I have a simple weather app that consists of a view pager with 3 fragments (Current, Hourly and Daily weather forecast). When I launch my app for the very first time it works fine as well as I close and open it. However, I have noticed that when my app has been in the background processes for a while and then I open it, it crashes with this exception:
java.lang.NullPointerException: Attempt to read from field 'koemdzhiev.com.stormy.weather.Forecast koemdzhiev.com.stormy.ui.MainActivity.mForecast' on a null object reference
at koemdzhiev.com.stormy.ui.Current_forecast_fragment.updateDisplay(Current_forecast_fragment.java:120)
at koemdzhiev.com.stormy.ui.MainActivity$3$3.run(MainActivity.java:234)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5294)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
I suspect that this exception has something to do with the fact that I am not saving data using the saveInstance method. This is my current fragment code:
public class Current_forecast_fragment extends Fragment {
private static final String TAG = "MainActivity";
private MainActivity mActivity;
TextView mTimeLabel;
TextView mTemperatureLabel;
TextView mHumidityValue;
TextView mPrecipValue;
TextView mSummaryLabel;
TextView mLocationLabel;
TextView mWindSpeedValue;
TextView mFeelsLike;
ImageView mIconImageView;
ImageView mDegreeImageView;
public SwipeRefreshLayout mSwipeRefreshLayout;
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mActivity = ((MainActivity) getActivity());
}
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.current_forefast_fragment, container, false);
mTimeLabel = (TextView)v.findViewById(R.id.timeLabel);
mTemperatureLabel = (TextView)v.findViewById(R.id.temperatureLabel);
mHumidityValue = (TextView)v.findViewById(R.id.humidityValue);
mPrecipValue = (TextView)v.findViewById(R.id.precipValue);
mSummaryLabel = (TextView)v.findViewById(R.id.summaryLabel);
mLocationLabel = (TextView)v.findViewById(R.id.locationLabel);
mWindSpeedValue = (TextView)v.findViewById(R.id.windSpeedValue);
mFeelsLike = (TextView)v.findViewById(R.id.feels_like_label);
mIconImageView = (ImageView)v.findViewById(R.id.iconImageView);
mDegreeImageView = (ImageView)v.findViewById(R.id.degreeImageView);
mSwipeRefreshLayout = (SwipeRefreshLayout)v.findViewById(R.id.current_swipe_refresh_layout);
mSwipeRefreshLayout.setColorSchemeResources(R.color.orange, R.color.blue, R.color.green);
mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
Log.d("TAG", "Swiping in current!");
//if there is internet and if the mSwipeRefreshLayout in the Hourly and daily fragments are not already running...
if (mActivity.isNetworkAvailable()) {
if (!mActivity.mHourly_forecast_fragment.mSwipeRefreshLayout.isRefreshing() && !mActivity.mDaily_forecast_fragment.mSwipeRefreshLayout.isRefreshing()) {
if (mActivity.isLocationServicesEnabled()) {
if (mActivity.latitude != 0.0 && mActivity.longitude != 0.0) {
mActivity.getForecast(mActivity.latitude, mActivity.longitude);
} else {
mActivity.getLocation();
}
}else{
mActivity.alertForNoLocationEnabled();
}
}else{
mSwipeRefreshLayout.setRefreshing(false);
Toast.makeText(mActivity, "currently refreshing...", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(mActivity, "No Internet Connection!", Toast.LENGTH_LONG).show();
mSwipeRefreshLayout.setRefreshing(false);
}
}
});
//Start the swipe refresh layout on start up is internet available
if(mActivity.isNetworkAvailable())
mSwipeRefreshLayout.post(new Runnable() {
@Override
public void run() {
mSwipeRefreshLayout.setRefreshing(true);
Log.d("TAG","running swiping...");
}
});
return v;
}
public void updateDisplay() {
if(mActivity.mForecast != null) {
Current current = mActivity.mForecast.getCurrent();
//setting the current weather details to the ui
mTemperatureLabel.setText(current.getTemperature() + "");
mTimeLabel.setText("At " + current.getFormattedTime() + " it is");
mHumidityValue.setText(current.getHumidity() + "%");
mPrecipValue.setText(current.getPrecipChange() + "%");
mSummaryLabel.setText(current.getSummery());
mWindSpeedValue.setText(current.getWindSpeed() + "");
mFeelsLike.setText("Feels like: " + current.getFeelsLike());
mLocationLabel.setText(mActivity.locationName);
Drawable drawable = ContextCompat.getDrawable(mActivity, current.getIconId());
mIconImageView.setImageDrawable(drawable);
}else{
Toast.makeText(getActivity(),"Could not update data at this time! Please, try again.",Toast.LENGTH_LONG).show();
}
}
}
Fragment page adapter code:
public class ViewPagerAdapter extends FragmentStatePagerAdapter {
