getArguments 返回 null

Question

我需要将arraylist 从一个片段转移到另一个片段。我看了几篇有同样问题的文章，但没有一个选项不能解决我的问题....
来自 BakeFragment

OrderFragment orderFragment = new OrderFragment();
                   Bundle bundle = new Bundle();
                   bundle.putStringArrayList(ORDER_KEY, orderList);
                    orderFragment.setArguments(bundle);

我需要在 OrderFragment 中获取这个数组列表。我如何尝试做到这一点

第一版

Bundle mBundle = this.getArguments();
orderArrayList = mBundle.getStringArrayList(ORDER_KEY);

错误：

java.lang.NullPointerException
        at com.zhisheng.navdrawer.model.OrderFragment.onCreateView(OrderFragment.java:38)
        at android.app.Fragment.performCreateView(Fragment.java:1699)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:885)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
        at android.app.BackStackRecord.run(BackStackRecord.java:682)
        at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)
        at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441)
        at android.os.Handler.handleCallback(Handler.java:730)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5137)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:756)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:572)
        at miui.dexspy.DexspyInstaller.main(DexspyInstaller.java:171)
        at dalvik.system.NativeStart.main(Native Method)

第二版

if(getArguments()!=null){
        orderArrayList = this.getArguments().getStringArrayList("key");
    }

没有错误，但什么也没发生。

public class MainActivity extends AppCompatActivity {
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;

// nav drawer title
private CharSequence mDrawerTitle;

// used to store app title
private CharSequence mTitle;

// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mTitle = mDrawerTitle = getTitle();

    // load slide menu items
    navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

    // nav drawer icons from resources
    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

    navDrawerItems = new ArrayList<NavDrawerItem>();



    // adding nav drawer items to array
    // Home
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
    // Find People
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
    // Photos
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
    // Communities, Will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));
    // Pages
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
    // What's hot, We  will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[6], navMenuIcons.getResourceId(6, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[7], navMenuIcons.getResourceId(7, -1)));
    // Find People
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[8], navMenuIcons.getResourceId(8, -1)));
    // Photos
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[9], navMenuIcons.getResourceId(9, -1)));
    // Communities, Will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[10], navMenuIcons.getResourceId(10, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[11], navMenuIcons.getResourceId(11, -1)));


    // Recycle the typed array
    navMenuIcons.recycle();

    mDrawerList.setOnItemClickListener(new SlideMenuClickListener());

    // setting the nav drawer list adapter
    adapter = new NavDrawerListAdapter(getApplicationContext(),
            navDrawerItems);
    mDrawerList.setAdapter(adapter);

    // enabling action bar app icon and behaving it as toggle button
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setHomeButtonEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.navigation_drawer_open, R.string.navigation_drawer_close) {
        public void onDrawerClosed(View view) {
            getSupportActionBar().setTitle(mTitle);
            // calling onPrepareOptionsMenu() to show action bar icons
            invalidateOptionsMenu();

        }

        public void onDrawerOpened(View drawerView) {
            getSupportActionBar().setTitle(mDrawerTitle);
            // calling onPrepareOptionsMenu() to hide action bar icons
            invalidateOptionsMenu();
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    if (savedInstanceState == null) {


        displayView(11);
    }

}

/**
 * Slide menu item click listener
 */
private class SlideMenuClickListener implements
        ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
                            long id) {
        // display view for selected nav drawer item
        displayView(position);
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // toggle nav drawer on selecting action bar app icon/title
    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action bar actions click
    switch (item.getItemId()) {
        case R.id.action_settings:
          return true;
        default:
          displayView(11);

            //Toast.makeText(getApplicationContext(), "RasRas", Toast.LENGTH_LONG).show();
            return true;
    }
}

/* *
 * Called when invalidateOptionsMenu() is triggered
 */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    // if nav drawer is opened, hide the action items
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
    menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(menu);
}

/**
 * Diplaying fragment view for selected nav drawer list item
 */
private void displayView(int position) {
    // update the main content by replacing fragments
    Fragment fragment = null;
    switch (position) {
        case 0:
            fragment = new BakeFragment();
            break;
        case 1:
            fragment = new GarnishFragment();
            break;
        case 2:
            fragment = new HotDishesFragment();
            break;
        case 3:
            fragment = new DesertsFragment();
            break;
        case 4:
            fragment = new HomeFragment();
            break;
        case 5:
            fragment = new SnacksFragment();
            break;
        case 6:
            fragment = new DrinkFragment();
            break;
        case 7:
            fragment = new PizzaFragment();
            break;
        case 8:
            fragment = new SaladFragment();
            break;
        case 9:
            fragment = new ConfectionFragment();
            break;
        case 10:
            fragment = new SoupFragment();
            break;
        case 11:
            fragment = new OrderFragment();
        default:
            break;
    }

    if (fragment != null) {
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.frame_container, fragment).commit();

