Fragment lazy load

First, talk about something else ： I bought my train ticket home today ,12306 Still didn't disappoint me , Decisively did not grab . I bought a plane ticket first , Then wait for tomorrow's train ticket , If you get it, you'll refund the plane ticket , Or you'll have to take a plane .

Record today Fragment Lazy loading

About Fragment Lazy loading of has the following two points to declare first ：

1.Fragment Of setUserVisibleHint Method , Only Fragment stay ViewPager Will be called

// If isVisibleToUser by true, Indicates that the current interface is visible to the user 
 @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);

    }

2.Fragment Of setUserVisibleHint Execution in onCreateView Before

Lazy loading ：Fragment stay ViewPager When used in , When Fragment Load data only when it is visible to the user , This can reduce Activity Resources required for startup , Think about it , Once started Activity, There are more than one Fragment Load data together , It definitely needs a lot of resources .

Implementation steps

1. Definition BaseLazyFrament

public abstract class BaseLazyFragment extends Fragment {
    

    protected String TAG = getClass().getSimpleName();

    // Mark whether the layout has been initialized 
    protected boolean isViewCreated;
    // Mark whether data has been loaded 
    protected boolean isLoadDataCompleted;
    /** *  Statement rootView, When Fragment call  onCreateView  Created on rootView, *  When Fragment Switch to invisible and call  onDestroyView  When destroying views , *  This rootView It's not going to be destroyed . When Fragment  Switch back and call onCreateView Recreate the view  *  Of   When , Go straight back to rootView. */
    protected View rootView;
    // This is used to display data in subclasses 
    protected RecyclerView rv;

    public BaseLazyFragment() {
    }

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        Log.e(TAG, "isVisibleToUser=" + isVisibleToUser);
        // If at present Fragment so ,onCreateView  Has been called , And no data has been loaded , Then load data 
        if (isVisibleToUser && isViewCreated && !isLoadDataCompleted) {
            lazyLoadData();
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        if (rootView == null) {
            rootView = inflater.inflate(getLayout(), container, false);
            ButterKnife.bind(this, rootView);
            init(rootView);
            //isViewCreated  Set as  true
            isViewCreated = true;
        }
        return rootView;
    }

    /** * *  Here we need to call once lazyLoadData , because ViewPage When showing the first page setUserVisibleHint *  Precede  onCreateView call , Now  isViewCreated  by false, No data will be loaded . * onActivityCreated  stay  onCreateView  Then call , At this time, the view has been initialized  *  BI  isViewCreated  by  true, So we load data here , Make sure the first page Fragment Normal display  */
    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        if (getUserVisibleHint()) {
            lazyLoadData();
        }
    }

    // Get the layout file 
    protected abstract int getLayout();

    // Initialize some view And related data 
    protected abstract void init(View view);

    // Load data 
    protected void lazyLoadData() {
        isLoadDataCompleted = true;
    }

}

The code uses ButterKnife Conduct view binding , There's a point to make ： Statement Member variables rootView, For preservation Fragment The view of , If in onCreateView Declare local variables rootView（ As shown below ）, So in Fragment call onDestroyView in the future , The user switches back onCreateView Call again , It can lead to some problems .

  @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView= inflater.inflate(R.layout.f1, container,false);
        return rootView;
    }

for instance ： In the beginning ,Fragment For the first time ,Fragment There is one of them. RecylerView, We set a adapter. Then we switch Fragment, Leading to the current Fragment invisible , And the view is destroyed . Then when we switch back ,Fragment The view will be recreated （ call onCreateView）, Then we call adapter.notifyDataSetChanged(); Find it completely useless . Because after we recreate the view , Will recreate RecylerView example . This RecylerView It's not what we set adapter Of RecylerView 了 , So call adapter.notifyDataSetChanged() It doesn't work at all . About calling adapter.notifyDataSetChanged() For a more detailed discussion of what doesn't work, see here RecyclerView encounter notifyDataSetChanged Solution when invalid

2. It's over BaseLazyFrament, Then we define Fragment It is basically OK to realize it , In the following code getData Method in lazyLoadData Call in , Simulate loading data .

