参考以下
answer,我试图实现我目前在项目中所做的事情,即使用以下代码:
@Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
因为当前的实现,我的ViewPager中的所有页面都被重新加载.我在第一时间实现这个原因的原因是重新加载一个片段(根据用户输入是动态的).
阅读完参考后,我对我应该做的事情有了一个模糊的想法,我覆盖了instantiateItem()方法,但在我尝试setTag()时,我对如何实现它感到困惑.我确实尝试了以下内容:
@Override
public Object instantiateItem(ViewGroup viewgroup, int position) {
// TODO Auto-generated method stub
View viewA = viewgroup.getChildAt(0);
viewA.setTag("FragmentA");
View viewB = viewgroup.getChildAt(1);
viewB.setTag("FragmentB");
View viewC = viewgroup.getChildAt(2);
viewC.setTag("FragmentC");
return super.instantiateItem(viewgroup, position);
}
在我的界面实现中,我调用了以下内容:
PlayingFragment fragment = new PlayingFragment();
fragment.setArguments(element);
getSupportFragmentManager().beginTransaction().add(fragment,"NowPlaying").commit();
adapter.notifyDataSetChanged();
pager.findViewWithTag("FragmentC");
当前的实现给了我一个NullPointerException
at:viewA.setTag(“FragmentA”);
有人可以帮我实现这个setTag()和findViewWithTag()实现吗?
最佳答案 当您调用viewA.setTag(“FragmentA”)时,视图组尚未初始化.这是此异常的直接原因.
要避免此问题,您需要在设置viewGroup后设置标记,即,您已经夸大了视图布局或创建了片段.
例如,FragmentStatePagerAdapter的instantiateItem的默认代码如下.
@Override
public Object instantiateItem(ViewGroup container, int position) {
// If we already have this item instantiated, there is nothing
// to do. This can happen when we are restoring the entire pager
// from its saved state, where the fragment manager has already
// taken care of restoring the fragments we previously had instantiated.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);
if (f != null) {
return f;
}
}
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
Fragment fragment = getItem(position);
if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
if (mSavedState.size() > position) {
Fragment.SavedState fss = mSavedState.get(position);
if (fss != null) {
fragment.setInitialSavedState(fss);
}
}
while (mFragments.size() <= position) {
mFragments.add(null);
}
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
mFragments.set(position, fragment);
mCurTransaction.add(container.getId(), fragment);
return fragment;
}
您可以在创建片段/视图时在getItem方法中设置标记.