        // update selected item and title, then close the drawer
        mDrawerList.setItemChecked(position, true);
        mDrawerList.setSelection(position);
        setTitle(navMenuTitles[position]);
        mDrawerLayout.closeDrawer(mDrawerList);
    } else {
        // error in creating fragment
        Log.e("MainActivity", "Error in creating fragment");
    }
}

@Override
public void setTitle(CharSequence title) {
    mTitle = title;
    getSupportActionBar().setTitle(mTitle);
}

/**
 * When using the ActionBarDrawerToggle, you must call it during
 * onPostCreate() and onConfigurationChanged()...
 */

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    // Sync the toggle state after onRestoreInstanceState has occurred.
    mDrawerToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    // Pass any configuration change to the drawer toggls
    mDrawerToggle.onConfigurationChanged(newConfig);
}

烘焙片段

public class BakeFragment extends Fragment {

final static String ORDER_KEY="key";

String myString;

ListView listView;
ArrayList<MenuItem> arrayList;
CustomAdapter customAdapter;
MenuItem menuItem;

ArrayList<String>  orderList;

View rootView = null;


Integer[] quantity = {
  1, 2, 3, 4, 5, 6, 7, 8, 9, 10
};

String[] bakeList = new String[]{
        "Булочка с кунжутом", "Ватрушка с творогом", "Качори с чечевицей", "Лепешка \"Пападам\"",
        "Лепешка \"Паратха\"", "Лепешка \"Чапати\"", "Лепешка с сыром", "Пирожное \"Корзиночка\"",
        "Пирожок с капустой", "Пирожок с картофелем", "Пряник кокосовый экадашный" , "Самоса с вишней",
        "Самоса с клубникой", "Самоса с малиной","Самоса с овощами и паниром", "Самоса с сухофруктами (печеная)",  "Самоса с творогом", "Самоса с черной смородиной",
        "Самоса с яблоком в карамели"
};


Integer[] imagesOfBakeList = new Integer[]{
        R.drawable.bake1, R.drawable.bake2, R.drawable.bake3, R.drawable.bake4, R.drawable.bake5,
        R.drawable.bake6, R.drawable.bake7, R.drawable.bake8, R.drawable.bake9, R.drawable.bake10,
        R.drawable.bake11, R.drawable.bake12, R.drawable.bake13, R.drawable.bake14, R.drawable.bake15,
        R.drawable.bake16, R.drawable.bake17, R.drawable.bake18, R.drawable.bake19


};

String[] priceOfBakeList = new String[]{
        "30", "60", "60", "30", "70", "30", "70", "90", "60", "60", "60", "60", "60", "60", "60", "60",
        "60", "60", "60"
};



@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

     rootView = inflater.inflate(R.layout.list_item, container, false);

    listView = (ListView)rootView.findViewById(R.id.list_of_menu_item);
    orderList = new ArrayList<String>();
    arrayList = new ArrayList<MenuItem>();
    for(int i = 0; i < bakeList.length; i++) {
        menuItem = new MenuItem(imagesOfBakeList[i], bakeList[i], priceOfBakeList[i]);
        arrayList.add(menuItem);
    }
    customAdapter = new CustomAdapter(getActivity().getApplicationContext(), arrayList);
    listView.setAdapter(customAdapter);

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        View v = null;


        @Override
        public void onItemClick(AdapterView<?> parent, final View view, int position, long id) {
            //Toast.makeText(getActivity().getApplicationContext(), "Вы заказали " + customAdapter.getItem(position), Toast.LENGTH_SHORT).show();
            LayoutInflater layoutInflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = layoutInflater.inflate(R.layout.view, null);
            String dishForOrderList;
            final int s = customAdapter.getPrice(position);
            final String dish = customAdapter.getItem(position).toString();
            final String allstr;
            Spinner spinner = (Spinner) v.findViewById(R.id.spinView);
            final TextView orderText = (TextView) v.findViewById(R.id.order_text);
            ArrayAdapter<CharSequence> spinnerAdapter = ArrayAdapter.createFromResource(getActivity(), R.array.option, android.R.layout.simple_spinner_item);
            spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            spinner.setAdapter(spinnerAdapter);
            spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                @Override
                public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                    String selected = parent.getSelectedItem().toString();
                    int t = Integer.parseInt(selected);
                    myString = dish + " x" + t + "     " + (s * t);
                    String abc = dish+" x"+t+"     !";
                    orderText.setText(myString);
                     Toast.makeText(getActivity(), myString, Toast.LENGTH_LONG).show();

