1.首先要熟悉fragment的生命週期

如上圖所示  當onattach呼叫時  fragment與activity發生繫結  如果此時你設定的

setOffscreenPageLimit（）小於加入的fragment 後期會呼叫ondestroyView（）方法

setUserVisibleHint（）是先於任何fragment的生命週期的 並且會呼叫每個fragment的此方法 知道某個fragment顯示後為true

當和viewpager繫結之後  會提前呼叫各個fragment的onattch oncraete oncraeteView onviewcreated等生命週期方法 

附上basefragment程式碼

也就是第一次進來的時候 通過onviewcrated去載入資料  後面tab切換的時候都是通過setUserVisibleHint()來載入資料

public abstract class BaseFragment extends android.support.v4.app.Fragment {
    private Unbinder unbinder;
    private View mContextView = null;
    protected final String TAG = "BaseFragment";

    protected boolean mIsVisible
 
;
    protected boolean mHasLoaded;
    protected boolean mHasPrepare;
    @Override
public void onCreate(@Nullable Bundle savedInstanceState) {
        LogUtils.d(TAG, "onCreate");
        super.onCreate(savedInstanceState);
//        realm = Realm.getDefaultInstance();
}

    @Override
public void onAttach(Context context) {
        super
 
.onAttach(context);

        LogUtils.d(TAG, "onAttach");
    }

    @Override
public void onStart() {
        super.onStart();
        LogUtils.d(TAG, "onStart");
    }

    @Override
public void onResume() {
        super.onResume();
        LogUtils.d(TAG, "onResume");
    }

    @Override
public void onPause() {
        super.onPause();
        LogUtils.d(TAG, "onPause");
    }

    @Override
public void onStop() {
        super.onStop();
        LogUtils.d(TAG, "onStop");
    }

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

        mContextView = inflater.inflate(bindLayout(), container, false);
        unbinder = ButterKnife.bind(this, mContextView);
        initViews(mContextView);

        return mContextView;
    }
    @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
//        LogUtils.d(TAG, "setUserVisibleHint: " + isVisibleToUser);
mIsVisible = getUserVisibleHint();
        lazyLoad();
    }
    protected void lazyLoad() {
//        LogUtils.d(TAG, "lazyLoad: mIsVisible " + mIsVisible + " mHasLoaded " + mHasLoaded + " mHasPrepare " + mHasPrepare);
if (!mIsVisible || mHasLoaded || !mHasPrepare) {
            return;
        }
//        LogUtils.d(TAG, "lazyLoad: load data in lazyLoad ");
loadData();
    }

    @Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {

        super.onViewCreated(view, savedInstanceState);
        LogUtils.d(TAG, "onViewCreated ");
        if (mIsVisible) {
            LogUtils.d(TAG, "onViewCreated: load data in #onViewCreated ");
            loadData();

        }
        mHasPrepare = true;
    }
    protected abstract int bindLayout();

    protected abstract void initViews(View mContextView);


    @Override
public void onDetach() {
        super.onDetach();
        LogUtils.d(TAG, "onDetach");
    }

    @Override
public void onDestroy() {
        LogUtils.d(TAG, "onDestroy");
        super.onDestroy();
        mHasLoaded = false;
        mHasPrepare = false;
        unbinder.unbind();
//        realm.close();
}


    public   void loadData(){
// LogUtils.d(TAG ,"-----loadData-----");
}

    @Override
public void onDestroyView() {
        LogUtils.d(TAG, "onDestroyView");
        super.onDestroyView();

    }
}