在FragmentPagerAdapter片段正确交互 [英] Properly Interacting with fragments in FragmentPagerAdapter
问题描述
我使用的是FragmentPagerAdapter一个活动，第3页片段之间，除了ViewPager。根据从第一个分片输入（谷歌地图上的标记），我在做API请求当用户切换到片段2或3，然后更新这些片段的看法。
I'm using a FragmentPagerAdapter for an activity, to page between 3 fragments, in addition to a ViewPager. Based on input from the first fragment (markers on a google map), I'm making API requests when the user switches to fragment 2 or 3, and then updating those fragment views.
总的想法是，我管理的FragmentPagerAdapter内SparseArray，然后创建了一个viewPager onPageChangeListener：
The general idea is that I manage a SparseArray within the FragmentPagerAdapter, and then create an onPageChangeListener for the viewPager:
pager.setAdapter(pagerAdapter);
pager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
if (position == 1) {
SecondFragment fragment = (SecondFragment) pagerAdapter.getFragment(1);
fragment.update(currentMarker);
} else if (position == 2) {
ThirdFragment fragment = (ThirdFragment) pagerAdapter.getFragment(2);
fragment.update(currentMarker);
}
}
});
我也overrided的instantiateItem和destroyItem在FragmentPagerAdapter，正常删除的，在我的sparseArray重新添加片段的引用。
I also overrided the instantiateItem and destroyItem in the FragmentPagerAdapter, to properly remove and re-add fragment references in my sparseArray.
这工作pretty很好，但问题是，当我转动我的设备，当我第二次或第三片段页面上。这让我想呼吁片段的方法（在该活动的使用onPageSelected）当一个NullPointerException异常 - 我猜，因为活动是重建，那些片段尚未创建使用onPageSelected触发时
This works pretty well, but the issue is when I rotate my device when I'm on the second or third fragment page. It gives me a NullPointerException when trying to call a method on the fragment (in the activity's onPageSelected) - I'm guessing because the activity is recreated, those fragments haven't been created yet when onPageSelected triggers.
我在想，一个更好的方法可能是想出了一个办法让这些片段只是使API调用时，他们看到，而不是由活动触发它（这可能是清洁 - 少通信/从片段通常是更好），但是任何的建议是AP preciated。
I'm thinking that a better approach might be to come up with a way to have the fragments just make the API call when they're visible, instead of having the activity trigger it (which might be cleaner - less communication to/from fragments is typically better), but any advice would be appreciated.
推荐答案
ONSELECT（第2页）当你做API调用，让你的API调用的结果，应该有更新的API供的onSaveInstanceState引用的对象回调
OnSelect(page2 ) when you do the API calls and get your API call result , there should be a callback to update an object referenced by the API for 'OnSaveInstanceState'.
如果你这样做，那么IMO，这里是什么ü从框架中得到：
If you do that then IMO , here is what u get from the framework:
API返回结果。
结果更新片段
该片段被任何调用处理为'的onSaveInstanceState
results update a fragment that fragment gets processed by any call to 'OnSaveInstanceState'
OnOrientationChange ::与条件是发生之后的API返回结果
片段保存状态反映了API的结果。
OnOrientationChange :: with condition that it occurs AFTER the API returns results Fragment is saved with state reflecting the API results
活性是由于方向改变重建
在SavedInstanceState！= null，则重新实例片段，包括从早期的API调用的残留状况....
Activity is recreated due to Orientation change on SavedInstanceState != null it reinstantiates the fragment from the state including the residue of the earlier api call....
看到接受<一个href=\"http://stackoverflow.com/questions/6787071/android-fragment-how-to-save-states-of-views-in-a-fragment-when-another-fragmen\">answer这里更详细的内容。
see accepted answer here for additional detail
这篇关于在FragmentPagerAdapter片段正确交互的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
