How can I create all the fragments of viewpager2 when the app runs?-CodePudding

My MainActivity contains viewpager2.

And the viewpager2 manages 4 fragments(HomeFragment, DictionaryFragment, UploadFragment, CommunityFragment).

My ViewPagerAdapter:

inner class ViewPagerAdapter(activity: FragmentActivity) : FragmentStateAdapter(activity) {
        private val fragments: List<Fragment> =
            listOf(HomeFragment(), DictionaryFragment(), UploadFragment(), CommunityFragment())
        private var viewList = arrayOf(
            layoutInflater.inflate(R.layout.fragment_home, null),
            layoutInflater.inflate(R.layout.fragment_dictionary, null),
            layoutInflater.inflate(R.layout.fragment_upload, null),
            layoutInflater.inflate(R.layout.fragment_community, null),
        )

        override fun getItemCount() = viewList.size

        override fun createFragment(position: Int): Fragment = fragments[position]
    }

I want to execute the function of the Dictionary fragment in the main activity.

So I tried supportFragmentManager.findFragmentByTag("f1") as DictionaryFragment).myFunction().

However, this code throws a NullPointerException.

My guess is that it's because the Dictionary fragment hasn't been created yet.

How can I create all the fragments of viewpager2 when the app runs?

CodePudding user response：

At First, convert the type of list to the array list

private val fragments: ArrayList<Fragment>

Then you can add the fragment to the list

fun addFragment(Fragment fragment){
    fragments.add(fragment);
}

the viewpager2 automatically manages the adding and removeing of the fragments

CodePudding user response：

Set off screen limit to the number of fragments you want to create on viewpager.

mViewPager.setOffscreenPageLimit(n); // number of fragments you want to create