FragmentStatePagerAdapter onPageSelected事件 [英] FragmentStatePagerAdapter onPageSelected event

问题描述

我有6个片段内FragmentStatePagerAdapter。

I have a FragmentStatePagerAdapter with 6 fragments inside.

每个片段连接的服务器并加载数据。

Each Fragment connect's to the server and loads data.

现在，服务器连接被在Fragment.onStart（），这意味着，在任何时刻，我有3 http请求正在进行（所选片段，和一个每边一个）。

Right now, the server connection is being done in Fragment.onStart(), that means that at any moment, I have 3 http requests going (the selected Fragment, and one to each side).

我要的是有当时只有一个连接，所以我想用

What I want is to have only one connection at the time, so I figure to use

 viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener()
 { 
    @Override
    public void onPageSelected(final int position)
    {
        CustomFragment fragment = (CustomFragment) myFragmentStatePagerAdapter.getItem(position);

        fragment.onSelected();//do stuff in here
    }
 });

的事情是，的getItem（）返回片段的新实例，没有添加到管理器（因此，尚未视图中创建，等等）。

The thing is, getItem() returns a new instance of the fragment, not yet added to the manager (and thus, not yet view created, etc).

另外，我已经试过 setUserVisibleHint（布尔isVisibleToUser），但不是随叫随到可见，只有在isVisibleToUser = FALSE

Also, I've tried setUserVisibleHint(boolean isVisibleToUser) but is not being call on visible, only on isVisibleToUser = false

那么，如何实现onPageSelected（）事件的片段？

So, how to achieve a "onPageSelected()" event for the Fragment?

在此先感谢

推荐答案

你将覆盖最好的解决办法 setUserVisibleHint（）。请确保您延长 FragmentPagerAdapter 。从它的<一个href="https://github.com/android/platform_frameworks_support/blob/master/v4/java/android/support/v4/app/FragmentPagerAdapter.java"相对=nofollow>来源$ C ​​$ C 你可以看到它调用 setUserVisibleHint（真）可见的碎片了。我用它所有的时间和它工作得很好。

The best solution for you would be to override setUserVisibleHint(). Make sure you extend FragmentPagerAdapter. From its source code you can see it calls setUserVisibleHint(true) for visible fragments too. I use it all the time and it works well.

// adapter
public static class PlayerAdapter extends FragmentStatePagerAdapter {
    public PlayerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return 6;
    }

    @Override
    public Fragment getItem(int position) {
        return new SimpleFragment();
    }
}

// fragment
public class SimpleFragment extends Fragment {

    private static final String TAG = BookControlsFragment.class.getSimpleName();

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_simple, container, false);
    }

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        Log.d(TAG, "setUserVisibleHint: " + isVisibleToUser);
    }
}

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