public class FirstLazyFragment extends BaseLazyFragment {
    

    public static final String ID = "ID";
    protected String TAG = getClass().getSimpleName();
    @BindView(R.id.ptr_rv)
    PullToRefreshRecyclerView pullToRefreshRecyclerView;
    @BindView(R.id.tv_title)
    TextView tvTitle;

    private int id = -1;

    private List<NotifyBean> data;
    private NotifyAdapter adapter;

    public FirstLazyFragment() {
        // Required empty public constructor
    }

    public static FirstLazyFragment newInstance(int id) {
        FirstLazyFragment fragment = new FirstLazyFragment();
        Bundle args = new Bundle();
        args.putInt(ID, id);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            id = getArguments().getInt(ID);
        }
    }

    @Override
    protected int getLayout() {
        return R.layout.fragment_lazy;
    }

    @Override
    protected void init(View view) {
        Log.e(TAG, "onCreateView init id=" + id);
        tvTitle.setText("fragment id is " + id);
        data = new ArrayList<>();
        rv = pullToRefreshRecyclerView.getRefreshableView();
        rv.setLayoutManager(new LinearLayoutManager(getContext()));
        adapter = new NotifyAdapter(data);
        rv.setAdapter(adapter);
        pullToRefreshRecyclerView.setOnRefreshListener(new PullToRefreshBase.OnRefreshListener<RecyclerView>() {
            @Override
            public void onRefresh(PullToRefreshBase<RecyclerView> refreshView) {
                getData();
            }
        });
    }

    @Override
    protected void lazyLoadData() {
        super.lazyLoadData();
        Log.e(TAG, "lazyLoadData id=" + id);
        getData();
    }

    private void getData() {
        pullToRefreshRecyclerView.postDelayed(new Runnable() {
            @Override
            public void run() {
                pullToRefreshRecyclerView.onRefreshComplete();
                if (page <= 3) {
                    List<NotifyBean> tempList = new ArrayList<>();
                    for (int i = 0; i < 10; i++) {
                        NotifyBean notifyBean = new NotifyBean(System.currentTimeMillis() / 1000, "page" + page + "i=" + i);
                        tempList.add(notifyBean);
                    }
                    data.addAll(tempList);
                    page++;
                    adapter.notifyDataSetChanged();
                } else {
                    Toast.makeText(getContext(), getString(R.string.load_all), Toast.LENGTH_SHORT).show();
                    pullToRefreshRecyclerView.setMode(PullToRefreshBase.Mode.DISABLED);
                }
            }
        }, 500);
    }
}

3. Don't forget , Lazy loading is Fragment stay ViewPager Used in . Definition ViewPager Adapter for

public class ViewPagerAdapter extends FragmentStatePagerAdapter {
    

    private List<Fragment> fragments;

    public ViewPagerAdapter(FragmentManager fm, List<Fragment> fragments) {
        super(fm);
        this.fragments = fragments;
    }

    @Override
    public Fragment getItem(int position) {
        return fragments.get(position);
    }

    @Override
    public int getCount() {
        return fragments.size();
    }

}

4. stay Activity Use in

public class LazyLoadActivity extends AppCompatActivity {
    

    @BindView(R.id.view_page)
    ViewPager viewPage;
    private List<Fragment> fragments;

    public static void launch(Context context) {
        Intent intent = new Intent(context, LazyLoadActivity.class);
        context.startActivity(intent);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_lazy_load);
        ButterKnife.bind(this);
        fragments = new ArrayList<>();
        fragments.add(FirstLazyFragment.newInstance((1)));
        fragments.add(SecondLazyFragment.newInstance((2)));
        fragments.add(ThirdLazyFragment.newInstance((3)));
        fragments.add(ForthLazyFragment.newInstance((4)));
        viewPage.setAdapter(new ViewPagerAdapter(getSupportFragmentManager(), fragments));
    }
}

For the complete code, please move to ：https://github.com/humanheima/FragmentUseDemo, The following sentence is very important

demo Medium lazyload Under the folder is all the code for lazy loading

Reference link
1.https://www.jianshu.com/p/8a0f6b627e37
2.http://www.10tiao.com/html/169/201608/2650820834/1.html
3.http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2014/1021/1813.html