android - 为什么会调用fragment的onCreateView、onCreate、onActivityCreated

Question

我有一个处理片段和 ViewPager 的应用程序。我在 ViewPager 中有三个片段。当您在它们之间切换时，它总是会导致其他两个片段调用它们的 onCreateView 方法。如何只做一次，只有在创建 FragmentActivity 时才做？？？我已经阅读了一些问题并尝试了解决方案，但片段仍然具有相同的行为。

ListFragment onCreate 调用了两次
 onCreate() 和 onCreateView() 调用的次数远远超过所需（片段）

这里有一些代码，如果它对你有帮助，伙计们：

主要活动：

public class StartingActivity extends FragmentActivity implements View.OnClickListener {
ViewPager viewPager;
    CirclePageIndicator pageIndicator;

    Button discount;
    Button qrCode;
    Button pay;
    TabHost tabHost;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.starting_layout);
        viewPager = (ViewPager) findViewById(R.id.pager);

        if (savedInstanceState == null) {

            Fragment firstPage = Fragment.instantiate(this, FindTovarFragment.class.getName());
            Fragment secondPage = Fragment.instantiate(this, MainWindowActivity.class.getName());
            Fragment thirdPage = Fragment.instantiate(this, MapActivity.class.getName());

            if ((firstPage != null && !firstPage.isDetached())|| (secondPage != null && !secondPage.isDetached()) || (thirdPage != null && !thirdPage.isDetached())) {

            List<Fragment> viewPagerFragments = new ArrayList<Fragment>();
            viewPagerFragments.add(firstPage);
            viewPagerFragments.add(secondPage);
            viewPagerFragments.add(thirdPage);


            PageAdapter pageAdapter = new PageAdapter(getSupportFragmentManager(), viewPagerFragments);

            viewPager.setAdapter(pageAdapter);

            pageIndicator = (CirclePageIndicator) findViewById(R.id.circle);
            pageIndicator.setViewPager(viewPager);
            pageIndicator.setCurrentItem(pageAdapter.getCount() - 2);
            }
        }

}

地图活动：

public class MapActivity extends Fragment implements OnMyLocationListener {

    //Тэг для логов
    private static final String TAG = "MapActivity";
    List<Address> addressList;
    private static final String STRING_LOCATION = "";

    ArrayList<TorgCentr> randomTorgCentr;
    ArrayList<String> torgCentrNames;

    Context context;
    AutoCompleteTextView searchTorgCentr;
    OverlayManager overlayManager;
    MapController mapController;
    TextView textView;
    double longitude;
    double latitude;
    double itemLongitude;
    double itemLatitude;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Log.d(TAG, "MapActivity onCreateView");


        View view = (LinearLayout) inflater.inflate(R.layout.map_layout, container, false);
        final MapView mapView = (MapView) view.findViewById(R.id.map);
        textView = (TextView) view.findViewById(R.id.searchlocation);
        searchTorgCentr = (AutoCompleteTextView) view.findViewById(R.id.autoCompleteTextView);

        mapView.showBuiltInScreenButtons(true);
        mapController = mapView.getMapController();
        context = getActivity();
        return view;
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "MapActivity onCreate");

    }

    public void onActivityCreated(Bundle savedInstanceState) {
        Log.d(TAG, "MapActivity onActivityCreated");
        context = getActivity();

        SetRightMapDisplayAddress rightMapDisplayAddress = new SetRightMapDisplayAddress();
        rightMapDisplayAddress.execute(STRING_LOCATION);

        DownloadSuperMarketsArray superMarketsArray = new DownloadSuperMarketsArray();
        superMarketsArray.execute();

        overlayManager = mapController.getOverlayManager();
        overlayManager.getMyLocation().setEnabled(false);

        super.onActivityCreated(savedInstanceState);
    }

第二个片段：

public class MainWindowActivity extends Fragment {

    private static final String TAG = "MainWindowActivity";

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Log.d(TAG, "MainWindowActivity onCreateView");
        View view = (RelativeLayout) inflater.inflate(R.layout.main_window_layout, container, false);
        if (container == null) {
            return null;
        }
        return view;
    }
}

第三个：

public class FindTovarFragment extends Fragment {

    private static final String TAG= "FindTovarFragment";

    Context context;
    ArrayList<Category> categories;
    Spinner categoryContainer;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Log.d(TAG, "FindTovarFragment onCreateView");

