Android Viewpager saving data and views

问题

Hopefully someone can help me with a slight problem/confusion I have with Viewpagers and saving data.

PROBLEM:

When scrolling across the four views I have, the first view has two spinners, two textviews that display a string or a selected item. if I scroll on to the third page and back to the second page, the data in the first view is lost. hense needing to save the data.

Would this be done in the two routines stated below? (best guess is it would be) if so, what sort of commands need to be stated?

CODE:

@Override   
public void restoreState(Parcelable arg0, ClassLoader arg1) {       
}

@Override
public Parcelable saveState() {
    return null;
}

EXTRA INFO: the viewpager is being used in

public Object instantiateItem(View collection, int position) {
}

The complete list of methods are as follows:

@Override
public void destroyItem(View arg0, int arg1, Object arg2) {
    ((ViewPager) arg0).removeView((View) arg2);
}

@Override
public boolean isViewFromObject(View arg0, Object arg1) {
    return arg0 == ((View) arg1);
}

@Override
public Parcelable saveState() {
    return null;
}

@Override
public void finishUpdate(View arg0) {
}

@Override
public void restoreState(Parcelable arg0, ClassLoader arg1) {
}

@Override
public void startUpdate(View arg0) {
}

回答1:

Instead of saving the state of those pages you could modify your ViewPager so it buffers all of your pages instead of destroying them and recreating them when you scroll.

So for example if you have 4 pages:

ViewPager pager = (ViewPager) findViewById(R.id.viewpager);
pager.setOffscreenPageLimit(3); // the number of "off screen" pages to keep loaded each side of the current page
pager.setAdapter(new PageAdapter(context));

Now your pages will be kept 'alive'

Be careful with this technique however because it will increase memory consumption. The number passed to setOffscreenPageLimit() is the number of pages each side of the current page to retain. In this case we have 4 pages in total so the worst case scenario is when we are at the far edge of of the page set - we have the currently visible page and then the remaining 3 pages are off screen to one side and are thus kept in memory. However, with a larger data set it could potentially mean 7 pages are kept in memory (current page plus 3 either side).

Generally the more optimal solution would be to properly deal with unloading and reloading the page state and re-render them.

Hope this helps

来源：https://stackoverflow.com/questions/8891968/android-viewpager-saving-data-and-views

标签

android

save

instantiation

android-viewpager