                }

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

                }
            });

            AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());


            builder.setView(v);
            builder.setTitle("Сколько порций " + dish + " вы хотите заказать?");
            builder.setCancelable(false);

            builder.setNegativeButton("Заказать", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {

                    orderList.add(myString);

                  Toast.makeText(getActivity(), orderList+"", Toast.LENGTH_LONG).show();
                   OrderFragment orderFragment = new OrderFragment();
                   Bundle bundle = new Bundle();
                   bundle.putStringArrayList(ORDER_KEY, orderList);
                    orderFragment.setArguments(bundle);
                    dialog.cancel();
                }
            });
            builder.setPositiveButton("Отмена", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    dialog.cancel();
                }
            });
            AlertDialog alertDialog = builder.create();
            alertDialog.show();

        }
    });

    return rootView;

}

}

订单片段

public class OrderFragment extends Fragment {

View rootView = null;
ListView orderListView;
ArrayList<String> orderArrayList;
ArrayAdapter<String> stringArrayAdapter;

final static String ORDER_KEY="key";


@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    rootView = inflater.inflate(R.layout.order_list, container, false);
    orderArrayList = new ArrayList<String>();

   Bundle mBundle = this.getArguments();
   orderArrayList = mBundle.getStringArrayList(ORDER_KEY);

 /*   if(getArguments()!=null){
        orderArrayList = this.getArguments().getStringArrayList("key");
    }*/
   // orderArrayList = this.getArguments()!=null? getArguments().getStringArrayList("array") : null;
    //Toast.makeText(getActivity(), "d = "+orderArrayList, Toast.LENGTH_LONG).show();
//        orderArrayList = bundle.getStringArrayList("key");
  orderListView = (ListView)rootView.findViewById(R.id.order_list_view);
    stringArrayAdapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, orderArrayList);
    orderListView.setAdapter(stringArrayAdapter);

    return rootView;
}}

Answer 1

我觉得你的问题可以追溯到这段代码：

public void onClick(DialogInterface dialog, int which) {

    orderList.add(myString);

    Toast.makeText(getActivity(), orderList+"", Toast.LENGTH_LONG).show();
    OrderFragment orderFragment = new OrderFragment();
    Bundle bundle = new Bundle();
    bundle.putStringArrayList(ORDER_KEY, orderList);
    orderFragment.setArguments(bundle);
    dialog.cancel();
}

由于单击了对话框按钮，您正试图创建一个 OrderFragment。但是，由于您没有将此实例附加到活动，因此永远不会设置参数。在 displayView() 方法中你有这个：

case 11:
    fragment = new OrderFragment();

基本上，您拥有的片段没有设置任何参数 - 这就是您之后看不到它们的原因。

为了解决这个问题，我建议您采取几个步骤：

1. 实现正确的片段 - 片段通信。请记住，片段不应该直接相互通信（除非它们是嵌套的，但这不是你的情况）。如果您通过活动组织它会更好 - BakeFragment 获取订单，将它们发送到活动，活动将它们设置为 OrderFragment 的参数。您可以在此处获得有关此方法的一个很好的示例和更多信息：http://developer.android.com/training/basics/fragments/communicating.html

2. 重新组织你的 displayView() 方法。目前，您将在每次调用此方法时强制创建所需片段的新实例。这可能会导致不良行为 - 性能不佳、返回堆栈的奇怪状态等。此外，当片段重新创建时，您将无法从片段参数的自动保存中受益。我建议您使用标签并首先检查您要显示的片段是否已经存在。

   FragmentManager fm = getSupportFragmentManager();
   Fragment fragment = fm.findByTag(THE_FRAGMENT_TAG);
   if (fragment == null) {
       // logic to create a fragment instance
   } 
   // logic to show the fragment
   

Answer 2

我唯一一次看到您在 FragmentTransaction 中使用的 OrderFragment 是在您的 MainActivity displayView 方法中创建它时。在那里，它没有设置任何参数。

您的 BakeFragment 确实创建了一个 OrderFragment 并设置了它的参数，但它永远不会通过 FragmentTransaction 添加，并且一旦您的 onClick(DialogInterface dialog, int which) 方法执行完毕，它就会超出范围。因此，从不使用带有参数集的 OrderFragment。

您的意思是通过使用 FragmentTransaction 向用户显示此片段吗？如果是这样，您可以让 BakeFragment 定义一个带有方法的接口，该方法向侦听器指示用户决定创建订单或取消订单。让 MainActivity 实现此接口并将自己注册为 BakeFragment 上的侦听器。

PS：为什么您的 AlertDialog 否定和肯定按钮单击处理程序似乎颠倒了您的逻辑？