將ArrayList對象傳遞給片段

Question

我很難解決這個問題。我試圖從可展開的列表視圖點擊發送3個不同的自定義對象數組列表。下面是擴展列表視圖代碼（我只包括了第一集團的地位和兒童，但在現實中有更多）：

*/ 
public class MyWorkout extends BaseActivity{ 

ExpandableListView expandableListView; 
HashMap<String, List<String>> Workouts_details; 
List<String> Workout_list; 
WorkoutsAdapter mAdapter; 

@Override 
protected void onCreate(@Nullable Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.my_workout); 
    mToolBar = activateToolbar(); 
    setUpNavigationDrawer(); 


    expandableListView = (ExpandableListView) findViewById(R.id.listViewWorkouts); 
    Workouts_details = DataProvider.getInfo(); 
    Workout_list = new ArrayList<>(Workouts_details.keySet()); 
    mAdapter = new WorkoutsAdapter(this, Workouts_details, Workout_list); 



    expandableListView.setAdapter(mAdapter); 

    expandableListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() { 
     @Override 
     public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) { 
      if (groupPosition == 0) { 
       if (childPosition == 0) { 
        Intent intent = new Intent(getApplicationContext(), WorkoutDaysActivity.class); 
        intent.putExtra("workout", "w29w1"); 
        startActivity(intent); 
       } 
       if (childPosition == 1) { 
        Intent intent = new Intent(getApplicationContext(), WorkoutDaysActivity.class); 
        intent.putExtra("workout", "w29w1"); 
        startActivity(intent); 
       } 

在那裏，每個childClick發送應用WorkoutDaysActivity，其中3個選項卡設置與片段。這裏是這個類的代碼：

public class WorkoutDaysActivity extends BaseActivity{ 

@Override 
protected void onCreate(@Nullable Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.workout_days); 
    mToolBar = activateToolbar(); 
    setUpNavigationDrawer(); 


    ViewPager vp = (ViewPager) findViewById(R.id.view_pager); 
    this.addPages(vp); 

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout); 
//  tabLayout.setTabGravity(TabLayout.GRAVITY_FILL); 
    tabLayout.setupWithViewPager(vp); 
    tabLayout.setOnTabSelectedListener(listener(vp)); 

} 

//ADD ALL PAGES 
private void addPages(ViewPager pager) { 
    MyFragPagerAdapter adapter = new MyFragPagerAdapter(getSupportFragmentManager()); 
    Intent intent = getIntent(); 
    String workout = intent.getStringExtra("workout"); 
    Bundle args = new Bundle(); 
    args.putString("workout", workout); 

    MondayFragment mondayFragment = new MondayFragment(); 
    mondayFragment.setArguments(args); 
    adapter.addPage(mondayFragment); 
    WedFragment wedFragment = new WedFragment(); 
    wedFragment.setArguments(args); 
    adapter.addPage(wedFragment); 
    FridayFragment fridayFragment = new FridayFragment(); 
    fridayFragment.setArguments(args); 
    adapter.addPage(fridayFragment); 
    pager.setAdapter(adapter); 
} 

private TabLayout.OnTabSelectedListener listener(final ViewPager pager) { 
    return new TabLayout.OnTabSelectedListener() { 
     @Override 
     public void onTabSelected(TabLayout.Tab tab) { 
      pager.setCurrentItem(tab.getPosition()); 
     } 

     @Override 
     public void onTabUnselected(TabLayout.Tab tab) { 

     } 

     @Override 
     public void onTabReselected(TabLayout.Tab tab) { 

     } 
    }; 
} 
} 

然後從那裏，我有3個選項卡片段類。每個類看起來像這樣：

public class WedFragment extends Fragment { 

Bundle args = getArguments(); 
String workout3 = args.getString("workout"); 

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.wed_fragment, null); 

//  //RECYCLERVIEW 
    RecyclerView rv = (RecyclerView) view.findViewById(R.id.mRecyclerWed); 
    rv.setLayoutManager(new LinearLayoutManager(this.getActivity())); 
    rv.setAdapter(new MyRecyclerAdapter(this.getActivity(), getWedWorkout())); 

    return view; 


} 

private ArrayList<Workout> getWedWorkout() { 
    //COLLECTION OF MONDAY WORKOUT 

    ArrayList<Workout> workout = new ArrayList<>(); 
    switch(workout3) { 
     case "w29w1" : { 
      Workout workouts = new Workout("Bench", "60", "6", "155", false); 

      //ADD TO COLLECTION 
      workout.add(workouts); 

      workouts = new Workout("Bench", "70", "5", "175", false); 
      workout.add(workouts); 

      break;} 
     case "w29w2" :{ 
      Workout workouts = new Workout("Squat", "60", "6", "155", false); 

      //ADD TO COLLECTION 
      workout.add(workouts); 

      workouts = new Workout("Squat", "70", "5", "175", false); 
      workout.add(workouts); 

     break;} 
    } return workout; 



    //SINGLE EXERCISE 


} 

@Override 
public String toString() { 
    return "Wednesday"; 
} 
} 

編輯：我編輯了我的帖子，這就是爲什麼我試圖做。在我看來，它應該起作用，但事實上並非如此。當應用程序試圖打開片段和崩潰我得到這個錯誤：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bestworkouts.sheikoworkout/com.bestworkouts.sheikoworkout.WorkoutDaysActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference 
                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3254) 
                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350) 
                       at android.app.ActivityThread.access$1100(ActivityThread.java:222) 
                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795) 
                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                       at android.os.Looper.loop(Looper.java:158) 
                       at android.app.ActivityThread.main(ActivityThread.java:7229) 
                       at java.lang.reflect.Method.invoke(Native Method) 
                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
                      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference 
                       at com.bestworkouts.sheikoworkout.Fragments.WedFragment.<init>(WedFragment.java:24) 
                       at com.bestworkouts.sheikoworkout.WorkoutDaysActivity.addPages(WorkoutDaysActivity.java:47) 
                       at com.bestworkouts.sheikoworkout.WorkoutDaysActivity.onCreate(WorkoutDaysActivity.java:27) 
                       at android.app.Activity.performCreate(Activity.java:6876) 
                       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135) 
                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207) 
                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)  
                       at android.app.ActivityThread.access$1100(ActivityThread.java:222)  

Answer 1

這是不清楚的地方在你的代碼正試圖將ArrayList對象發送到Fragment - 但我的建議是，你讓你的類（Workout）到延長Parcelable，然後發送ArrayList<Workout> - 你可以使用Bundle類的putParcelableArrayList(String key, ArrayList<? extends Parcelable> value)方法簽名，然後設置Bundle作爲fragment.setArguments(Bundle)方法的參數。從本質上講，你會有這樣的代碼：

ArrayList<Workout> workoutList = new ArrayList<Workout>(); 
workoutList.add(<some-workout-object>) 
Bundle bundle = new Bundle(); 
bundle.putParcelableArrayList("mondayWorkoutList", workoutList); 
Fragment fragment = new MondayFragment(); 
fragment.setArguments(bundle); 

看那Fragment tutorial關於如何參數發送到使用捆綁片段的例子。您可能還想看看API documentation for Bundle class

我希望這能夠讓我們有所瞭解。