private Current_forecast_fragment mCurrent_forecast_fragment;
private Hourly_forecast_fragment mHourly_forecast_fragment;
private Daily_forecast_fragment mDaily_forecast_fragment;
CharSequence Titles[]; // This will Store the Titles of the Tabs which are Going to be passed when ViewPagerAdapter is created
int NumbOfTabs; // Store the number of tabs, this will also be passed when the ViewPagerAdapter is created
// Build a Constructor and assign the passed Values to appropriate values in the class
public ViewPagerAdapter(FragmentManager fm,CharSequence mTitles[], int mNumbOfTabsumb,Current_forecast_fragment current_fragment,
Hourly_forecast_fragment hourly_fragment,
Daily_forecast_fragment daily_fragment) {
super(fm);
this.mCurrent_forecast_fragment = current_fragment;
this.mHourly_forecast_fragment = hourly_fragment;
this.mDaily_forecast_fragment = daily_fragment;
this.Titles = mTitles;
this.NumbOfTabs = mNumbOfTabsumb;
}
//This method return the fragment for the every position in the View Pager
@Override
public Fragment getItem(int position) {
if(position == 0) // if the position is 0 we are returning the First tab
{
return this.mCurrent_forecast_fragment;
}
else if (position == 1) // As we are having 2 tabs if the position is now 0 it must be 1 so we are returning second tab
{
return this.mHourly_forecast_fragment;
}else {
return this.mDaily_forecast_fragment;
}
}
// This method return the titles for the Tabs in the Tab Strip
@Override
public CharSequence getPageTitle(int position) {
return Titles[position];
}
// This method return the Number of tabs for the tabs Strip
@Override
public int getCount() {
return NumbOfTabs;
}
}
My main activity code:
public class MainActivity extends AppCompatActivity {
...
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.mCurrent_forecast_fragment = new Current_forecast_fragment();
this.mHourly_forecast_fragment = new Hourly_forecast_fragment();
this.mDaily_forecast_fragment = new Daily_forecast_fragment();
// Creating The ViewPagerAdapter and Passing Fragment Manager, Titles fot the Tabs and Number Of Tabs.
adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs, mCurrent_forecast_fragment,
mHourly_forecast_fragment, mDaily_forecast_fragment);
// Assigning ViewPager View and setting the adapter
pager = (ViewPager) findViewById(R.id.pager);
pager.setOffscreenPageLimit(3);
pager.setAdapter(adapter);
// Assiging the Sliding Tab Layout View
tabs = (SlidingTabLayout) findViewById(R.id.tabs);
tabs.setDistributeEvenly(true); // To make the Tabs Fixed set this true, This makes the tabs Space Evenly in Available width
// Setting Custom Color for the Scroll bar indicator of the Tab View
tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
@Override
public int getIndicatorColor(int position) {
return ContextCompat.getColor(MainActivity.this, R.color.tabsScrollColor);
}
});
// Setting the ViewPager For the SlidingTabsLayout
tabs.setViewPager(pager);
}
I have this method in MainActivity which updates the data in the fragments:
public void getForecast(double latitude, double longitude) {
//scedule no response from the server task...
mScheduledFuture = exec.schedule(mNotAbleToGetWeatherDataTask,12, TimeUnit.SECONDS);
Log.d(TAG, "getForecast initiated...");
String API_KEY = "3ed3a1906736c6f6c467606bd1f91e2c";
String forecast = "https://api.forecast.io/forecast/" + API_KEY + "/" + latitude + "," + longitude + "?units=si";
if (isNetworkAvailable()) {
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(forecast)
.build();
Call call = client.newCall(request);
call.enqueue(new Callback() {
@Override
public void onFailure(Request request, IOException e) {
runOnUiThread(new Runnable() {
@Override
public void run() {
toggleSwipeRefreshLayoutsOff();
}
});
@Override
public void onResponse(Response response) throws IOException {
runOnUiThread(new Runnable() {
@Override
public void run() {
toggleSwipeRefreshLayoutsOff();
}
});
try {
String jsonData = response.body().string();
if (response.isSuccessful()) {
mForecast = parseForecastDetails(jsonData);
runOnUiThread(new Runnable() {
@Override
public void run() {
Log.d(TAG, "isSuccessful - run on UNI threth (update display)...");
//THIS LINE BELLOW CAUSES THE NPE...
mCurrent_forecast_fragment.updateDisplay();
mHourly_forecast_fragment.setUpHourlyFragment();
mDaily_forecast_fragment.setUpDailyFragment();
toggleSwipeRefreshLayoutsOff();
//set the isFirstTime to true so that the next refresh wont get location
isFirstTimeLaunchingTheApp = false;
}
});
} else {
alertUserAboutError();
}
} catch (IOException | JSONException e) {
Log.e(TAG, "Exception caught:", e);
}
}
