Scrollview listener is not working in Xamarin for Android?

Question

I am using for C# in Xamarin to create an android app. I have created an extension of the scrollview. Here is my code for that

public class EndlessScroll : ScrollView
{ 
    public EndlessScroll (Context context) : base (context)
    {

    }

    public EndlessScroll(Context context, IAttributeSet attrs) : base(context, attrs)
    {



    }

    public EndlessScroll(Context context, IAttributeSet attrs, int defStyle) : base(context, attrs, defStyle)
    {

    }



    public interface OnScrollViewListener
    {
        void onScrollChanged(EndlessScroll v, int l, int t, int oldl, int oldt);
    }

    public  OnScrollViewListener scrollViewListener;

    public void setOnScrollViewListener(OnScrollViewListener scrollViewListener) {
        this.scrollViewListener = scrollViewListener;
    }


    protected   void onScrollChanged(int l, int t, int oldl, int oldt)
    {

        base.OnScrollChanged(l, t, oldl, oldt);
        if (scrollViewListener != null) {
            scrollViewListener.onScrollChanged(this, l, t, oldl, oldt);
          }

    }


}

}

I tried to implement it into another class. I am getting no compile errors but it will not register when the scrollview has hit the bottom. Here is the code I have here.

public class getFromParse:Activity, EndlessScroll.OnScrollViewListener {

    LinearLayout linear; 
    Button buttonSort; 
    Typeface font; 


protected override void OnCreate (Bundle bundle)
    {
        Window.RequestFeature(WindowFeatures.NoTitle);
        base.OnCreate (bundle); 
        SetContentView (Resource.Layout.debugLog);



   EndlessScroll  scroll = FindViewById <EndlessScroll> (Resource.Id.scrollView); 
        scroll.setOnScrollViewListener (this); 

And here is where the scroll view listener is supposed to detect when it hits the bottom.

public  void onScrollChanged(EndlessScroll scrollView, int x, int y, int oldx, int oldy) {
        // We take the last son in the scrollview
        View view = (View) scrollView.GetChildAt(scrollView.ChildCount  - 1);
        int diff = (view.Bottom  - (scrollView.Height + scrollView.ScrollY));

        // if diff is zero, then the bottom has been reached
        if (diff == 0) {
            Console.WriteLine ("Scroll changed"); 
        }
    }

If anybody could help me out and let me know what I am doing wrong, that would be a great help. It seems that I am doing everything right, but I may be missing something.

Answer 1

I found out what I was doing wrong. In case anybody in the future needs to write a scroll listener using c# in Xamarin, here is how I did it.

public class EndlessScroll : ScrollView
{ 
    private ScrollViewListener scrollViewListener = null; 
    public EndlessScroll (Context context) : base (context) 
    {

    }
    public EndlessScroll(Context context, IAttributeSet attrs, int defStyle) : base(context, attrs, defStyle)
    {

    }

    public EndlessScroll(Context context, IAttributeSet attrs) : base(context, attrs)
    {



    }




    public interface ScrollViewListener
    {
        void OnScrollChanged(EndlessScroll v, int l, int t, int oldl, int oldt);
    }



    public void setOnScrollViewListener(ScrollViewListener scrollViewListener) {
        this.scrollViewListener = scrollViewListener;
    }


    protected override void OnScrollChanged(int l, int t, int oldl, int oldt)
    {


        base.OnScrollChanged (l, t, oldl, oldt); 
        if (scrollViewListener != null) {
            scrollViewListener.OnScrollChanged (this, l, t, oldl, oldt);
        } 
    }


}

As you can see I forgot to override the OnScrollChanged.

Make you sure you implement the interface into the activity you want to use it in. Then put this code in your oncreate.

 EndlessScroll  scroll = FindViewById <EndlessScroll> (Resource.Id.scrollView); 


        scroll.setOnScrollViewListener (this); 

Be sure to add the method below so that it can register when the scroll is changed.

public void  OnScrollChanged(EndlessScroll scrollView, int l, int t, int oldl, int oldt) {
        // We take the last son in the scrollview
        View view = (View) scrollView.GetChildAt(scrollView.ChildCount  - 1);
        int diff = (view.Bottom  - (scrollView.Height + scrollView.ScrollY));

        // if diff is zero, then the bottom has been reached
        if (diff <= 0 && myResources.isLoading == false) {
            myResources.isLoading = true; 
           //do stuff here 
        }


    }

As you can see the above code allows it to detect when the scroll has reached the bottom as long as no content is loading.