場(chǎng)景：

1. 第一次進(jìn)入界面
2. 左右滑動(dòng)界面

setUserVisibleHint()被調(diào)用是在onCreateView()之前，基于這個(gè)特點(diǎn)：

1. 在setUserVisibleHint()中初始化 isVisibleToUser = true卷要，表示可見了独榴，這時(shí)候調(diào)用prepareFetchData()并不會(huì)被執(zhí)行棺榔，因?yàn)閛nActivityCreated()沒初始化
2. 在onActivityCreated()中初始化 isViewInitiated = true隘道，表示生命周期被調(diào)用，這時(shí)候調(diào)用prepareFetchData()會(huì)執(zhí)行忘晤。
3. 實(shí)現(xiàn)懶加載的效果，需要數(shù)據(jù)只初始化一次设塔，所以在 prepareFetchData() 再設(shè)置一個(gè)變量 isDataInitiated = true 表示數(shù)據(jù)已經(jīng)初始化過闰蛔。
4. 這樣頁(yè)面切換后每次都會(huì)調(diào)用 setUserVisibleHint()，如果數(shù)據(jù)初始化過 isDataInitiated = true钞护， 數(shù)據(jù)就不會(huì)被再次加載

總結(jié)：每次滑動(dòng)界面都會(huì)調(diào)用setUserVisibleHint() ,在其中加載數(shù)據(jù)难咕。但是執(zhí)行這個(gè)方法需要確保 onActivityCreated() 初始化過，數(shù)據(jù)也沒有加載過

public abstract class LazyLoadFragmen extends BaseFragment {

    protected boolean isViewInitiated;
    protected boolean isVisibleToUser;
    protected boolean isDataInitiated;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.e("Fragment生命周期", "onActivityCreated");
        isViewInitiated = true;
        prepareFetchData();
    }

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        Log.e("Fragment生命周期", "setUserVisibleHint");
        this.isVisibleToUser = isVisibleToUser;
        prepareFetchData();
    }

    public abstract void fetchData();

    public boolean prepareFetchData() {
        return prepareFetchData(false);
    }

    public boolean prepareFetchData(boolean forceUpdate) {
        if (isVisibleToUser && isViewInitiated && (!isDataInitiated || forceUpdate)) {
            fetchData();
            isDataInitiated = true;
            return true;
        }
        return false;
    }

}

或

/**
 * Created by zkt on 2018-8-17.
 * Description:
 */

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.View;

/**
 * 懶加載
 */
public abstract class LazyLoadFragment extends Fragment {
    //  標(biāo)志位，標(biāo)志已經(jīng)初始化完成跨算，因?yàn)閟etUserVisibleHint是在onCreateView之前調(diào)?的，

    //  在視圖未初始化的時(shí)候步势，在lazyLoad當(dāng)中就使?的話背犯，就會(huì)有空指針的異常
    private boolean isFragmentPrepared;
    // 標(biāo)志當(dāng)前??是否可?
    private boolean isVisible;
    // 標(biāo)志數(shù)據(jù)是否加載過
    private boolean isDataPrepared;

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        //懶加載
        if (getUserVisibleHint()) {
            isVisible = true;
            onVisible();
        } else {
            isVisible = false;
            onInvisible();
        }
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        isFragmentPrepared = true;
        lazyLoad();
    }

    protected void onVisible() {
        lazyLoad();
    }

    protected void onInvisible() {
    }

    //可見 + Fragment加載過 + 數(shù)據(jù)沒加載過
    protected void lazyLoad() {
        if (isVisible && isFragmentPrepared && !isDataPrepared) {
            isDataPrepared = true;
            getData();
        }
    }

    /*  protected void lazyLoad() {
          if (!isVisible || !isPrepared) {
              return;
          }
          //數(shù)據(jù)請(qǐng)求
          getData();
      }
  */
    public abstract void getData();

}