Android自定义控件（二）——有弹性的ScrollView

本文在http://gundumw100.iteye.com/blog/1075286的基础上稍作修改，

实现了当手指滑动到ScrollView的顶部、底部时，

可以继续的向上、向下拉伸。当释放手指的时候，向上、下弹回。

效果如图所示：

主要代码：

public class ElasticScrollView extends ScrollView {
    private View inner;
    private float y;
    private Rect normal = new Rect();
    private boolean animationFinish = true;

    public ElasticScrollView(Context context) {
        super(context);
    }

    public ElasticScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onFinishInflate() {
        if (getChildCount() > 0) {
            inner = getChildAt(0);
        }
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (inner == null) {
            return super.onTouchEvent(ev);
        } else {
            commOnTouchEvent(ev);
        }
        return super.onTouchEvent(ev);
    }

    public void commOnTouchEvent(MotionEvent ev) {
        if (animationFinish) {
            int action = ev.getAction();
            switch (action) {
            case MotionEvent.ACTION_DOWN:
//              System.out.println("ACTION_DOWN");
                y = ev.getY();
                super.onTouchEvent(ev);
                break;
            case MotionEvent.ACTION_UP:
//              System.out.println("ACTION_UP");
                y = 0;
                if (isNeedAnimation()) {
                    animation();
                }
                super.onTouchEvent(ev);
                break;
            case MotionEvent.ACTION_MOVE:
//              System.out.println("ACTION_MOVE");
                final float preY = y == 0 ? ev.getY() : y;
                float nowY = ev.getY();
                int deltaY = (int) (preY - nowY);
                // 滚动
//              scrollBy(0, deltaY);

                y = nowY;
                // 当滚动到最上或者最下时就不会再滚动，这时移动布局
                if (isNeedMove()) {
                    if (normal.isEmpty()) {
                        // 保存正常的布局位置
                        normal.set(inner.getLeft(), inner.getTop(), inner.getRight(), inner.getBottom());
                    }
                    // 移动布局
                    inner.layout(inner.getLeft(), inner.getTop() - deltaY / 2, inner.getRight(), inner.getBottom() - deltaY / 2);
                } else {
                    super.onTouchEvent(ev);
                }
                break;
            default:
                break;
            }
        }
    }

    // 开启动画移动

    public void animation() {
        // 开启移动动画
        TranslateAnimation ta = new TranslateAnimation(0, 0, 0, normal.top - inner.getTop());
        ta.setDuration(200);
        ta.setAnimationListener(new AnimationListener() {
            @Override
            public void onAnimationStart(Animation animation) {
                animationFinish = false;

            }

            @Override
            public void onAnimationRepeat(Animation animation) {

            }

            @Override
            public void onAnimationEnd(Animation animation) {
                inner.clearAnimation();
                // 设置回到正常的布局位置
                inner.layout(normal.left, normal.top, normal.right, normal.bottom);
                normal.setEmpty();
                animationFinish = true;
            }
        });
        inner.startAnimation(ta);
    }

    // 是否需要开启动画
    public boolean isNeedAnimation() {
        return !normal.isEmpty();
    }

    // 是否需要移动布局
    public boolean isNeedMove() {
        int offset = inner.getMeasuredHeight() - getHeight();
        int scrollY = getScrollY();
        if (scrollY == 0 || scrollY == offset) {
            return true;
        }
        return false;
    }

}