项目场景：

项目首页使用RadioGroup+RadioButton+Fragment实现页面切换，出现了一个问题fragment会出现重叠问题，就是一个fragment显示了两层，
并不是必现问题。

经过排查发现是项目主页面Activity被销毁重建了，但是之前的fragment对象没有被回收导致。

原因分析：

在旋转屏幕后或者页面调到后台一段时间在打开，就会出现Fragment重叠显示，显示了两个相同fragment的效果。

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解决方案：

第一步，在添加fragment的时候添加key。
　第二步，再onCreate里判断savedInstanceState是否为空，若不为空说 明是重建的activity,用key将fragment对象取出来即可。
　　下面我们来看一下具体代码

    private FragmentManager fManager;private FragmentTransaction transaction;private List<Fragment> fragmentList = new ArrayList<>();private FragmentOne fragmentOne;private FragmentTwo fragmentTwo;private FragmentFour fragmentFour;private FragmentFive fragmentFive;private static final String FRAGMENT_ONE_KEY = "FragmentOne";private static final String FRAGMENT_TWO_KEY = "FragmentTwo";private static final String FRAGMENT_FOUR_KEY = "FragmentFour";private static final String FRAGMENT_FIVE_KEY = "FragmentFive";protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);fManager = getSupportFragmentManager();//如果activity销毁后重建，在这里拿出之前的Fragment对象。if (savedInstanceState != null) {fragmentOne = (FragmentOne) fManager.findFragmentByTag(FRAGMENT_ONE_KEY);fragmentTwo = (FragmentTwo) fManager.findFragmentByTag(FRAGMENT_TWO_KEY);fragmentFour = (FragmentFour) fManager.findFragmentByTag(FRAGMENT_FOUR_KEY);fragmentFive = (FragmentFive) fManager.findFragmentByTag(FRAGMENT_FIVE_KEY);initFragment(fragmentOne);initFragment(fragmentTwo);initFragment(fragmentFour);initFragment(fragmentFive);}initView();}

    private void initView() {fragmentOne = (FragmentOne) fManager.findFragmentByTag(FRAGMENT_ONE_KEY);if (fragmentOne == null) {fragmentOne = new FragmentOne();fragmentList.add(fragmentOne);hideOthersFragment(fragmentOne, true, FRAGMENT_ONE_KEY);} else {hideOthersFragment(fragmentOne, false, FRAGMENT_ONE_KEY);}radioGroup.setOnCheckedChangeListener((group, checkedId) -> {switch (checkedId) {case R.id.radio1:if (fragmentOne == null) {fragmentOne = new FragmentOne();fragmentList.add(fragmentOne);hideOthersFragment(fragmentOne, true, FRAGMENT_ONE_KEY);} else {hideOthersFragment(fragmentOne, false, FRAGMENT_ONE_KEY);}break;case R.id.radio2:if (fragmentTwo == null) {fragmentTwo = new FragmentTwo();fragmentList.add(fragmentTwo);hideOthersFragment(fragmentTwo, true, FRAGMENT_TWO_KEY);} else {hideOthersFragment(fragmentTwo, false, FRAGMENT_TWO_KEY);}break;case R.id.radio4:if (fragmentFour == null) {fragmentFour = new FragmentFour();fragmentList.add(fragmentFour);hideOthersFragment(fragmentFour, true, FRAGMENT_FOUR_KEY);} else {hideOthersFragment(fragmentFour, false, FRAGMENT_FOUR_KEY);}break;case R.id.radio5:if (fragmentFive == null) {fragmentFive = new FragmentFive();fragmentList.add(fragmentFive);hideOthersFragment(fragmentFive, true, FRAGMENT_FIVE_KEY);} else {hideOthersFragment(fragmentFive, false, FRAGMENT_FIVE_KEY);}break;}});}

下面是两个方法

 //将fragment对象添加进fragmentListpublic void initFragment(Fragment fragment) {if (fragment != null) {fragmentList.add(fragment);}}}//加载fragmentpublic void hideOthersFragment(Fragment showFragment, boolean isAdd, String key) {transaction = fManager.beginTransaction();if (isAdd) {//这里别忘了添加keytransaction.add(R.id.Frame_ID, showFragment, key);}if (ObjectUtils.isNotEmpty(fragmentList)) {for (Fragment fragment : fragmentList) {if (showFragment.equals(fragment)) {transaction.show(fragment);} else {transaction.hide(fragment);}}transaction.commit();}}

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