        View view = (LinearLayout) inflater.inflate(R.layout.find_tovar_main_layout, container, false);
        categoryContainer = (Spinner) view.findViewById(R.id.category);

        return view;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.d(TAG, "FindTovarFragment onActivityCreated");
        DownloadCategory downloadCategory = new DownloadCategory();
        downloadCategory.execute();
    }

MapActivity 的日志：

06-20 11:06:37.709: DEBUG/MapActivity(1290): MapActivity onCreate
06-20 11:06:37.709: DEBUG/MapActivity(1290): MapActivity onCreateView
06-20 11:06:38.509: DEBUG/MapActivity(1290): MapActivity onActivityCreated

然后一次又一次：

06-20 11:07:53.239: DEBUG/MapActivity(1290): MapActivity onCreate
06-20 11:07:53.239: DEBUG/MapActivity(1290): MapActivity onCreateView
06-20 11:07:53.429: DEBUG/MapActivity(1290): MapActivity onActivityCreated
06-20 11:08:23.029: DEBUG/MapActivity(1290): MapActivity onCreate
06-20 11:08:23.039: DEBUG/MapActivity(1290): MapActivity onCreateView
06-20 11:08:23.269: DEBUG/MapActivity(1290): MapActivity onActivityCreated

非常感谢您提前。

score 15 · Accepted Answer

ViewPager 默认在内存中保留 1 页，到当前页的任一侧。因此，在当前页面向左/向右滑动 1 页时，它不会重新创建这些页面。但是当向左/向右滑动超过 1 个页面时，它会再次重新创建这些页面，因此称为 OnCreateView()、OnCreate()。

如果应用程序使用很少的页面 3，您可以通过调用来增加要保留的页面数，

mViewPager.setOffscreenPageLimit(2);

在这里描述

score 12 · Accepted Answer

我会在 android 开发人员文档中更改您的架构：

http://developer.android.com/reference/android/support/v4/app/FragmentPagerAdapter.html

但我会改变一些事情......

1-我会改变这个方法：

/**
     * The Fragment's UI is just a simple text view showing its
     * instance number.
     */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_pager_list, container, false);
        View tv = v.findViewById(R.id.text);
        ((TextView)tv).setText("Fragment #" + mNum);
        return v;
    }

对于这样的事情，我们根据 viewPager 的位置来决定填充哪个片段：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);

SupportFragmentManager ft = getChildFragmentManager().beginTransaction();

String tag = "";
Fragment fragment = null;

  switch (mNum) {
  case 0:
    fragment = new MyFragmentZero();
    tag = FragmentTags.TAG_0;
    break;
  case 1:
    fragment = new MyFragmentOne();
    tag = FragmentTags.TAG_3;
    break;
  case 2:
    fragment = new MyFragmentTwo();
    tag = FragmentTags.TAG_2;
    break;
  default:
    break;
  }

/*OPTIONAL We can pass arguments to the fragments
Bundle args = new Bundle();
args.putInt(Arguments.ARG_POSITION, mNum);
fragment.setArguments(args);*/

//Place the fragment in the container
ft.replace(R.id.fragment_container fragment, tag);
ft.commit();

//You need a base layout for all fragment and use nested fragments later or you can define the layout for each position(mNum) inside the switch.
return inflater.inflate(R.layout.fragment_layout_default_for_all_views, container,
    false);
}

像这样你将拥有一个很好的架构，一旦它像这样工作应该没问题。

无论如何，您必须知道 viewPager 如何在不同位置填充片段。

当您从位置 0 开始时，将创建位置 0 上的片段和位置 1 上的片段。

然后，当您滑动到位置 1 时，会在 2 位置创建片段，因此您现在在不同位置创建了三个片段（0、1、2..假设您在 viewPager 上只有 3 个页面）。

我们滑动到位置 2，最后一个，第一个位置 (0) 上的片段被销毁，所以我们现在有位置 2 和 3 上的片段。

我希望它有所帮助，如果您有任何问题，请告诉我。干杯

score 11 · Accepted Answer

最后我能够弄清楚。只需要重写destroyItem 方法，这样它就不会破坏对象。希望这对某人有用。

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    Log.d(TAG, "destroy!");
}

android - 为什么会调用fragment的onCreateView、onCreate、onActivityCreated

3 回答 3

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