方向改变导致Activity中的Fragment系列消失，不应用保存实例状态

Question

所以我在开发项目中遇到了另一个障碍。

这一次涉及到关于改变方向和保持其保存的实例状态的片段。如果它涉及两个问题，但它们涉及相同的问题催化剂，即方向变化，请原谅我。我会尽量详细，所以请多多包涵。

我有一堆片段使用单个活动作为主机。在我看来，我的片段是按部分分组的，尽管它们仍然是模块化/可按代码重用的。

所以我有 3 个片段托管在一个实现抽屉导航的片段中。逻辑流程是这样的：

Frag1 ->（按下一步）-> Frag2 ->（按下一步）-> Frag3

Frag2 和 Frag3 的创建调用 addToBackStack() 在 FragmentManager 中提交事务。 问题是当我在 Frag2 或 Frag3 然后更改设备方向时，片段消失然后显示 Frag1。

另一个问题是我在Frag1中，然后在EditText中键入一些文本，然后更改方向，尽管实现了onSaveInstanceState(Bundle bundle)，但文本消失了。

这是我的相关代码sn-ps：

在Activity.java中创建Frag1的代码sn-p

@Override
public void onNavigationDrawerItemSelected(int position) {
    // init the fragment (with a default fragment, not null)
    rootFragment = PlaceholderFragment.newInstance(position + 1);
    // Position number from navigation sidebar starts from 0.
    // Since position starts from 0, add 1 to match section number
    // as implemented in {@link #onSectionAttached()}
    switch (position) {
        case 0: // Other section
            rootFragment = PlaceholderFragment.newInstance(position + 1);
            break;
        case 1: // Frag1
            rootFragment = new AddPointsFragment().newInstance(position + 1, "");
            break;
        case 2: // Other section
            rootFragment = new CheckPointsFragment().newInstance(position + 1, "");
            break;
        default:
            break;
    }

    // update the main primary content by replacing fragments
    FragmentManager fragmentManager = getFragmentManager();

    // clear all fragments from previous section from the back stack
    fragmentManager.popBackStackImmediate(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);

    // replace all currently added fragments in container and replace with the new fragment
    // don't add to back stack since these serve as "root" fragments
    fragmentManager.beginTransaction()
            .replace(R.id.container, rootFragment, rootFragment.getClass().getName())
            .commit();
}

在Activity.java中创建Frag2的代码sn-p

public void startAddPointsSuccessFragment(int sectionNumber, String cardNo, int points) {
    // Create fragment and give it its arguments
    // Since this is not a major fragment,
    // I just used its major parent fragment (AddPointsFragment)
    // section number to follow the action bar title
    AddPointsSuccessFragment addPointsSuccessFragment =
            new AddPointsSuccessFragment().newInstance(sectionNumber, cardNo, points);
    // Replace whatever is in the container view with this fragment,
    // and add the transaction to the back stack so the user can navigate back
    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.beginTransaction()
            .replace(R.id.container, addPointsSuccessFragment)
            .addToBackStack(AddPointsSuccessFragment.class.getName())
            .commit();
}

在Activity.java中创建Frag3的代码sn-p

public void onOkButtonAddPointsSuccessFragmentInteraction(int sectionNumber, String cardNo, int points) {
    int minimumPoints = 10;
    if (points < minimumPoints) {
        // Go back to previous fragment (AddPointsFragment)
        // by simulating a back press from host activity.
        this.onBackPressed();
    }
    else {
        // Create fragment and give it its arguments
        // Since this is not a major fragment,
        // I just used its major parent fragment (AddPointsFragment)
        // section number to follow the action bar title
        RedeemRewardFragment redeemRewardFragment =
                new RedeemRewardFragment().newInstance(sectionNumber, cardNo, points);
        // Replace whatever is in the container view with this fragment,
        // and add the transaction to the back stack so the user can navigate back
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.container, redeemRewardFragment)
                .addToBackStack(RedeemRewardFragment.class.getName())
                .commit();
    }
}

关于方向改变后碎片消失的问题，我还没有想出可能的解决方案。

关于在方向改变时保存的实例状态的持久性，我尝试在 Frag1 类中实现 onSaveInstanceState(Bundle bundle)，如下所示：

AddPointsFragment.java 的代码 sn-p

EditText cardNoEditText;    

@Override
public void onSaveInstanceState(Bundle bundle) {
    super.onSaveInstanceState(bundle);
    bundle.putInt(ARG_SECTION_NUMBER, mSectionNumber);
    bundle.putString(ARG_CARD_NO, cardNoEditText.getText().toString());
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mSectionNumber = getArguments().getInt(ARG_SECTION_NUMBER);
        mCardNo = getArguments().getString(ARG_CARD_NO);
    }
    if (savedInstanceState != null) {
        mSectionNumber = savedInstanceState.getInt(ARG_SECTION_NUMBER);
        mCardNo = savedInstanceState.getString(ARG_CARD_NO);
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_add_points, container, false);
    cardNoEditText = (EditText) view.findViewById(R.id.cardNoEditText);
    cardNoEditText.setText(mCardNo);
    Button enterCardNoButton = (Button) view.findViewById(R.id.enterCardNoButton);
    enterCardNoButton.setOnClickListener(this);
    Button scanCardNoButton = (Button) view.findViewById(R.id.scanCardNoButton);
    scanCardNoButton.setOnClickListener(this);
    return view;
}

我尝试在代码中运行有关在更改方向期间失败的持久性的调试器，并且经过检查，onSaveInstanceState(Bundle bundle) 确实有效并且能够将数据传递给 EditText。但是，我还发现 Activity 在更改方向时也会调用 onNavigationDrawerItemSelected(int position)，正如您在其中的代码中看到的那样，它会擦除​​ Frag1 的 FragmentManager 并将其替换为不具有值的新 Frag1还没有卡。

我想这里的基本问题是在这种情况下实现 onSaveInstanceState(Bundle bundle) 的最佳方式是什么？我尝试在 Fragments 中实现它，但我可能犯了一个错误？还是应该在 Activity 中实现它，例如保存现有片段的实例？

提前感谢那些愿意回答的人。 :)

Answer 1

非常粗略的想法

在创建 ??还是 oncreateview ？？？

   if(savedInstanceState == null){

        }else{

  int positionx = savedInstanceState.getInt("myposition"); //setfragment myposition ??!!??!!??
  myEdittext.setText(savedInstanceState.getString("myedittext")); //set text to edittext ??!!??!!??!!

    }

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
  super.onSaveInstanceState(savedInstanceState);
  // Save UI state changes to the savedInstanceState.
  // This bundle will be passed to onCreate if the process is
  // killed and restarted.

  savedInstanceState.putInt("myposition", position);
  savedInstanceState.putString("myedittext", myEdittext.getText().toString());

}


@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  // Restore UI state from the savedInstanceState.
  // This bundle has also been passed to onCreate.

  int positionx = savedInstanceState.getInt("myposition"); //setfragment myposition ??!!??!!??
  myEdittext.setText(savedInstanceState.getString("myedittext")); //set text to edittext ??!!??!!??!!

}