为什么我不能从FragmentPagerAdapter中分离片段？

Question

我想从我的FragmentPagerAdapter分离一个片段，但它似乎没有工作。这里是我pageradapter类，这是我从原代码复制：

public class PagerAdapter1 extends FragmentPagerAdapter { 

    private List<String> fragments; 
     private static final String TAG = "FragmentPagerAdapter"; 
     private static final boolean DEBUG = true; 
     private Fragment mCurrentPrimaryItem = null; 
     private final FragmentManager mFragmentManager; 
     private FragmentTransaction mCurTransaction = null; 

    /** 
    * @param fm 
    * @param fragments2 
    */ 
    public PagerAdapter1(FragmentManager fm, List<String> fragments2) { 
     super(fm); 
     mFragmentManager=fm; 
     this.fragments = fragments2; 
    } 
    /* (non-Javadoc) 
    * @see android.support.v4.app.FragmentPagerAdapter#getItem(int) 
    */ 
    @Override 
    public Fragment getItem(int position) { 
     //return this.fragments.get(position); 
     return Fragment.instantiate(ViewPagerActivity.context, fragments.get(position)); 

    } 

    /* (non-Javadoc) 
    * @see android.support.v4.view.PagerAdapter#getCount() 
    */ 
    @Override 
    public int getCount() { 
     return this.fragments.size(); 
    } 



     /** 
    * Return the Fragment associated with a specified position. 
    */ 


    @Override 
    public void startUpdate(ViewGroup container) { 
    } 

    @Override 
    public Object instantiateItem(ViewGroup container, int position) { 
     Log.i("asasd", "asdasdasdasdasd"); 

     if (mCurTransaction == null) { 
      mCurTransaction = mFragmentManager.beginTransaction(); 
     } 

     final long itemId = getItemId(position); 

     // Do we already have this fragment? 
     String name = makeFragmentName(container.getId(), itemId); 

     Fragment fragment = mFragmentManager.findFragmentByTag(name); 
     if (fragment != null) { 
      if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment); 
       mCurTransaction.attach(fragment); 

     } else { 

      fragment = getItem(position); 
      if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment); 
      mCurTransaction.add(container.getId(), fragment, 
        makeFragmentName(container.getId(), itemId)); 
      // Log.i("asdJANIANI", " " + getFragmentTag(container.getId(),0)); 
      //Log.i("JANI", " " + getItem(0)); 
     } 

     if (fragment != mCurrentPrimaryItem) { 
      fragment.setMenuVisibility(false); 
      fragment.setUserVisibleHint(false); 
     } 
     **destroyItem(container,0,getItem(0));** 

     return fragment; 
    } 

    @Override 
    public void destroyItem(ViewGroup container, int position, Object object) { 
     if (mCurTransaction == null) { 
      mCurTransaction = mFragmentManager.beginTransaction(); 
     } 
     if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object 
       + " v=" + ((Fragment)object).getView()); 
     mCurTransaction.detach((Fragment)object); 
    } 

    @Override 
    public void setPrimaryItem(ViewGroup container, int position, Object object) { 
     Fragment fragment = (Fragment)object; 
     if (fragment != mCurrentPrimaryItem) { 
      if (mCurrentPrimaryItem != null) { 
       mCurrentPrimaryItem.setMenuVisibility(false); 
       mCurrentPrimaryItem.setUserVisibleHint(false); 
      } 
      if (fragment != null) { 
       fragment.setMenuVisibility(true); 
       fragment.setUserVisibleHint(true); 
      } 
      mCurrentPrimaryItem = fragment; 
     } 

     if (position == 0){ 
      this.notifyDataSetChanged(); 
     } 

    } 

    @Override 
    public void finishUpdate(ViewGroup container) { 
     if (mCurTransaction != null) { 
      mCurTransaction.commitAllowingStateLoss(); 
      mCurTransaction = null; 
      mFragmentManager.executePendingTransactions(); 
     } 
    } 

    @Override 
    public boolean isViewFromObject(View view, Object object) { 
     return ((Fragment)object).getView() == view; 
    } 

    @Override 
    public Parcelable saveState() { 
     return null; 
    } 

    @Override 
    public void restoreState(Parcelable state, ClassLoader loader) { 
    } 

    /** 
    * Return a unique identifier for the item at the given position. 
    * 
    * <p>The default implementation returns the given position. 
    * Subclasses should override this method if the positions of items can change.</p> 
    * 
    * @param position Position within this adapter 
    * @return Unique identifier for the item at position 
    */ 
    public long getItemId(int position) { 
     return position; 
    } 

    private static String makeFragmentName(int viewId, long id) { 
     return "android:switcher:" + viewId + ":" + id; 
    } 


} 

我改变的只有一件事，我在instantiateItem（）方法实现的destroyItem()方法，因为我要分离的片段（位置0）每次我实例化一个片段。我没有得到任何错误，它只是没有得到分离。为什么？

预先感谢您！

Answer 1

这让我连续忙了两天。我终于找到了答案在这里：

Update ViewPager dynamically?

基本上不使用FragmentPagerAdapter，但使用FragmentStatePagerAdapter并覆盖getItemPosition（）方法。事实证明，前者不允许对其数据源进行适当的更改，并且不会反映它们。

这个该死的bug花费了我大量的时间:(但上面的链接帮助我解决它以分钟为单位。

Answer 2

在FragmentPagerAdapter.java源，

82 @Override
83 publicObject instantiateItem(ViewGroup container, int position) {
84  if (mCurTransaction == null) {
85   mCurTransaction = mFragmentManager. beginTransaction();
86  }
88  // Do we already have this fragment?
89  String name = makeFragmentName (container. getId(), position);
90  Fragment fragment = mFragmentManager. findFragmentByTag (name);
91  if (fragment != null) {
92   if (DEBUG) Log. v (TAG, "Attaching item #" + position + ": f=" + fragment);
93   mCurTransaction. attach (fragment);
94  } else {
95   fragment = getItem (position);
96   if (DEBUG) Log. v (TAG, "Adding item #" + position + ": f=" + fragment);
97   mCurTransaction. add (container. getId(), fragment,
98     makeFragmentName (container. getId(), position));
99  }
100  if (fragment != mCurrentPrimaryItem) {
101   fragment. setMenuVisibility (false);
102   fragment. setUserVisibleHint (false);
103  }
105  return fragment;
106 }
108 @Override
109 publicvoid destroyItem(ViewGroup container, int position, Object object) {
110  if (mCurTransaction == null) {
111   mCurTransaction = mFragmentManager. beginTransaction();
112  }
113  if (DEBUG) Log. v (TAG, "Detaching item #" + position + ": f=" + object
114    + " v=" + ((Fragment)object). getView());
115  mCurTransaction. detach ((Fragment)object);
116 }

你可以看到它使用附加/分离显示/隐藏片段，这就是为什么他们不工作