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Android webview : detect scroll

Posted by: admin June 15, 2020 Leave a comment

Questions:

I need to know how to detect if the user can’t scroll anymore in a webView. I want to generate an action when the user swipes to the left or right, but only if the user can’t scroll:

IF the user swipes to the left AND the webview can't scroll to left THEN
 do something
ELSE
 let the webview scroll
How to&Answers:

I found a solution which work for me, I check the source code of class WebView in 2.3 API and find how to do it with a 2.1 API. Maybe it can work with older API:

public class CustomWebView extends WebView {

    private float oldX;

    // indicate if horizontal scrollbar can't go more to the left
    private boolean overScrollLeft = false;

    // indicate if horizontal scrollbar can't go more to the right
    private boolean overScrollRight = false;

    // indicate if horizontal scrollbar can't go more to the left OR right
    private boolean isScrolling = false;

    public CustomWebView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }


    public CustomWebView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
    }



    public CustomWebView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // width of the vertical scrollbar
        int scrollBarWidth = getVerticalScrollbarWidth();

        // width of the view depending of you set in the layout
        int viewWidth = computeHorizontalScrollExtent();

        // width of the webpage depending of the zoom
        int innerWidth = computeHorizontalScrollRange();

        // position of the left side of the horizontal scrollbar
        int scrollBarLeftPos = computeHorizontalScrollOffset();

        // position of the right side of the horizontal scrollbar, the width of scroll is the width of view minus the width of vertical scrollbar
        int scrollBarRightPos = scrollBarLeftPos + viewWidth - scrollBarWidth;

        // if left pos of scroll bar is 0 left over scrolling is true
        if(scrollBarLeftPos == 0) {
            overScrollLeft = true;
        } else {
            overScrollLeft = false;
        }

        // if right pos of scroll bar is superior to webpage width: right over scrolling is true
        if(scrollBarRightPos >= innerWidth) {
            overScrollRight = true;
        } else {
            overScrollRight = false;
        }

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN: // when user touch the screen
            // if scrollbar is the most left or right
            if(overScrollLeft || overScrollRight) {
                isScrolling = false;
            } else {
                isScrolling = true;
            }
            oldX = event.getX();
            break;

        case MotionEvent.ACTION_UP: // when user stop to touch the screen
            // if scrollbar can't go more to the left OR right 
            // this allow to force the user to do another gesture when he reach a side
            if(!isScrolling) {
                if(event.getX() > oldX && overScrollLeft) {
                    // left action
                }

                if(event.getX() < oldX && overScrollRight) {
                    // right actio
                }
            }

            break;
        default:
            break;
        }
        return super.onTouchEvent(event);
    }

}

Answer:

There are some interesting methods in the API, but they are protected, I think you can create your own WebView (extend WebView) and use those methods and make them public.
specifically, maybe you can use these two
onScrollChanged and onOverScroll.

Answer:

I think this will solve this problem:

int horizontalOffset = computeHorizontalScrollOffset();
int contentWidth = (int) Math.floor(getContentWidth() * getScale());
int viewportWidth = getWidth();

// 1 just for random error
boolean reachRightEnd = ((horizontalOffset +  viewportWidth) >= (contentWidth - 1));
boolean reachLeftEnd = (horizontalOffset == 0);