Question

我知道有一个例子如何在ScrollView上实现反弹效果，但在这里我整天都在努力解决一个问题。我在Parallax ScrollView之间创建了具有反弹效果的东西。 Parallax ScrollView取自Parallax Android ScrollView，并在ObservableScrollView上实现反弹效果，现在看起来像这样：

public class ObservableScrollView extends ScrollView {
private ScrollCallbacks mCallbacks;

private static final int MAX_Y_OVERSCROLL_DISTANCE = 150;

private Context mContext;
private int mMaxYOverscrollDistance;

public ObservableScrollView(Context context, AttributeSet attrs) {
    super(context, attrs);
    this.mContext = context;
    initBounceScrollView();
}

@Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
    super.onScrollChanged(l, t, oldl, oldt);
    if (mCallbacks != null) {
        mCallbacks.onScrollChanged(l, t, oldl, oldt);
    }
}

@Override
public int computeVerticalScrollRange() {
    return super.computeVerticalScrollRange();
}

public void setCallbacks(ScrollCallbacks listener) {
    mCallbacks = listener;
}

private void initBounceScrollView() {
    // get the density of the screen and do some maths with it on the max
    // overscroll distance
    // variable so that you get similar behaviors no matter what the screen
    // size

    final DisplayMetrics metrics = mContext.getResources()
            .getDisplayMetrics();
    final float density = metrics.density;

    mMaxYOverscrollDistance = (int) (density * MAX_Y_OVERSCROLL_DISTANCE);

}

@Override
public void draw(Canvas canvas) {
    super.draw(canvas);
}

static interface ScrollCallbacks {
    public void onScrollChanged(int l, int t, int oldl, int oldt);
}

@SuppressLint("NewApi")
@Override
protected boolean overScrollBy(int deltaX, int deltaY, int scrollX,
        int scrollY, int scrollRangeX, int scrollRangeY,
        int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
    // This is where the magic happens, we have replaced the incoming
    // maxOverScrollY with our own custom variable mMaxYOverscrollDistance;
    return super.overScrollBy(deltaX, deltaY, scrollX, scrollY,
            scrollRangeX, scrollRangeY, maxOverScrollX,
            mMaxYOverscrollDistance, isTouchEvent);
}

现在我想要实现的是对视差scrollview的反弹效果，但我希望只有当我拉下ScrollView时才会出现反弹效果。例如，当我在ScrollView的开头并将其拉下来时。我想在ScrollView结束时禁用跳出效果。

任何建议/想法我如何才能实现这一点......这是创建这样的自定义View的最佳方式吗？

Answer 1

在api 9中引入了onOverscrolled方法。您可以达到如下所需的效果：

 @Override
    protected void onOverScrolled(int scrollX, int scrollY, boolean clampedX, boolean clampedY) {
        if (scrollY < 0)
            super.onOverScrolled(scrollX, scrollY, clampedX, clampedY);
    }

因此只有当您向下拉动滚动视图时才会发生过度滚动，并且滚动变为负数。将其切换为(scrollY > 0)以达到相反的效果。

Android ScrollView仅在拉下时弹跳

1 个答案: