我已經在各處搜索了,但還沒有解決我的問題。Android ArrayAdapter在ViewPager中使用時會導致NullPointerException
我在Activity中使用ViewPager。 ViewPager包含3個片段:一個是普通片段,第二個片段包含自定義ListView,第三個片段是MapFragment(SupportMapFragment)。
我只使用支持片段。
問題是在活動嘗試填充設置適配器和地圖上的標記的片段後,將調用ViewPager適配器(FragmentPagerAdapter)的getItem()方法。
所以,我triyng初始化ViewPager之前初始化片段,使用用於片段一個單模式:
在活動的onCreate():
setContentView(R.layout.act_discover_small);
profiloFragment = new ProfiloFragment();
mapFragment = new MappaMonumentiFragment();
elencoFragment = new ElencoMonumentiFragment();
initViewPager();
的initViewPager()方法是:
private void initViewPager() {
mPagerAdapter = new PagerAdapter(getSupportFragmentManager());
mViewPager = (SmartViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mPagerAdapter);
mViewPager.setOffscreenPageLimit(3);
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
if (!beginSwipe)
elencoFragment.List.finishRefresh();
beginSwipe = true;
}
@Override
public void onPageScrollStateChanged(int arg0) {
}
@Override
public void onPageSelected(int arg0) {
beginSwipe = false;
lockDrawer(arg0);
if (arg0 == 0) {
swipe_left_button.setText("show map");
} else {
swipe_left_button.setText("show list");
}
}
});
}
這是ViewPager適配器
class PagerAdapter extends FragmentPagerAdapter {
public PagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public int getCount() {
return 3;
}
@Override
public Fragment getItem(int i) {
Log.i(TAG, "getItem viewpager n." + i);
switch (i) {
case 0:
if (profiloFragment == null)
profiloFragment = new ProfiloFragment();
return profiloFragment;
case 1:
if (elencoFragment == null)
elencoFragment = new ElencoMonumentiFragment();
return elencoFragment;
case 2:
if (mapFragment == null)
mapFragment = new MappaMonumentiFragment();
return mapFragment;
}
return null;
}
}
我得到triyng以填充與所述元件的第二個片段的一個ArrayAdapter在該方法中,當(在onPostExecute(執行)的的AsyncTask的)一個NullPointerException:
public void populateElencoMonumenti(List<SmartPlace> placesList) {
if (placesList != null) {
places = (ArrayList<SmartPlace>) placesList;
//before: adapter.clear(); //NullPointerException at this line
//after:
if (adapter == null) {
adapter = new ElencoMonumentiAdapter(ctx, act, app);
}
adapter.addAll(places);
List.setAdapter(adapter);
} else {
adapter.clear();
List.setAdapter(adapter);
}
}
如果我登錄(適配器== null)在調用adapter.clear()之前它返回true,所以它是空的。
如果我嘗試檢查它是否是空並重新初始化它,我得到了NPE在適配器的構造:
public ElencoMonumentiAdapter(Context ctx, Discover homAct, SmartApplication app) {
// super(ctx, R.layout.list_row_monument);
super(ctx, R.layout.list_row_monument, new ArrayList<SmartPlace>()); //NPE here
Log.e(TAG, "null ctx? " + (ctx == null));
this.app = app;
this.ctx = ctx;
}
堆棧跟蹤是:
12-18 11:13:07.285: E/AndroidRuntime(20865): FATAL EXCEPTION: main
12-18 11:13:07.285: E/AndroidRuntime(20865): Process: com.Thinple.MiWalks.ui, PID: 20865
12-18 11:13:07.285: E/AndroidRuntime(20865): java.lang.NullPointerException
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.widget.ArrayAdapter.init(ArrayAdapter.java:310)
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:153)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.Thinple.MiWalks.ui.adapters.ElencoMonumentiAdapter.<init>(ElencoMonumentiAdapter.java:41)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.Thinple.MiWalks.ui.fragments.ElencoMonumentiFragment.populateElencoMonumenti(ElencoMonumentiFragment.java:129)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.Thinple.MiWalks.ui.Discover.notifyFragments(Discover.java:328)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.Thinple.MiWalks.ui.Discover.populatePlaces(Discover.java:509)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.Thinple.MiWalks.threading.tasks.GetPlacesFromDBtask.onPostExecute(GetPlacesFromDBtask.java:53)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.Thinple.MiWalks.threading.tasks.GetPlacesFromDBtask.onPostExecute(GetPlacesFromDBtask.java:1)
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.os.AsyncTask.finish(AsyncTask.java:632)
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.os.AsyncTask.access$600(AsyncTask.java:177)
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.os.Handler.dispatchMessage(Handler.java:102)
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.os.Looper.loop(Looper.java:136)
12-18 11:13:07.285: E/AndroidRuntime(20865): at android.app.ActivityThread.main(ActivityThread.java:5017)
12-18 11:13:07.285: E/AndroidRuntime(20865): at java.lang.reflect.Method.invokeNative(Native Method)
12-18 11:13:07.285: E/AndroidRuntime(20865): at java.lang.reflect.Method.invoke(Method.java:515)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-18 11:13:07.285: E/AndroidRuntime(20865): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-18 11:13:07.285: E/AndroidRuntime(20865): at dalvik.system.NativeStart.main(Native Method)
我真的不覺得一個辦法。
在此先感謝您的回覆。
適配器爲null,則它聲明和初始化在哪裏? – Raghunandan
在片段onStart()我這樣做: \t \t adapter = new ElencoMonumentiAdapter(ctx,act,app); \t \t List.setAdapter(adapter); (TAG,「adapter null?」+(adapter == null)); 和日誌打印false ..所以它不是空! 編輯:我試圖在onAttach()或onCreateView()中移動該代碼alson,但它沒有奏效。 –
它是空的,如果不是你不會NPE在線。順便問一下,ctx是什麼 – Raghunandan