自定义View系列（四）

自定义View实战之

自定义下拉放大头部图片的ScrollView

一、原理：

• 获得要放大的控件，并获取其宽高
• 在顶部时继续往下拉，通过LayoutParams改变控件的宽高
• 手指抬起时初始化各项参数，通过属性动画回弹控件

二、实现：

public class HeadZoomScrollView extends ScrollView {
    public HeadZoomScrollView(Context context) {
        super(context);
    }

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

    public HeadZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    //用于记录下拉位置
    private float y = 0f;
    //zoomView原本的宽高
    private int zoomViewWidth = 0;
    private int zoomViewHeight = 0;

    //是否正在放大
    private boolean mScaling = false;

    //放大的view，默认为第一个子view
    private View zoomView;
    public void setZoomView(View zoomView) {
        this.zoomView = zoomView;
    }

    //滑动放大系数，系数越大，滑动时放大程度越大
    private float mScaleRatio = 0.4f;
    public void setmScaleRatio(float mScaleRatio) {
        this.mScaleRatio = mScaleRatio;
    }

    //最大的放大倍数
    private float mScaleTimes = 2f;
    public void setmScaleTimes(int mScaleTimes) {
        this.mScaleTimes = mScaleTimes;
    }

    //回弹时间系数，系数越小，回弹越快
    private float mReplyRatio = 0.5f;
    public void setmReplyRatio(float mReplyRatio) {
        this.mReplyRatio = mReplyRatio;
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        //不可过度滚动，否则上移后下拉会出现部分空白的情况
        setOverScrollMode(OVER_SCROLL_NEVER);
        //获得默认第一个view
        if (getChildAt(0) != null && getChildAt(0) instanceof ViewGroup && zoomView == null) {
            ViewGroup vg = (ViewGroup) getChildAt(0);
            if (vg.getChildCount() > 0) {
                zoomView = vg.getChildAt(0);
            }
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (zoomViewWidth <= 0 || zoomViewHeight <=0) {
            zoomViewWidth = zoomView.getMeasuredWidth();
            zoomViewHeight = zoomView.getMeasuredHeight();
        }
        if (zoomView == null || zoomViewWidth <= 0 || zoomViewHeight <= 0) {
            return super.onTouchEvent(ev);
        }
        switch (ev.getAction()) {
            case MotionEvent.ACTION_MOVE:
                if (!mScaling) {
                    if (getScrollY() == 0) {
                        y = ev.getY();  //滑动到顶部时，记录位置
                    } else {
                        break;
                    }
                }
                int distance = (int) ((ev.getY() - y)*mScaleRatio);
                if (distance < 0) break;  //若往下滑动
                mScaling = true;
                setZoom(distance);
                return true;
            case MotionEvent.ACTION_UP:
                mScaling = false;
                replyView();
                break;
        }
        return super.onTouchEvent(ev);
    }

    /**
     * 放大view
     * @param s
     */
    private void setZoom(float s) {
        float scaleTimes = (float) ((zoomViewWidth+s)/(zoomViewWidth*1.0));
        //如超过最大放大倍数，直接返回
        if (scaleTimes > mScaleTimes) return;

        ViewGroup.LayoutParams layoutParams = zoomView.getLayoutParams();
        layoutParams.width = (int) (zoomViewWidth + s);
        layoutParams.height = (int)(zoomViewHeight*((zoomViewWidth+s)/zoomViewWidth));
        //设置控件水平居中
        ((MarginLayoutParams) layoutParams).setMargins(-(layoutParams.width - zoomViewWidth) / 2, 0, 0, 0);
        zoomView.setLayoutParams(layoutParams);
    }

    /**
     * 回弹
     */
    private void replyView() {
        final float distance = zoomView.getMeasuredWidth() - zoomViewWidth;
        //设置动画
        ValueAnimator anim = ObjectAnimator.ofFloat(distance, 0.0F).setDuration((long) (distance * mReplyRatio));
        anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                setZoom((Float) animation.getAnimatedValue());
            }
        });
        anim.start();
    }

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

    private OnScrollListener onScrollListener;

    public void setOnScrollListener(OnScrollListener onScrollListener) {
        this.onScrollListener = onScrollListener;
    }

    /**
     * 滑动监听
     */
    public interface OnScrollListener{
        void onScroll(int scrollX,int scrollY,int oldScrollX, int oldScrollY);
    }
}