Android：通過刷卡而不是按鈕保存表格數據

Question

我對android非常陌生，這是我的第二個應用程序。我正在製作一個標籤式活動，其中第一個片段具有用於創建新任務的表單，第二個片段具有所有保存的任務的列表，第三個片段將在第二個列表中從列表中選擇時顯示任務上的評論分段。當我點擊第一個片段上的保存任務按鈕時，應用程序會正確保存該任務，並將其顯示在下一個片段中的任務列表中。但是，我不想在第一個片段中使用「保存任務」按鈕。我希望能夠在用戶從第一個活動滑動到第二個活動時立即保存任務。

爲此，我已嘗試從活動中的OnPageChangeListener.onPageScrolled()方法調用片段的saveTask()方法，但片段中的所有視圖都提供NullPointerException。如果我嘗試在活動的OnPageChangeListener.onPageScrollStateChanged()的保存任務按鈕上嘗試performClick()，則即使按鈕也會提供NullPointerException。當我打印到日誌以查看「保存任務」按鈕是否已初始化時，日誌會正確顯示按鈕ID。我不知道如何使用滑動將任務保存到數據庫。請幫忙！

這是我的主要活動：

public class AddTask extends AppCompatActivity { 

/** 
* The {@link PagerAdapter} that will provide 
* fragments for each of the sections. We use a 
* {@link FragmentPagerAdapter} derivative, which will keep every 
* loaded fragment in memory. If this becomes too memory intensive, it 
* may be best to switch to a 
* {@link FragmentStatePagerAdapter}. 
*/ 
private static SectionsPagerAdapter mSectionsPagerAdapter; 

/** 
* The {@link ViewPager} that will host the section contents. 
*/ 
private ViewPager mViewPager; 
public List<String> fragments = new Vector<String>(); 

/** 
* ATTENTION: This was auto-generated to implement the App Indexing API. 
* See https://g.co/AppIndexing/AndroidStudio for more information. 
*/ 
private GoogleApiClient client; 

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

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 
    // Create the adapter that will return a fragment for each of the three 
    // primary sections of the activity. 
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 

    //fill the fragments list with the fragment classes 
    fragments.add(AddTaskFragment.class.getName()); 
    fragments.add(TasksFragment.class.getName()); 
    fragments.add(CommentsFragment.class.getName()); 

    // Set up the ViewPager with the sections adapter. 
    mViewPager = (ViewPager) findViewById(R.id.container); 
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 
    mViewPager.setAdapter(mSectionsPagerAdapter); 
    mViewPager.setOffscreenPageLimit(2); 
    mViewPager.setCurrentItem(1); 

    final AddTaskFragment addTaskFrag = (AddTaskFragment) mSectionsPagerAdapter.getItem(0); 
    mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() { 
     @Override 
     public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { 
      android.support.v7.app.ActionBar actionBar = getSupportActionBar(); 
      switch (position) { 
       case 0: 
        actionBar.setTitle("Add New Task"); 
        break; 
       case 1: 
        actionBar.setTitle("Existing Tasks"); 
        break; 
       case 2: 
        actionBar.setTitle("Comments"); 
        break; 
      } 
     } 

     @Override 
     public void onPageSelected(int position) { 
      if (fragments.get(position).equals(TasksFragment.class.getName())) { 

      } 
     } 

     @Override 
     public void onPageScrollStateChanged(int state) { 
      if(mViewPager.getCurrentItem()==0) { 
       if (state == ViewPager.SCROLL_STATE_DRAGGING) { 
        if (addTaskFrag != null) { 
         addTaskFrag.saveTaskBtn.performClick(); 
        } 
       } 
      } 
     } 
    }); 
    // ATTENTION: This was auto-generated to implement the App Indexing API. 
    // See https://g.co/AppIndexing/AndroidStudio for more information. 
    client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build(); 
} 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_add_task, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 

@Override 
public void onStart() { 
    super.onStart(); 

