java - 无法在屏幕旋转时保留菜单项

Question

我在 .onCreateOptionsMenu 中创建了一个菜单项 (Spinner)，并希望在屏幕旋转时保留选择。我知道使用 SharedPreferences 是常见的做法，但是在这种情况下我有点困惑，因为我没有在 .onCreate() 中创建 View ，而我通常会在其中创建 View 加载我保存的首选项:

    @Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.action_bar_spinner, menu);
    MenuItem item = menu.findItem(R.id.spinner);
    mSpinner = (Spinner) item.getActionView();
    int selectedPosition = mPrefs.getInt(SPINNER_SELECTION, 0);
    mSpinner.setSelection(selectedPosition);
    if (isOnline()) {
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getApplicationContext(), R.array.spiner_list_item_array, R.layout.custom_spinner);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        mSpinner.setAdapter(adapter);
        mSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                mPrefsEditor.putInt(SPINNER_SELECTION, i);
                mPrefsEditor.commit();
                switch (i) {
                    case 0:
                        mBaseURL = "https://api.themoviedb.org/3/movie/popular/";
                        calltoRetrofit(mBaseURL);
                        break;
                    case 1:
                        mBaseURL = "https://api.themoviedb.org/3/movie/top_rated/";
                        calltoRetrofit(mBaseURL);
                        break;
                    case 2:
                        mIsFavoriteSelected = true;
                        mMovieURLS.clear();
                        retrieveMovies();
                        break;

                    default:
                        mBaseURL = "https://api.themoviedb.org/3/movie/popular/";
                        break;
                }


            }

            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {

            }
        });
        return true;
    } else {
        return true;
    }
}

编辑:

当我尝试设置 GridLayoutManager 的方向时，我现在收到一个空指针:

 if (savedInstanceState != null){
                glm = savedInstanceState.getParcelable(SPINNER_SELECTION);
            }
            glm.setOrientation(LinearLayoutManager.VERTICAL);

Answer 1

首先，在 onCreate 之外的其他方法中访问 SharedPreferences 是完全有效的。如果您在使用此帖子时遇到问题，请提供错误消息/问题。

其次，为了在屏幕旋转时保留内容，您可以在 Activity 中使用 onSaveInstanceState 来保存微调器选择并在屏幕旋转时在 onCreate 中获取状态.例如:

private int saved_selection = -1

@Override
protected void onCreate(Bundle savedInstanceState) {
    //...

    if (savedInstanceState != null) {
        saved_selection = savedInstanceState.getInt("SPINNER_SELECTION");
    }

    //...
}

@Override
public void onSaveInstanceState(Bundle outState) {
    outState.putInt("SPINNER_SELECTION", saved_selection);

    // call superclass to save any view hierarchy
    super.onSaveInstanceState(outState);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    //...
    // set `saved_selection = i;`  in your adapter
    //...
    if( saved_selection >= 0 ) {
        mSpinner.setSelection(saved_selection);
    }
}