Android我如何有一个ViewPager，其中页数由ASyncTask确定

Question

I have an activity which has a ViewPager on it. I would like to have one page in the pager for every item returned from a server call using an AsyncTask.

My server call is a paginated call, so the first time i call the server i ask for items 1 through 10. I then want my ViewPager to have a page for each of these 10 items and i can swipe left and right through the pages. When i swipe to the 10th page, i want to call the server to get the next 10 pages (ie pages 11 through 20) so that on the 10th page i can swipe to get to page 11.

I see a lot of examples online for how i can use an AsyncTask to get the contents of a single " ViewPager page's fragment ", but this is not what i want, I want the AsyncTask to determine the " number of pages in the pager " (by returning a list of data objects containing information to display on each page).

This is simple with lists and ListAdapters, but i can not work out how to do this with ViewPagers and PagerAdapters.

Any help would be greatly appreciated.

Answer 1

I appear to have got this working in a very basic state.

DataManager I have a DataManager which is responsible for getting the items from the server using a ASyncTask

• it contains a list of the items returned from the server
• it contains the ASyncTask that goes to the server to get the items, when the task completes the list of items is updated
• it contains a "getSize()" method to return the size of the list of items
• it has a "getItem(int position)" method which returns the item at the given position
• it has an "isItemAvailble(int position)" method, if the item at the given index is not in the list of items, the task is called again to get the next batch of items
• it has a DataSetObservable so that the manager can inform any observers when its data changes (ie when a task has completed and its items updated)

PagerAdapter

The PagerAdapter is as follows

class MyPageAdapter extends FragmentPagerAdapter {

    // Members
    ....
    private DataManager dataManager;

    // create an observer to listen for changes in the data manager
    private final DataSetObserver observer = new DataSetObserver() {
        @Override
        public void onChanged() {
            Toast.makeText(appCtx(), "MyPagerAdapter observer's onChanged called", Toast.LENGTH_LONG).show();
            // Notify observers on this adapter that item list has changed.
            notifyDataSetChanged();
        }

    };

    // constructor
    public MyPageAdapter(DataManager dataManager, .....) {
        super(fm);
        this.dataManager = dataManager;
        dataManager.registerDataSetObserver(observer);
    }

    /**
     * Get the number of items from the manager
     */
    private int getSize() {
        return dataManager.size();
    }

    // get the item for the given position
    @Override
    public Fragment getItem(int position) {
        // if the next item is not available the managers task will get the next batch
        dataManager.ensureItemAvailable(position+1);

        // get this position's item from the data manager and create a fragment using that item
        Object obj = dataManager.getItem();
        return MyPagerFragment.newInstance(obj);
    }
....
....
}