    // ATTENTION: This was auto-generated to implement the App Indexing API. 
    // See https://g.co/AppIndexing/AndroidStudio for more information. 
    client.connect(); 
    Action viewAction = Action.newAction(
      Action.TYPE_VIEW, // TODO: choose an action type. 
      "AddTask Page", // TODO: Define a title for the content shown. 
      // TODO: If you have web page content that matches this app activity's content, 
      // make sure this auto-generated web page URL is correct. 
      // Otherwise, set the URL to null. 
      Uri.parse("http://host/path"), 
      // TODO: Make sure this auto-generated app deep link URI is correct. 
      Uri.parse("android-app://com.example.ishita.assigntasks/http/host/path") 
    ); 
    AppIndex.AppIndexApi.start(client, viewAction); 
} 

@Override 
public void onStop() { 
    super.onStop(); 
    // ATTENTION: This was auto-generated to implement the App Indexing API. 
    // See https://g.co/AppIndexing/AndroidStudio for more information. 
    Action viewAction = Action.newAction(
      Action.TYPE_VIEW, // TODO: choose an action type. 
      "AddTask Page", // TODO: Define a title for the content shown. 
      // TODO: If you have web page content that matches this app activity's content, 
      // make sure this auto-generated web page URL is correct. 
      // Otherwise, set the URL to null. 
      Uri.parse("http://host/path"), 
      // TODO: Make sure this auto-generated app deep link URI is correct. 
      Uri.parse("android-app://com.example.ishita.assigntasks/http/host/path") 
    ); 
    AppIndex.AppIndexApi.end(client, viewAction); 
    client.disconnect(); 
} 

/** 
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to 
* one of the sections/tabs/pages. 
*/ 
public class SectionsPagerAdapter extends FragmentPagerAdapter { 

    public List<String> fragmentsA; 

    public SectionsPagerAdapter(FragmentManager fm) { 
     super(fm); 
     fragmentsA = fragments; 
    } 

    @Override 
    public Fragment getItem(int position) { 
     //Instantiate the fragment at the position where the pager is. 
     return Fragment.instantiate(getApplicationContext(), fragmentsA.get(position)); 

    } 


    @Override 
    public int getCount() { 
     // return how many fragments there are in the tabbed activity 
     return fragmentsA.size(); 
    } 

    @Override 
    public int getItemPosition(Object object) { 
     return POSITION_NONE; 
    } 


    @Override 
    public CharSequence getPageTitle(int position) { 
     switch (position) { 
      case 0: 
       return "Add Task"; 
      case 1: 
       return "Tasks List"; 
      case 2: 
       return "Comments"; 
     } 
     return null; 
    } 
    } 
} 

這裏是我的片段形式的Java創建一個新的類：

/** 
* A placeholder fragment containing a simple view. 
*/ 
public class AddTaskFragment extends Fragment { 
/** 
* The fragment argument representing the section number for this 
* fragment. 
*/ 
final int PICK_CONTACT = 1; 

private static final String ARG_SECTION_NUMBER = "section_number"; 

public String mAssigneeName; 
public String mAssigneeContact; 
public String mTaskName; 
public String mDueDate; 
public String mComments = null; 

public AddTaskFragment() { 
} 

EditText dueDate; 
EditText assignee; 
EditText taskDescription; 
EditText comments; 
Button saveTaskBtn; 
View rootView; 
Calendar myCalendar = Calendar.getInstance(); 

DatePickerDialog.OnDateSetListener date = new DatePickerDialog.OnDateSetListener() { 

    @Override 
    public void onDateSet(DatePicker view, int year, int monthOfYear, 
          int dayOfMonth) { 
     // TODO Auto-generated method stub 
     myCalendar.set(Calendar.YEAR, year); 
     myCalendar.set(Calendar.MONTH, monthOfYear); 
     myCalendar.set(Calendar.DAY_OF_MONTH, dayOfMonth); 
     updateLabel(); 
    } 

}; 

private void updateLabel() { 

    String displayFormat = "MMM dd, yyyy"; //setting the format in which the date will be displayed 
    SimpleDateFormat sdf = new SimpleDateFormat(displayFormat, Locale.US); 

    dueDate.setText(sdf.format(myCalendar.getTime())); 
} 

/** 
* Returns a new instance of this fragment for the given section 
* number. 
*/ 
public static AddTaskFragment newInstance(int sectionNumber) { 
    AddTaskFragment fragment = new AddTaskFragment(); 
    Bundle args = new Bundle(); 
    args.putInt(ARG_SECTION_NUMBER, sectionNumber); 
    fragment.setArguments(args); 
    return fragment; 
} 



