {
//return boolean
return this.canGetLocation;
}
// Function to show settings alert dialog if gps is off
public void showSettingsAlert(){
// On pressing Settings button will launch Settings Options
AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
// Setting Dialog Title
alertDialog.setTitle("GPS settings");
// Setting Dialog Message
alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");
// Settings button listener/press
alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
mContext.startActivity(intent);
}
});
// on pressing cancel button
alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
// Showing Alert Message
alertDialog.show();
}
// Called from listener on gps change of X
@Override
public void onLocationChanged(Location location) {
//Display Latitude and Longitude
if(location != null){
startLatitude = location.getLatitude();
startLongitude = location.getLongitude();
MainActivity.showLatitude.setText(String.valueOf(startLatitude));
MainActivity.showLongitude.setText(String.valueOf(startLongitude));
}
// Get distance between
Location.distanceBetween(startLatitude, startLongitude, endLatitude,endLongitude, results);
// Convert to miles Add distance to total
totalDistance = totalDistance + results[0] * 0.000621371192;
// Display the total
MainActivity.showDistance.setText(String.format("%.2f", totalDistance));
// Move old values to End locations
endLatitude = startLatitude;
endLongitude = startLongitude;
}
// Function to clear total distance (Testing)
public void setTotalDistance(Double savedData){
totalDistance = savedData;
MainActivity.showDistance.setText(String.valueOf(totalDistance));
}
public double getTotalDistance(){
return totalDistance;
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public IBinder onBind(Intent intent) {
// TODO Auto-generated method stub
return null;
}
}
对于layout文件，我们activity_main.xml为空fragment_main.xml，其中包含我们的所有文本字段和button s，然后fragment_resource.xml没有任何内容但是textview所以我们知道事情会出现在它上面。
答案 0 :(得分：1)
如果您说您的所有视图都属于该片段，则初始化片段中的视图而不是Activity。
活动布局没有视图，findViewById在当前的膨胀布局中查找视图。因此，当您使用视图对象时，初始化将导致NullPointerException失败。
TextView showLatitude;
TextView showLongitude;
TextView showDistance;
GPS gps;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
showLocation = (Button)rootView.findViewById(R.id.btnShowLocation);
showLatitude = (TextView) rootView.findViewById(R.id.txtLatitude);
showLongitude = (TextView) rootView.findViewById(R.id.txtLongitude);
showDistance = (TextView) rootView.findViewById(R.id.txtDisplayDistance);
gps = new GPS(getActivity()); // wrong bind the service to the activtiy
showLocation.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
gps.setTotalDistance(0.0); // remove this
}
});
return rootView;
}
你也有
public class GPS extends Service
它是一个服务类。您需要将服务绑定到Activity。但你做gps = new GPS(getActivity());
答案 1 :(得分：0)
替换它：
setContentView(R.layout.activity_main);
人：
setContentView(R.layout.fragment_main);
答案 2 :(得分：0)
你有这个方法的问题
public void setTotalDistance(Double savedData){
totalDistance = savedData;
MainActivity.showDistance.setText(String.valueOf(totalDistance));
}
你不能只调用它会返回NULL的MainActivity showDistance变量的指针异常。因为它不是静态的 所以你想这样做。
public void setTotalDistance(Double savedData){
totalDistance = savedData;
((this.mContext)MainActivity).showDistance.setText(String.valueOf(totalDistance));
}
这肯定会有所帮助。