Fragment 懒加载

因为项目中经常用到tabLayout + viewpager 结合使用，页面切换时要用到延迟加载的情况，所以单独写出一个demo，方便查看和便于使用

1.首先新建一个BaseLazyFragment

/**
 * Created by xuqianqian on 2018/2/28.
 */
public  abstract class BaseLazyFragment extends Fragment {

    protected View mRootView;
    public Context mContext;
    protected boolean isVisible;
    private boolean isPrepared;
    private boolean isLoad = false;

    //最先执行
    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        if (getUserVisibleHint()) {//当前显示
            isVisible = true;
            if(!isLoad){
                lazyLoad();
            }
        } else {
            isVisible = false;
            //onInvisible();
        }
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mContext = getActivity();
        setHasOptionsMenu(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        if (mRootView == null) {
            mRootView = getLayout();
        }
        return mRootView;
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        isPrepared = true;
        //如果已经加载过了，就无需再重新加载
        if(!isLoad){
            lazyLoad();
        }
    }

    /**
     * 懒加载
     */
    protected void lazyLoad() {
        if (!isPrepared || !isVisible) {
            return;
        }
        isLoad = true;
        initData();
    }

//    protected void onInvisible() {
//
//    }
    //初始化布局View
    public abstract View getLayout();

    public abstract void initData();
}

2.让你的fragment extend BaseLazyFragment

public class GankFragment extends BaseLazyFragment {

String type;
public static GankFragment newInstance(String type) {
    GankFragment gankFragment = new GankFragment();
    Bundle bundle = new Bundle();
    bundle.putString("type", type);
    gankFragment.setArguments(bundle);
    return gankFragment;
}
//加载布局
@Override
public View getLayout() {

    type = getArguments().getString("type");
    TextView tv = new TextView(getActivity());
    tv.setText(type);
    tv.setGravity(Gravity.CENTER);
    return tv;
}

@Override
public void initData() {

    //初始化一些控件，加载网络数据
}

}

3.剩下的就是FragmentPagerAdapter了

public class TitleAdapter extends FragmentPagerAdapter {

private List<Fragment> fragments;

private List<String> types;

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

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

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

@Override
public CharSequence getPageTitle(int position) {
    return types.get(position);
}
}

MainActivity.java

private List<String> titles = new ArrayList<>();

private List<Fragment> fragments = new ArrayList<>();
TitleAdapter titleAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    TabLayout tablayout = findViewById(R.id.tablayout);
    ViewPager viewpager = findViewById(R.id.viewpager);

    titles.add("android");
    titles.add("ios");
    titles.add("web");
    titles.add("java");

    fragments.add(GankFragment.newInstance("android"));
    fragments.add(GankFragment.newInstance("ios"));
    fragments.add(GankFragment.newInstance("web"));
    fragments.add(GankFragment.newInstance("java"));

    titleAdapter = new TitleAdapter(getSupportFragmentManager(), fragments, titles);
    viewpager.setAdapter(titleAdapter);
    tablayout.setTabMode(TabLayout.MODE_FIXED);
    tablayout.setupWithViewPager(viewpager);
}

https://github.com/QQabby/LazyFragmentApplication