@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    rootView = inflater.inflate(R.layout.fragment_add_task, container, false); 

    dueDate = (EditText) rootView.findViewById(R.id.due_date); 
    taskDescription = (EditText) rootView.findViewById(R.id.description); 
    comments = (EditText) rootView.findViewById(R.id.comments); 
    assignee = (EditText) rootView.findViewById(R.id.assignee); 

    dueDate.setOnClickListener(new View.OnClickListener() { 

            @Override 
            public void onClick(View v) { 
             new DatePickerDialog(getActivity(), date, myCalendar 
               .get(Calendar.YEAR), myCalendar.get(Calendar.MONTH), 
               myCalendar.get(Calendar.DAY_OF_MONTH)).show(); 
            } 
           } 

    ); 

    assignee.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      try { 
       Intent intent = new Intent(Intent.ACTION_PICK); 
       intent.setType(ContactsContract.CommonDataKinds.Phone.CONTENT_TYPE); 
       startActivityForResult(intent, PICK_CONTACT); 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 
    }); 

    saveTaskBtn = (Button) rootView.findViewById(R.id.save_task); 
    Log.v("AddTaskFragment", "saveTaskBtn assigned to " + R.id.save_task); 
    saveTaskBtn.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      saveTask(); 
     } 
    }); 

    return rootView; 
} 

public void saveTask(){ 
    try { 
     mTaskName = taskDescription.getText().toString(); 
     taskDescription.setText(""); 
     mDueDate = dueDate.getText().toString(); 
     dueDate.setText(""); 
     mComments = comments.getText().toString(); 
     comments.setText(""); 
     assignee.setText(R.string.assignee_prompt); 
     if (mTaskName == null || mDueDate == null || mAssigneeName == null) { 
      Toast.makeText(getContext(), "Fields cannot be empty. Please fill some values.", Toast.LENGTH_SHORT).show(); 
     } else { 
      UpdateTask updateDB = new UpdateTask(); 
      updateDB.execute(); 
      Toast.makeText(getContext(), "Task saved.", Toast.LENGTH_SHORT).show(); 
     } 
    } catch (Exception e) { 
     e.printStackTrace(); 
    } 
} 

public void onActivityResult(int reqCode, int resultCode, Intent data) { 
    super.onActivityResult(reqCode, resultCode, data); 
    EditText assignee = (EditText) getActivity().findViewById(R.id.assignee); 
    switch (reqCode) { 
     case (PICK_CONTACT): 
      if (resultCode == Activity.RESULT_OK) { 
       Uri contactData = data.getData(); 
       Cursor cursor = getContext().getContentResolver().query(contactData, new String[]{ContactsContract.CommonDataKinds.Phone._ID, ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME, ContactsContract.CommonDataKinds.Phone.NUMBER}, null, null, null); 

       if (cursor.moveToFirst()) { 
        mAssigneeName = cursor.getString(cursor.getColumnIndexOrThrow(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME)); 
        mAssigneeContact = cursor.getString(cursor.getColumnIndexOrThrow(ContactsContract.CommonDataKinds.Phone.NUMBER)); 
        assignee.setText(mAssigneeName); 
        Toast.makeText(getActivity(), mAssigneeName + " has number " + mAssigneeContact, Toast.LENGTH_LONG).show(); 
       } 
       cursor.close(); 
      } 
      break; 
    } 

} 

public class UpdateTask extends AsyncTask<Void, Void, Void> { 

    protected Void doInBackground(Void... params) { 
     ContentValues taskDetails = new ContentValues(); 
     taskDetails.put(TasksContract.TaskEntry.COL_DESCRIPTION, mTaskName); 
     taskDetails.put(TasksContract.TaskEntry.COL_ASSIGNEE_KEY, mAssigneeContact); 
     taskDetails.put(TasksContract.TaskEntry.COL_CREATOR_KEY, "creatorID"); 
     taskDetails.put(TasksContract.TaskEntry.COL_DUE_DATE, mDueDate); 
     taskDetails.put(TasksContract.TaskEntry.COL_COMMENTS, mComments); 

     getContext().getContentResolver().insert(TasksContract.TaskEntry.CONTENT_URI, taskDetails); 

