PagerAdapter start position

问题

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?

回答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

回答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);

回答3:

To start with the last fragment I did this:

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

回答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);

回答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);
}

回答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);
}

回答7:

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.

回答8:

@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;
}

回答9:

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"

来源：https://stackoverflow.com/questions/11879315/pageradapter-start-position

标签

android

android-viewpager

swipe