不使用replace方法
1.點選模組時首先hide所有fragment：

/**
 * 隱藏所有fragment
 */
private void hideAllFragment() {
    if (mTrainFragment != null) {
        mTransaction.hide(mTrainFragment);
    }
    if (mFindFragment != null) {
        mTransaction.hide(mFindFragment);
    }
}

2.然後判斷是否為空來add或者show：

@Override
public void onClick(View v) {
    mTransaction = mManager.beginTransaction
 
();
    hideAllFragment(); //隱藏所有fragment
    switch (v.getId()) {
        case R.id.train:
            selectTab(mTrainIv, mTrainTv);//模組按鈕的圖片和文字變化
            if (mTrainFragment == null) {
                mTrainFragment = TrainFragment.getInstance();
                mTransaction.add(R.id.fragment_layout, mTrainFragment);
 

            } else {
                mTransaction.show(mTrainFragment);
            }
            break;
        case R.id.find:
            selectTab(mFindIv, mFindTv);
            if (mFindFragment == null) {
                mFindFragment = FindFragment.getInstance();
                mTransaction.add
 
(R.id.fragment_layout, mFindFragment);
            } else {
                mTransaction.show(mFindFragment);
            }
            break;
    }
    mTransaction.commit();
}

3.fragment使用單例：

private static FindFragment fragment = null;

public static FindFragment getInstance() {
    if (fragment == null) {
        fragment = new FindFragment();
    }
    return fragment;
}

4.在fragment的onCreateView方法中判斷view是否為空：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    if (view == null){
        view = inflater.inflate(R.layout.fragment_find, container, false);
        initView();
    }
    return view;
}