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android – Determine when a ViewPager changes pages

Posted by: admin March 11, 2020 Leave a comment

Questions:

I have three pages (Fragments) inside a ViewPager, however I only want to display a menu item for two of those pages.

The code given in a previous SO answer does not seem to work:

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

    if (isVisibleToUser == true) { }
    else if (isVisibleToUser == false) {  }

}

Eclipse says @Override isn’t needed and super can’t be set. It’s never called by the system, and even if it was how would I determine which page was being shown at the moment? Could I have some help here?

How to&Answers:

Use the ViewPager.onPageChangeListener:

viewPager.addOnPageChangeListener(new OnPageChangeListener() {
    public void onPageScrollStateChanged(int state) {}
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}

    public void onPageSelected(int position) {
        // Check if this is the page you want.
    }
});

Answer:

ViewPager.setOnPageChangeListener is deprecated now. You now need to use ViewPager.addOnPageChangeListener instead.

for example,

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

Answer:

You can also use ViewPager.SimpleOnPageChangeListener instead of ViewPager.OnPageChangeListener and override only those methods you want to use.

viewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {

    // optional 
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { }

    // optional 
    @Override
    public void onPageSelected(int position) { }

    // optional 
    @Override
    public void onPageScrollStateChanged(int state) { }
});

Hope this help 🙂

Edit:
As per android APIs, setOnPageChangeListener (ViewPager.OnPageChangeListener listener) is deprecated. Please check this url:- Android ViewPager API

Answer:

For Kotlin,

view_pager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {

            override fun onPageScrollStateChanged(state: Int) {
            }

            override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {

            }

            override fun onPageSelected(position: Int) {
            }
        })

Answer:

For ViewPager2,

viewPager.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
  override fun onPageSelected(position: Int) {
    super.onPageSelected(position)
  }
})

where OnPageChangeCallback is a static class with three methods:

onPageScrolled(int position, float positionOffset, @Px int positionOffsetPixels),
onPageSelected(int position), 
onPageScrollStateChanged(@ScrollState int state)