安卓 WebView：检测滚动

Question

我需要知道如何检测用户在webView中是否已经无法滚动。当用户向左或向右滑动时，我想生成一个动作，但前提是用户无法滚动：

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

- Carbodrache

Answer 1

我找到了一个对我有用的解决方案，我查看了2.3 API中WebView类的源代码，并找到了如何在2.1 API中实现它。也许它可以适用于旧版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);
    }

}

- Carbodrache

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当内容放大或缩小时，这不起作用。有什么解决办法吗？ - Chitrang

Answer 2

API中有一些有趣的方法，但它们是受保护的。我认为您可以创建自己的WebView（扩展WebView），使用这些方法并使它们公开可用。 具体来说，也许您可以使用这两个方法： onScrollChanged 和 onOverScroll.

- mdelolmo

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onOverScroll方法适用于Android 2.3，因此我将获取WebView的2.3源代码并将其包含在我的项目中。 - Carbodrache

Answer 3

我认为这会解决这个问题：

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);

- Liang