Android – Determine when a ViewPager changes pages

androidandroid-viewpagerandroid-widget

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?

Best Answer

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.
    }
});

Related Solutions

Android – ViewPager PagerAdapter not updating the View

There are several ways to achieve this.

The first option is easier, but bit more inefficient.

Override getItemPosition in your PagerAdapter like this:

public int getItemPosition(Object object) {
    return POSITION_NONE;
}

This way, when you call notifyDataSetChanged(), the view pager will remove all views and reload them all. As so the reload effect is obtained.

The second option, suggested by Alvaro Luis Bustamante (previously alvarolb), is to setTag() method in instantiateItem() when instantiating a new view. Then instead of using notifyDataSetChanged(), you can use findViewWithTag() to find the view you want to update.

The second approach is very flexible and high performant. Kudos to alvarolb for the original research.

Android – IllegalStateException: Can not perform this action after onSaveInstanceState with ViewPager

Please check my answer here. Basically I just had to :

@Override
protected void onSaveInstanceState(Bundle outState) {
    //No call for super(). Bug on API Level > 11.
}

Don't make the call to super() on the saveInstanceState method. This was messing things up...

This is a known bug in the support package.

If you need to save the instance and add something to your outState Bundle you can use the following:

@Override
protected void onSaveInstanceState(Bundle outState) {
    outState.putString("WORKAROUND_FOR_BUG_19917_KEY", "WORKAROUND_FOR_BUG_19917_VALUE");
    super.onSaveInstanceState(outState);
}

In the end the proper solution was (as seen in the comments) to use :

transaction.commitAllowingStateLoss();

when adding or performing the FragmentTransaction that was causing the Exception.

Best Answer

Related Solutions

Android – ViewPager PagerAdapter not updating the View

Android – IllegalStateException: Can not perform this action after onSaveInstanceState with ViewPager

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