如何通过所需的像素值检测ScrollView滚动

Question

I'm extending ScrollView to detect if it was scrolled up or down. I want to add option to detect scroll only if it was scrolled by let's say 50 pixels. How to do that? My current code of scrollview overrides onScrollChanged:

public interface OnDetectScrollListener {
    void onUpScroll();
    void onDownScroll();
}

public class MyScrollView extends ScrollView {

    private OnDetectScrollListener onDetectScrollListener = null;
    private boolean scrollDown = false;
    private boolean scrollUp = false;

    .... constructors ....

    public void setOnDetectScrollListener(OnDetectScrollListener scrollViewListener) {
        this.onDetectScrollListener = scrollViewListener;
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        if (onDetectScrollListener != null) {
            View view = (View) getChildAt(getChildCount() - 1);
            int diff = (view.getBottom() - (getHeight() + getScrollY()));

            //scroll down
            if(t > oldt){
                if(!scrollDown & oldt >= 0 & t >= 0){
                    scrollDown = true;
                    scrollUp = false;
                    onDetectScrollListener.onDownScroll();
                }

            }
            //scroll up
            else if(t < oldt & diff > 0){
                if(!scrollUp){
                    scrollUp = true;
                    scrollDown = false;
                    onDetectScrollListener.onUpScroll();
                }
            }
        }
    }
}

Answer 1

I don't have much experience in ScrollView but you can do this:

if what you want is to start scrolling only after 50 pixels you can follow this logic:

bool scrolling = false;
int scrollX = -1;
int scrollY = -1;

protected void scroll(int x, int y)
{
    //View was not scrolling
    if (scrollX == -1)
    {
        //Save starting point
        scrollX = x;
    }
    //View keeps scrolling
    else
    {
        //User is touching 50 pixels left from starting point
        if (x -scrollX > 50)
        {
            scrolling = true;
        } else
        //User is touching 50 pixels right from starting point
        if (scrollX -x > 50)
        {
            scrolling = true;
        }
    }

    if (scrolling)
    {
        /* Your code */
    }
}

I'm not sure if either l or t is x or y on your onScrollView (I've never touched it) but you can implement it your way.

Feel free to create separate variables for scrolling left and scrolling right (or up/down).

Please avoid using pixels, especially for input. Prefer using density-independent pixels (dp). More info here (Supporting Multiple Screens .