Android:通过更改片段更改菜单项的可见性 [英] Android: Changing visibility on menu items with changing fragment

问题描述

每当我更改活动中的片段时，我都想更改片段活动 (abs) 菜单项的可见性.这些片段是 SherlockListFragments.

I want to change the visibility of menu items of a fragment activity (abs) when ever I change the fragment in the activity. The fragments are SherlockListFragments.

我想显示/隐藏的菜单项是我在创建菜单时创建的微调器:

The menu items I want to show/hide are spinners I create on menu creation:

public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    MenuInflater inflater = getSupportMenuInflater();

    IcsSpinner herbSortSpinner = new IcsSpinner(this, null, R.attr.actionDropDownStyle);
    SpinnerAdapter herbSortSpinnerAdapter = ArrayAdapter.createFromResource(this, R.array.herb_sort_elements, android.R.layout.simple_spinner_dropdown_item);
    herbSortSpinner.setAdapter(herbSortSpinnerAdapter);
    herbSortSpinner.setOnItemSelectedListener(this);
    herbSortSpinner.setId(HERB_SPINNER_ID);
    menu.add(R.string.menu_sort).setActionView(herbSortSpinner).setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);

    IcsSpinner noteSortSpinner = new IcsSpinner(this,  null, R.attr.actionDropDownStyle);
    SpinnerAdapter noteSortSpinnerAdapter = ArrayAdapter.createFromResource(this, R.array.note_sort_elements, android.R.layout.simple_spinner_dropdown_item);
    noteSortSpinner.setAdapter(noteSortSpinnerAdapter);
    noteSortSpinner.setOnItemSelectedListener(this);
    noteSortSpinner.setId(NOTE_SPINNER_ID);
    menu.add(R.string.menu_sort).setActionView(noteSortSpinner).setVisible(false).setEnabled(false).setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);

    inflater.inflate(R.menu.activity_lexicon, menu);
    menuHolder.setMenu(menu);
    return true;
}

我切换片段的逻辑是:

public boolean onNavigationItemSelected(int position, long itemId) {

    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    switch(position) {
    case 0:
        List<Herb> herbList = findHerbsByIntent(getHerbLocale());
        HerbListFragment herbListFragment = new HerbListFragment();
        herbListFragment.setListAdapter(new HerbListAdapter(this, getHerbLocale(), herbList));
        fragmentTransaction.replace(R.id.fragment_container, herbListFragment, HERB_LIST_FRAGMENT_TAG);
        //menuHolder.showHerbsSpinner();
        break;
    case 1:
        SymptomListFragment symptomListFragment = new SymptomListFragment();
        symptomListFragment.setListAdapter(new SymptomListAdapter(this, getDefaultSymptomLocale()));
        fragmentTransaction.replace(R.id.fragment_container, symptomListFragment, SYMPTOM_LIST_FRAGMENT_TAG);
        //menuHolder.showHerbsSpinner();
        break;
    case 2:
        NoteRepository noteRepository = new NoteRepository(this);
        List<Note> notes = noteRepository.getNoticables(ReferedType.HERB);
        NoteListFragment noteListFragment = new NoteListFragment();
        noteListFragment.setListAdapter(new NoteListAdapter(this, getHerbLocale(), notes));
        fragmentTransaction.replace(R.id.fragment_container, noteListFragment, NOTE_LIST_FRAGMENT_TAG);
        //menuHolder.showNotesSpinner();
        break;
    case 3:
        FavoriteRepository favoriteRepository = new FavoriteRepository(this);
        Set<Integer> favoriteHerbs = favoriteRepository.getFavorables(ReferedType.HERB);
        List<Herb> favoriteHerbList = herbRepository.getHerbsByIds(favoriteHerbs, getHerbLocale());
        FavoriteHerbListFragment favoriteHerbListFragment = new FavoriteHerbListFragment();
        favoriteHerbListFragment.setListAdapter(new HerbListAdapter(this, getHerbLocale(), favoriteHerbList));
        fragmentTransaction.replace(R.id.fragment_container, favoriteHerbListFragment, HERB_LIST_FRAGMENT_TAG);
        //menuHolder.showHerbsSpinner();
        break;
    }
    fragmentTransaction.commit();

    return true;
}

我的第一个想法是将菜单对象保存在一个 holder 类中，并在我切换片段时在那里操作它(在上面的每个 case 语句中).

My first idea was to hold the menu object in a holder class and manipulate it there whenever I switch the fragment (in every case statement above).

static class MenuHolder {

    private Menu mMenu;

    void setMenu(Menu menu) {
        mMenu = menu;
    }

    void showNotesSpinner() {
        if (mMenu != null) {
            mMenu.findItem(HERB_SPINNER_ID).setVisible(false).setEnabled(false);
            mMenu.findItem(NOTE_SPINNER_ID).setVisible(true).setEnabled(true);
        }
    }

    void showHerbsSpinner() {
        if (mMenu != null) {
            mMenu.findItem(NOTE_SPINNER_ID).setVisible(false).setEnabled(false);            
            mMenu.findItem(HERB_SPINNER_ID).setVisible(true).setEnabled(true);
        }
    }
}

我的问题是没有给定 ID 的菜单项是活动本地常量.我在这里得到了一个 NPE.有谁知道我该如何解决这个问题?有没有更好的方法来更改切换片段时的菜单?

My problem is that there is no menu item with the given ID which are activity local constants. I get an NPE here. Does anybody have an idea how I can fix that? Is there a better way to change the menu on switching fragments?

最好的问候卡斯腾

推荐答案

是否有更好的方法来更改切换片段时的菜单?

Is there a better way to change the menu on switching fragments?

可能是:).

• 在您的片段 onCreate 中，添加:

setHasOptionsMenu (true);

文档:

报告此片段希望通过接收对 onCreateOptionsMenu(Menu, MenuInflater) 和相关方法的调用来参与填充选项菜单.

Report that this fragment would like to participate in populating the options menu by receiving a call to onCreateOptionsMenu(Menu, MenuInflater) and related methods.

• 覆盖onPrepareOptionMenu 片段类中的方法.
• Override onPrepareOptionMenu method in your fragment class.

准备要显示的屏幕的标准选项菜单.这在菜单显示之前调用，每次显示.您可以使用此方法有效地启用/禁用项目或以其他方式动态修改内容.

Prepare the Screen's standard options menu to be displayed. This is called right before the menu is shown, every time it is shown. You can use this method to efficiently enable/disable items or otherwise dynamically modify the contents.

然后，在此方法中，尝试通过 ID 查找您的菜单项，并使它们可见/不可见、启用/禁用，如下所示:

Then, in this method, try to find your menu items by ID, and make them visible/unvisible, enabled/disabled, like this :

@Override
public void onPrepareOptionsMenu(Menu menu) {    
    menu.findItem(HERB_SPINNER_ID).setVisible(false).setEnabled(false);
}

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