[英]ViewPager and dynamic fragments : re-instaciation gives NPE
I faced an issue with ViewPager and ViewPagerAdapter in Android. 我在Android中遇到了ViewPager和ViewPagerAdapter问题。 I use a viewpager with 2 static fragments (one using a textEdit and the second one using a listview). 我将viewpager与2个静态片段一起使用(一个使用textEdit,第二个使用listview)。 Theyr are working pretty good. Theyr的表现不错。 But i have a problem with the third fragment which is dynamic. 但是我对动态的第三个片段有疑问。 It uses the camera and has to be instanciated, destroyed, re-instanciated following a scenario. 它使用相机,必须根据场景进行实例化,销毁和重新实例化。 So, the ViewPagerAdapter could contain 2 or 3 framents. 因此,ViewPagerAdapter可以包含2或3个frament。 The problem appears when I re-instaciate the third fragment, I got a NPE after OnCreateView() (the main layout view is null after this method, but is not null inside the method). 当我重新安装第三个片段时,出现了问题,我在OnCreateView()之后得到了NPE(此方法后主布局视图为null,但在方法内部不为null)。
There is the code for the main activity : 有用于主要活动的代码:
mViewPager = (ViewPager) findViewById(R.id.viewpager);
setupViewPager();
mTabLayout = (TabLayout) findViewById(R.id.tabs);
mTabLayout.setupWithViewPager(mViewPager);
The setupViewPager() : setupViewPager():
private void setupViewPager() {
mViewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());
mTabFragmentDocument = new TabFragmentDocument();
mTabFragmentDocument.setApp(this);
mTabFragmentText = new TabFragmentText();
mTabFragmentText.setApp(this);
mViewPagerAdapter.addFragment(mTabFragmentText, AbstractDefiner.TEXT);
mViewPagerAdapter.addFragment(mTabFragmentDocument, AbstractDefiner.DOCUMENT);
mViewPager.setAdapter(mViewPagerAdapter);
}
To create the third fragment : 创建第三个片段:
mTabFragment = new TabFragment();
mTabFragment .setApp(this);
mViewPagerAdapter.addFragment(mTabFragment, "THIRD");
mViewPagerAdapter.notifyDataSetChanged();
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
mViewPager.setCurrentItem(2);
mViewPagerAdapter.notifyDataSetChanged();
mTabFragment .setParams(tmp[1], tmp[2], tmp[3], tmp[4]);
mTabFragment .setupView();
mTabFragment .startWork();
}
}, 1000);
And to destroy it : 并销毁它:
mViewPager.setCurrentItem(0);
mViewPager.removeViewAt(2);
mTabFragment .onDestroy();
mViewPagerAdapter.remove(2);
mViewPagerAdapter.notifyDataSetChanged();
mTabFragment = null;
Then, the Adapter code : 然后,适配器代码:
static class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
@Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
@Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
public void remove(int index) {
mFragmentList.remove(index);
mFragmentTitleList.remove(index);
}
@Override
public int getItemPosition(Object object) {
return PagerAdapter.POSITION_NONE;
}
@Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
Finally, the code of the third fragment : 最后,第三个片段的代码:
public class TabFragment extends Fragment implements SurfaceHolder.Callback,
GLSurfaceView.Renderer {
private static final String LOGCAT = "WEB_RTC_VISIO";
private HomeActivity mApp;
private String p1;
private String p2;
private String p3;
private String p4;
private VideoSource mLocalVideoSource;
private VideoRenderer.Callbacks mLocalRenderer;
private VideoRenderer.Callbacks mRemoteRenderer;
private GLSurfaceView mVideoView;
private SurfaceView mDrawView;
private SurfaceHolder mDrawHolder;
private ImageView mCursor;
private String mBgBytesString;
private ImageView mImgView;
private View mV;
public TabFragment() {
// Required empty public constructor
}
public void setApp(HomeActivity app) {
mApp = app;
}
public void setParams(String p1, String p2, String p3,
String p4) {
this.p1= p1;
this.p2= p2;
this.p4= p4;
this.p3= p3;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
mV = inflater.inflate(R.layout.third_layout, container, false);
return mV;
}
@Override
public void onDetach() {
super.onDetach();
}
public void setupView() {
RequestUserPermission requestUserPermission = new RequestUserPermission(mApp);
requestUserPermission.verifyStoragePermissions();
mImgView = (ImageView) mV.findViewById(R.id.img_display); // NPE HERE
TextView mTest1= (TextView) mV.findViewById(R.id.test1);
mRequestLabelTextView.setText("test 1");
TextView mTest2= (TextView) mV.findViewById(R.id.test2);
mEquipmentSerialTextView.setText("test 2");
// View that displays the view from the camera
mVideoView = (GLSurfaceView) mV.findViewById(R.id.gl_surface);
// View that displays the cursor and drawing associated
mDrawView = (SurfaceView) mV.findViewById(R.id.draw_surface);
mDrawHolder = mDrawView.getHolder();
mDrawHolder.setFormat(PixelFormat.TRANSPARENT);
mDrawHolder.addCallback(this);
// Image of the cursor
mCursor = (ImageView) mV.findViewById(R.id.mouseCursor);
// Some more inits
}
public void startWork() {
//SOME WORK
}
}
So, the first instanciation is ok, but at the second, I got the NPE on getting the ImageView... Someone can help me understanding this problem please ? 因此,第一个实例是可以的,但是第二个实例上,我得到了NPE上的ImageView ...有人可以帮助我理解这个问题吗?
Thanks in advance ! 提前致谢 !
Try using FragmentStatePagerAdapter
not FragmentPagerAdapter
it will solve many problems. 尝试使用FragmentStatePagerAdapter
而不是FragmentPagerAdapter
会解决很多问题。 Hope it will gonna work for you too. 希望它也能为您服务。
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