     Cursor cursor = getContext().getContentResolver().query(
       TasksContract.ProfileEntry.CONTENT_URI, 
       new String[]{TasksContract.ProfileEntry._ID}, 
       TasksContract.ProfileEntry.COL_CONTACT + "=?", 
       new String[]{mAssigneeContact}, 
       null 
     ); 
     if (!cursor.moveToFirst()) { 
      ContentValues contactDetails = new ContentValues(); 
      contactDetails.put(TasksContract.ProfileEntry.COL_NAME, mAssigneeName); 
      contactDetails.put(TasksContract.ProfileEntry.COL_CONTACT, mAssigneeContact); 

      getContext().getContentResolver().insert(TasksContract.ProfileEntry.CONTENT_URI, contactDetails); 
     } 
     cursor.close(); 
     return null; 
    } 
    } 

} 

這裏是碎片的XML：

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 

<LinearLayout 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:orientation="vertical" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="com.example.ishita.assigntasks.AddTaskFragment"> 

    <EditText 
     android:id="@+id/description" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_margin="10dp" 
     android:hint="@string/task_prompt" /> 

    <EditText 
     android:id="@+id/assignee" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_margin="10dp" 
     android:ems="10" 
     android:focusable="false" 
     android:inputType="textPersonName" 
     android:text="@string/assignee_prompt" /> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_margin="10dp" 
     android:orientation="horizontal"> 

     <TextView 
      android:id="@+id/date" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_weight="1" 
      android:text="@string/due_date" 
      android:textSize="18sp" /> 

     <EditText 
      android:id="@+id/due_date" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_weight="2" 
      android:ems="10" 
      android:focusable="false" 
      android:inputType="date" /> 

    </LinearLayout> 

    <EditText 
     android:id="@+id/comments" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_margin="10dp" 
     android:hint="@string/comments" 
     android:minHeight="?android:listPreferredItemHeight" /> 

    <Button 
     android:id="@+id/save_task" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center_horizontal" 
     android:text="@string/save_task" /> 


