我有一个简单的应用程序，包含一个MainActivity和3个片段。在每个片段中，我有一个SwipeRefreshLayout。在大多数情况下，当我的应用程序加载一切正常。但是，我注意到当android决定杀死我的应用程序然后我打开它会导致空指针异常。 OnStart我正在向服务器发出HTTP请求，而在响应方法“toggleSwipeRefreshLayoutsOff”正在导致NPE。不幸的是，我没有日志，因为它不会每次都发生：
runOnUiThread(new Runnable() {
@Override
public void run() {
toggleSwipeRefreshLayoutsOff();
}
});
这是我的toggleSwipeRefreshLayputsOff方法代码：
public void toggleSwipeRefreshLayoutsOff() {
mHourly_forecast_fragment.mSwipeRefreshLayout.setRefreshing(false);
mCurrent_forecast_fragment.mSwipeRefreshLayout.setRefreshing(false);
mDaily_forecast_fragment.mSwipeRefreshLayout.setRefreshing(false);
}
这是我的mainActivity代码：
public class MainActivity extends AppCompatActivity {
ViewPager pager;
ViewPagerAdapter adapter;
SlidingTabLayout tabs;
CharSequence Titles[] = {"Current", "Hourly", "Daily"};
int Numboftabs = 3;
Current_forecast_fragment mCurrent_forecast_fragment;
Hourly_forecast_fragment mHourly_forecast_fragment;
Daily_forecast_fragment mDaily_forecast_fragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//-----------MY CODE STARTS HERE-----------------
request = LocationRequest.create()
.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY)
.setSmallestDisplacement(1000)
.setFastestInterval(10 * 1000)
.setInterval(30 * 60 * 1000);
locationProvider = new ReactiveLocationProvider(this);
mainActivityLayout = (LinearLayout)findViewById(R.id.main_activity_layout);
changeWindowTopColor();
this.mCurrent_forecast_fragment = new Current_forecast_fragment();
this.mHourly_forecast_fragment = new Hourly_forecast_fragment();
this.mDaily_forecast_fragment = new Daily_forecast_fragment();
locationListner = new MyLocationListener();
// 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);
}
@Override
protected void onResume() {
super.onResume();
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
if (locationManager == null) {
getLocation();
Log.d(TAG, "OnResume locationManager == null");
}
}
@Override
protected void onStart() {
super.onStart();
if(isFirstTimeLaunchingTheApp) {
Log.d(TAG, "onStart getLocation");
getLocation();
}
}
@Override
protected void onPause() {
super.onPause();
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
if(locationManager != null) {
locationManager.removeUpdates(locationListner);
Log.d(TAG,"removeUpdates - onPause()");
}
//subscribe for background location updates...
subscription = locationProvider.getUpdatedLocation(request)
.subscribe(new Action1<Location>() {
@Override
public void call(Location location) {
Log.d(TAG, "Getting Background updates...");
MainActivity.this.latitude = location.getLatitude();
MainActivity.this.longitude = location.getLongitude();
}
});
}
@Override
protected void onDestroy() {
Log.d(TAG, "OnDestroy Called!");
subscription.unsubscribe();
super.onDestroy();
}
这是有问题的代码和平
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=auto";
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();
}
});
//on response from the server cansel the noResponseFromServer task
//on response from the server cansel the noResponseFromServer task
Log.d(TAG,"OnFailure_ scheduledFuture is CANCELED");
mScheduledFuture.cancel(true);
alertUserAboutError();
}
//when the call to the Okhttp library finishes, than calls this method:
@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)...");
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);
}
//on response from the server cansel the noResponseFromServer task
Log.d(TAG,"OnResponse_ scheduledFuture is CANCELED");
mScheduledFuture.cancel(true);
}
});
} else {
toggleSwipeRefreshLayoutsOff();
alertForNoInternet();
Log.d(TAG,"Alert No Internet" + 220);
//is there is no internet cancel the noResponseFromServer task
Log.d(TAG,"No internet _ scheduledFuture is CANCELED");
mScheduledFuture.cancel(true);
}
}
这是我的一个片段中的代码（它们在所有片段中非常相似）
public class Current_forecast_fragment extends Fragment {
private MainActivity mActivity;
TextView mTimeLabel;
TextView mTemperatureLabel;
TextView mHumidityValue;
TextView mPrecipValue;
TextView mSummaryLabel;
TextView mLocationLabel;
TextView mWindSpeedValue;
ImageView mIconImageView;
ImageView mDegreeImageView;
public SwipeRefreshLayout mSwipeRefreshLayout;
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mActivity = ((MainActivity) getActivity());
// Log.d(mActivity.getClass().getSimpleName(),"OnCreateFragment");
}
@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);
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);
}
我的查看寻呼机适配器代码：
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;
}
}