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 = ; 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