多个Fragment在屏幕翻转会重影问题的解决

fragment使用add和hide而不用replace的方法添加到activity中，如果屏幕翻转可能会又add新的fragment进去，所以会重影。

如果有一个sparsearray保存fragment，那么在初始化的时候就应该用

private void initFragment(Bundle savedInstanceState) {
//set up fragments
//        fragments.append(MAIN_INDEX, MainFragment.newInstance());
//        fragments.append(SUCCESS_INDEX, SuccessFragment.newInstance());
//        fragments.append(FAILED_INDEX, FailedFragment.newInstance());
//        fragments.append(NONE_INDEX, NoneFragment.newInstance());
fragments = new SparseArray<>();
//Main Fragment
Fragment mainFragment = getSupportFragmentManager().findFragmentByTag(String.valueOf(MAIN_INDEX));
if (mainFragment == null) {
mainFragment = MainFragment.newInstance();
}
fragments.append(MAIN_INDEX, mainFragment);
//Success Fragment
Fragment succcessFragment = getSupportFragmentManager().findFragmentByTag(String.valueOf(SUCCESS_INDEX));
if (succcessFragment == null) {
succcessFragment = SuccessFragment.newInstance();
}
fragments.append(SUCCESS_INDEX, succcessFragment);
//Failed Fragment
Fragment failedFragment = getSupportFragmentManager().findFragmentByTag(String.valueOf(FAILED_INDEX));
if (failedFragment == null) {
failedFragment = FailedFragment.newInstance();
}
fragments.append(FAILED_INDEX, failedFragment);
//none Fragment
Fragment noneFragment = getSupportFragmentManager().findFragmentByTag(String.valueOf(NONE_INDEX));
if (noneFragment == null) {
noneFragment = NoneFragment.newInstance();
}
fragments.append(NONE_INDEX, noneFragment);
//add to activity
for (int i = 0; i < fragments.size(); i++) {
Fragment f = fragments.valueAt(i);
if (!f.isAdded())
getSupportFragmentManager()
.beginTransaction()
.add(R.id.container, f, String.valueOf(fragments.keyAt(i)))
.hide(f)
.commit();
}
}

不直接append新的fragment，而是通过fragmentsupportmanager先检查有没有已有的fragment，这样就可以解决重影问题。

需要注意的是：setRetainInstance（true）必须设置，这样fragment才不会在manager中销毁，替换fragment后想修改数据才不会出现nullpointerexception错误