</LinearLayout> 
</ScrollView> 

LogCat：

02-18 13:48:05.538 3752-3752/? I/art: Late-enabling -Xcheck:jni 
02-18 13:48:05.628 3752-3752/com.example.ishita.assigntasks W/ResourceType: Found multiple library tables, ignoring... 
02-18 13:48:05.664 3752-3752/com.example.ishita.assigntasks I/GMPM: App measurement is starting up, version: 8487 
02-18 13:48:05.664 3752-3752/com.example.ishita.assigntasks I/GMPM: To enable debug logging run: adb shell setprop log.tag.GMPM VERBOSE 
02-18 13:48:05.823 3752-3788/com.example.ishita.assigntasks D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true 
02-18 13:48:05.840 3752-3752/com.example.ishita.assigntasks D/Atlas: Validating map... 
02-18 13:48:06.039 3752-3788/com.example.ishita.assigntasks I/Adreno-EGL: <qeglDrvAPI_eglInitialize:410>: EGL 1.4 QUALCOMM build: AU_LINUX_ANDROID_LA.BF.1.1.1_RB1.05.01.00.042.030_msm8974_LA.BF.1.1.1_RB1__release_AU() 
                     OpenGL ES Shader Compiler Version: E031.25.03.06 
                     Build Date: 05/17/15 Sun 
                     Local Branch: mybranch10089422 
                     Remote Branch: quic/LA.BF.1.1.1_rb1.22 
                     Local Patches: NONE 
                     Reconstruct Branch: AU_LINUX_ANDROID_LA.BF.1.1.1_RB1.05.01.00.042.030 + 6151be1 + NOTHING 
02-18 13:48:06.053 3752-3788/com.example.ishita.assigntasks I/OpenGLRenderer: Initialized EGL, version 1.4 
02-18 13:48:06.077 3752-3788/com.example.ishita.assigntasks D/OpenGLRenderer: Enabling debug mode 0 
02-18 13:48:06.123 3752-3752/com.example.ishita.assigntasks W/View: requestLayout() improperly called by android.widget.TextView{5fbdde1 V.ED.... ......ID 48,43-403,124} during layout: running second layout pass 
02-18 13:48:06.440 3752-3752/com.example.ishita.assigntasks V/case:msgCount:getInt: 0 
02-18 13:48:06.440 3752-3752/com.example.ishita.assigntasks V/getViewId: 2131493003 
02-18 13:48:06.485 3752-3752/com.example.ishita.assigntasks I/Timeline: Timeline: Activity_idle id: android.os.BinderProxy@9dab03c time:19983548 
02-18 13:48:10.458 3752-3752/com.example.ishita.assigntasks E/InputEventReceiver: Exception dispatching input event. 
02-18 13:48:10.458 3752-3752/com.example.ishita.assigntasks D/AndroidRuntime: Shutting down VM 
02-18 13:48:10.532 3752-3752/com.example.ishita.assigntasks E/AndroidRuntime: FATAL EXCEPTION: main 
                      Process: com.example.ishita.assigntasks, PID: 3752 
                      java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.widget.Button.performClick()' on a null object reference 
                       at com.example.ishita.assigntasks.AddTask$1.onPageScrollStateChanged(AddTask.java:100) 
                       at android.support.v4.view.ViewPager.dispatchOnScrollStateChanged(ViewPager.java:1811) 
                       at android.support.v4.view.ViewPager.setScrollState(ViewPager.java:404) 
                       at android.support.v4.view.ViewPager.onInterceptTouchEvent(ViewPager.java:1935) 
                       at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1961) 
                       at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) 
                       at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) 
                       at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) 
                       at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) 
                       at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) 
                       at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) 
                       at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) 
                       at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) 
                       at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) 
                       at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) 
                       at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) 
                       at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) 
                       at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2372) 
                       at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1722) 
                       at android.app.Activity.dispatchTouchEvent(Activity.java:2742) 
                       at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60) 
                       at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60) 
                       at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2333) 
                       at android.view.View.dispatchPointerEvent(View.java:8742) 
                       at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4136) 
                       at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4002) 
                       at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557) 
                       at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3610) 
                       at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3576) 
                       at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3693) 
                       at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3584) 
                       at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3750) 
                       at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557) 
                       at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3610) 
                       at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3576) 
                       at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3584) 
                       at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557) 
                       at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5823) 
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5797) 
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5768) 
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5913) 
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) 
at android.view.InputEventReceiver.nativeConsumeBatchedInputEvents(Native Method) 
at android.view.InputEventReceiver.consumeBatchedInputEvents(InputEventReceiver.java:176) 
at android.view.ViewRootImpl.doConsumeBatchedInput(ViewRootImpl.java:5884) 
at android.view.ViewRootImpl$ConsumeBatchedInputRunnable.run(ViewRootImpl.java:5936) 
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) 
at android.view.Choreographer.doCallbacks(Choreographer.java:580) 
at android.view.Choreographer.doFrame(Choreographer.java:548) 

Answer 1

您的OnPageChangeListener中頁面更改（當選擇另一個頁面時）的調用方法是onPageSelected。

另外，在您的PagerAdapter上調用getItem實例化新的片段。爲了解決這個問題，你需要在你的PagerAdapter中保存你的碎片列表，並創建一個方法來檢索它們。

//in PagerAdapter: 
private List<Fragment> fragmentList; 

public SectionsPagerAdapter(FragmentManager fm) { 
    super(fm); 
    fragmentsA = fragments; 
    fragmentList = new ArrayList<Fragment>(); 

    for(int i = 0; i < 3; i++){ 
     fragmentList.add(Fragment.instantiate(getApplicationContext(), fragmentsA.get(i));); 
    } 
} 

public Fragment getFragment(int position){ 

    return fragmentList.get(position); 
}