PagerAdapter，当所有页面实例化时，Xamarin Android

Question

I have this class for PagerAdapter :

public class MyPagerAdapter : PagerAdapter
{
    private List<string> tab_names = new List<string>();
    int[] page = { Resource.Layout.page0, Resource.Layout.page1, Resource.Layout.page2, Resource.Layout.page3, Resource.Layout.page4 };
    public Action OnAllPagesAdded = delegate { };

    public override Java.Lang.Object InstantiateItem(ViewGroup container, int page_offset)
    {
        var view = LayoutInflater.From(container.Context).Inflate(page[page_offset], container, false);
        container.AddView(view);
        if (page_offset == page.Length - 1)
            OnAllPagesAdded();
        return view;
    }

    public MyPagerAdapter(List<string> tab_names)
    {
        this.tab_names = tab_names;
    }

    public override int Count => tab_names.Count;

    public override bool IsViewFromObject(View view, Java.Lang.Object obj) => view == obj;

    
    public string GetTabName(int position) => tab_names[position];
    public override void DestroyItem(ViewGroup container, int position, Java.Lang.Object obj)
                                => container.RemoveView((View)obj);
}

I need an event to be triggers when all pages are instantiated and ready to use. I improvised the OnAllPagesAdded event which is triggered with:

if (page_offset == page.Length - 1)
    OnAllPagesAdded();

triggered when the last page is instantiated. I have set:

view_pager.OffscreenPageLimit = 100;

so all pages will be instantiated from the outset.

Is there a better/safer way to trigger the event OnAllPagesAdded ?

Answer 1

You could add page data in PageScrolled method of ViewPager , it will detect whehter the last page is shown.

For example:

MyPagerAdapter myPagerAdapter = ...
...
viewPager.PageScrolled += ViewPager_PageScrolled;

private void ViewPager_PageScrolled(object sender, ViewPager.PageScrolledEventArgs e)
{
    if(e.Position == page.Length - 1){
        // add page data
        myPagerAdapter.OnAllPagesAdded();
    }
}