ScrollView ScrollBy方法采用2个参数

Question

ScrollView layout is actually a vertical scroller.

Why the scroll view method takes x parameter while it only scrolls vertically?

Shouldn't it take only the y parameter? since the x parameter is useless.

Any ideas?

Answer 1

Code comes from ScrollView.class .
ScrollView need to call View 's scrollTo(x, y) , so it takes 2 parameters.
Therefore, any View 's subclass, including ScrollView , can scroll by x axis and y axis.

@Override
public void scrollTo(int x, int y) {
    // we rely on the fact the View.scrollBy calls scrollTo.
    if (getChildCount() > 0) {
        View child = getChildAt(0);
        x = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
        y = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
        if (x != mScrollX || y != mScrollY) {
            super.scrollTo(x, y);
        }
    }
}

Then why ScrollView only scrolls in vertical direction?
Look at public boolean onTouchEvent(MotionEvent ev) method in ScrollView .
It only handles ev.getY() !
On the other hand, HorizonalScrollView only handles ev.getX() .

Answer 2

Why the scroll view method takes x parameter while it only scrolls vertically?

This is only the case if your layout file is the same width as your view. Take a look at this thread.

You can also scroll horizontaly using HorizontalScrollView , there you will need the x parameter. Check the developer site for this.

Or you can use this two dimensional scroller shown in this blog to make use of the both of the parameters if needed.