PagerAdapter start position

Question

I'm using the following example to impliment my viewPager: http://code.google.com/p/viewpagerexample/issues/list

The problem with this example is that I can't figure out how to set my starting position, the default starting position is 0. Basically I wan't to be able to control if there is an available view on its left or the right.

Is there any way to control center's View current position? is there a better way to do it? is it possible to make it circular?

Gunnysack

check this https://mcmap.net/q/262879/-align-the-child-views-in-center-of-the-viewpager-android – Essayistic

Answer 1

I've found a way to set it's position, which is done outside of the class:

 awesomePager = (ViewPager) findViewById(R.id.awesomepager);
 awesomePager.setAdapter(awesomeAdapter);
 awesomePager.setCurrentItem(CurrentPosition);

and it can be limited by calculating the amount of items I want to fit in to it

Gunnysack

note that if awesomeAdapter is backed by a Cursor/LoaderManager you'll need to be careful about when setCurrentItem is called to avoid stealing focus (too late) or failing to move the page at all (too early) - see this – Mortification

did not work for me because my other fragments are not ready at that point and I've got an exception since my app tried to use a variable from the currentPosition fragment that was not created yet – Cavalryman

Working Perfect. Setting view pager when fragment is ready works fine, tried this when fragment is ready and you have currentposition available. Thanks @Kirill – Bostwick

Is there any way to start ViewPager from the end? I mean like in RecyclerView, when you set up new LinearLayoutManager(..., inverse=true) . What I want is: ViewPager jump immidiately to the last item, without fire up fragments in the middle – Pone

@Pone it's pretty late, but in case someone has the same issue, passing false wouldn't show the user the transition that happens: viewPager.setCurrentItem(newPosition, false); – Propaedeutic

I think the issue here is that the pager will start a position zero, then page to "CurrentPosition" thus instantiating fragments which don't need instantiation. – Kriemhild

Answer 2

I have noticed that if you recreate Activity (orientation change) with ViewPager having FragmentStatePagerAdapter, then the Adapter will reuse it's Fragments. The way to stop it is:

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    if (viewPager != null) {
        // before screen rotation it's better to detach pagerAdapter from the ViewPager, so
        // pagerAdapter can remove all old fragments, so they're not reused after rotation.
        viewPager.setAdapter(null);
    }
    super.onSaveInstanceState(savedInstanceState);
}

but then after Activity recreation ViewPager alwayes opens page 0 first and setCurrentItem(CurrentPosition); doesn't work. Fix for that is changing page after delay:

new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        viewPager.setCurrentItem(newPosition);
    }
}, 100);

Eyeful

The delay is indeed needed after a recreate() call! :) – Confiture

Answer 3

To start with the last fragment I did this:

PagerAdapter pagerAdapter = new PagerAdapter();
viewPager.setAdapter(pagerAdapter);
viewPager.setCurrentItem(pagerAdapter.getCount() - 1);

Yaekoyael

Answer 4

I came across a problem whereby if I set the current item before I set the adapter, the first item I get back will always be the one at position 0.

Make sure you do:

awesomePager.setAdapter(awesomeAdapter);
awesomePager.setCurrentItem(CurrentPosition);

and not:

awesomePager.setCurrentItem(CurrentPosition);
awesomePager.setAdapter(awesomeAdapter);

Christychristye

Answer 5

I have an array of size more than 1000 and in dymanic viewpager I was facing leftswipe stuck on firstload. The below code solved this and resulted in smooth scroll:

@Override
onResume(){
   super.onResume();
   viewPager.setCurrentItem(newPosition);
}

Overview

Answer 6

I'm using 3 fragments and on starting my app, the second (middle) fragment will be shown by default. Just I'm using the onResume function and all works great.

@Override
protected void onResume() {
    super.onResume();
    m_viewPager.setCurrentItem(1);
}

Jerrold

Worked for me as opposed to using a timer in onCreate. Thanks! – Pastorship

did not work for me because my 2nd fragment is not ready at that point and I've got an exception since my app tried to use a variable from the 2nd fragment that was not created yet – Cavalryman

So how you could use a variable that not even created ?! – Jerrold

Answer 7

Using viewPager.setCurrentItem(newPosition); shows to the user the transition from the starting page to the newPosition, to prevent that from happening and show the newPosition directly as if it was the starting point, I added false to the second parameter something like this:

int newPosition = pages.size()-1; // Get last page position

viewPager.setCurrentItem(newPosition, false); // 2nd parameter (false) stands for "smoothScroll"

Propaedeutic

Answer 8

I encountered same problem. When I initialize ViewPager, the indicator position was 0. This may depends on amount of calculating for Pager contents. I use ViewTreeObserver like below.

mGlobalLayoutListener = new ViewTreeObserver.OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        mViewPager.setCurrentItem(newPosition);
        removeOnGlobalLayoutListener(mSlidingTabLayout.getViewTreeObserver(), mGlobalLayoutListener);
    }
};
mSlidingLayout.getViewTreeObserver().addOnGlobalLayoutListener(mGlobalLayoutListener);

and,

private void removeOnGlobalLayoutListener(ViewTreeObserver observer, ViewTreeObserver.OnGlobalLayoutListener listener) {
       if (observer == null) return;
       if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) {
               observer.removeGlobalOnLayoutListener(listener);
       } else {
               observer.removeOnGlobalLayoutListener(listener);
       }
} 

In this way, also never to bother with time setting of delay.

Silverstein

Answer 9

@Override
public Object instantiateItem(ViewGroup container, int position) {
    View currentPage = null;
    switch(position){
        case 0:
            currentPage = LayoutInflater.from(context).inflate(R.layout.page0, null)    
            break;
        case 1:
            currentPage = LayoutInflater.from(context).inflate(R.layout.page1, null)    
            ///////////// This page will be default ////////////////////
            ((ViewPager)container).setCurrentItem(position);
            ////////////////////////////////////////////////////////////
            break;
        case 2:
            currentPage = LayoutInflater.from(context).inflate(R.layout.page2, null)    
            break;
    return currentPage;
}

Jetsam