如何处理片段内的网络呼叫 [英] How to handle network calls inside a Fragment

问题描述

我有以下情况:

我有一个托管了 ViewPager 的 Activity ，并且我有4个 Fragments ;

I have an Activity that hosts a ViewPager, and I have 4 Fragments;

开头的 ViewPager 包含片段A ，

当用户在 ViewPager 片段B 上滑动时，进入 ViewPager ，然后依次是 Fragment C 和片段D ...等等...

when the user swipes on the ViewPager Fragment B goes into the ViewPager, then Fragment C and Fragment D ...etc...

现在，实例化 FragmentPagerAdapter 时，至少会创建至少两个Fragments.

Now as soon as the FragmentPagerAdapter is instantiated at least 2 of the Fragments are created.

这带来了2个问题:

1. 每个 Fragment 都需要执行网络呼叫，但是我不想做不必要的呼叫(如果用户从不刷卡到Fragment，我不想对Fragment B进行网络呼叫.B )；
2. 类似于1.)，当一个Fragment执行网络调用时，我需要显示一个 ProgessDialog ，但是如果用户从未去过它，我不想显示来自Fragment B的对话框...

1. Every Fragment needs to perform network calls, but I do not want to do unnecessary ones (I do not want to make network calls for Fragment B, if the user never swipes to Fragment B );
2. similar to 1.), I need to show a ProgessDialog when a Fragment perform network calls, but I do not want to show dialogs from Fragment B if the user never goes to it...

在这种情况下，我应该使用哪种模式?

Please what kind of pattern should I use in such a circumstance?

活动

public class PagerActivity extends ActionBarActivity {

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.viewpager_layout);

ViewPager pager=(ViewPager)findViewById(R.id.pager);
TabPageIndicator tabs=(TabPageIndicator)findViewById(R.id.titles);

pager.setAdapter(buildAdapter());
tabs.setViewPager(pager);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
}

FragmentPagerAdapter

public class MyFragmentPagerAdapter extends FragmentPagerAdapter {


@Override
public int getCount() {
    return (4);
}

@Override
public Fragment getItem(int position) {


    if (position == 1) {
        if (dashbardFragment == null)
            dashbardFragment = DashBoardFragment.newInstance(position);
        return dashbardFragment;
    }
    if (position == 0) {
        if (listOfParticipantFragment == null)
            listOfParticipantFragment = ListOfParicipantsFragment
            .newInstance(position);
        return listOfParticipantFragment;
    }

}

1个片段

public class ListOfParicipantsFragment extends Fragment {

public static ListOfParicipantsFragment newInstance(int position) {
    ListOfParicipantsFragment frag = new ListOfParicipantsFragment();
    return (frag);
}

public static String getTitle(Context ctxt, int position) {
    return myApplication.getContext().getResources().getString(R.string.list_of_participants_fragment_title);
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View result = inflater.inflate(R.layout.guest_list_fragment_layout,
            container, false);

    return (result);
}

推荐答案

在下面的每个 fragment override 方法中尝试此操作，并在可见时调用函数:

Try this, in each fragment override below method and call your function when it is visible:

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if(isVisible()){
        if(isVisibleToUser){
            Log.d("MyTag","My Fragment is visible");
        }else{
            Log.d("MyTag","My Fragment is not visible");
        }
    }
}

编辑

注意:仅当使用 FragmentPagerAdapter 或 FragmentStatePagerAdapter

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