setCurrentItem（）上ViewPager

Question

我創建這樣的自定義視圖尋呼機：

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}

和主要片段使用：

 mPagerAdapter = new TaskPagerAdapter(getFragmentManager()); 
    mViewPager.setAdapter(mPagerAdapter); 
    mViewPager.setCurrentItem(-2); 

在 setCurrentItem我不得不

哪個數字要使用，直到我沒有得到一個nullpoiner錯誤？我想NotificationFragment（）類是第一個開始查看頁面

編輯

絲毫mViewPager.setCurrentItem（-1）;我有打擊錯誤：

Process: safarayaneh.com.anotify.debug, PID: 21484 
                      java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.Fragment.setMenuVisibility(boolean)' on a null object reference 
                       at android.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:120) 
                       at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:1034) 
                       at android.support.v4.view.ViewPager.populate(ViewPager.java:1248) 
                       at android.support.v4.view.ViewPager.populate(ViewPager.java:1116) 
                       at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1642) 
                       at android.view.View.measure(View.java:18788) 
                       at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:1028)... 

Answer 1

讀setCurrentItem

Set the currently selected page. If the ViewPager has already been through its first layout with its current adapter there will be a smooth animated transition between the current item and the specified item.

問題

mViewPager.setCurrentItem(-1); 

不要設置-1 or -2。 索引從0開始。

編輯

switch (position) { 
    case 0: 
     fragment = new NotificationFragment(); 
     break; 
    case 1: 
     break; 
    case 2: 
     break; 
    case 3: 
     break; 
    case 4: 
     break; 

} 
return fragment; 

爲什麼1,2,3,4 BLANK。你應該

switch (position) { 
    case 0: 
     fragment = new NotificationFragment(); 
     break; 

} 
return fragment; 

mViewPager.setCurrentItem（0）嘗試;

Answer 2

由於NotificationFragment有第一個位置。 它的指數是0

因此，應該像mViewPager.setCurrentItem(0);