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Question

I am able to show Fragments as tabs using ViewPager .

What I want to achieve is,

1. The contents of a fragment should be loaded only when it is selected as the current tab.
2. Once a tab is shown and is loaded, then whenever I come back to the same tab then it is retained, ie not loaded again.

I know to retain all tabs I can use the following,

viewPager.setOffscreenPageLimit(4); // 4 is total number of tabs

But when I do this, it loads all 4 tabs at the very beginning ie calls onCreateView of all 4 tabs in the beginning. How can I make it load only when it is shown for the first time and then retain for later use.

PS This functionality exists in Twitter and Facebook Android apps.

Answer 1

To retain the fragments make your view pager adapter extend FragmentPagerAdapter instead of FragmentStatePagerAdapter. The fragments will be retained in memory, so there is no need to set the page limit. To fire the things you have to load upon user visibility, just extend setUserVisibleHint as mentioned above.

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (isVisibleToUser && myData == null) {
        loadData()
    }
}

Answer 2

The android fragments do provide below method

@Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
    }

This method gets called in when the fragments become visible on screen only. So whatever the code you are executing in onCreateView() can be managed in this method.