Android-自定义ViewGroup(二) 侧滑菜单

为加深自定义ViewGroup实现思想,所以自己写了一个SlidingMenu,实现方式类似
Android-自定义ViewGroup(一) 水平滑动;优点在于添加了SlidingMenu的padding(onMeasure中测量,onLayout中布局)及子ViewGroup的Margin(onLayout中布局)。
  下面说实现思想:SlidingMenu中添加两个布局
(1)onMeasure中先对子ViewGroup进行测量,调用measureChildren()方法;measureChildren(widthMeasureSpec, heightMeasureSpec);其次要设置自身SlidingMenu的宽高,当int widthMode = MeasureSpec.getMode(widthMeasureSpec)
得到mode为EXACTLY时,设置getSize得到的宽高,其他模式时对子ViewGroup进行测量得到所有子ViewGroup宽高的总和,传入setMeasuredDimension(),如下:
setMeasuredDimension(widthMode == MeasureSpec.EXACTLY ? widthSize : width, heightMode == MeasureSpec.EXACTLY ? heightSize : height);
onMeasure代码如下:

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        measureChildren(widthMeasureSpec, heightMeasureSpec);

        //menu、content总宽
        int width = 0;
        //menu、content总高
        int height = 0;
        //可以单独获取子ViewGroup并测量宽高,此处用for是因为所有自定义ViewGroup都适用。
        for (int i = 0; i < getChildCount(); i++) {
            View child = getChildAt(i);
            //必须重写generateLayoutParams(attrs)方法,设置适当的LayoutParams
            MarginLayoutParams childLp = (MarginLayoutParams) child.getLayoutParams();
            //单独的宽高
            width += child.getMeasuredWidth() + childLp.leftMargin + childLp.rightMargin;
            height += child.getHeight() + childLp.topMargin + childLp.bottomMargin;
            //menuWidth为menu的宽,考虑了此ViewGroup的leftPadding值,用作onTouch限定滑动边界、onLayout布局
            if (i == 0) {
                menuWidth = getPaddingLeft() + childLp.leftMargin + childLp.rightMargin + child.getMeasuredWidth();
            }
        }
        width += getPaddingLeft() + getPaddingRight();
        height += getPaddingTop() + getPaddingBottom();
        //精确模式设置测量得到的尺寸,否则去设置子ViewGroup的宽高测量总和
        setMeasuredDimension(widthMode == MeasureSpec.EXACTLY ? widthSize : width, heightMode == MeasureSpec.EXACTLY ? heightSize : height);
    }

(2)布局只要注意将SlidingMenu的padding和子ViewGroup的margin考虑,没什么复杂的,具体看代码:

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {

        //获取此SlidingMenu的leftPadding,布局时无需考虑rightPadding
        int left = getPaddingLeft();
        for (int i = 0; i < getChildCount(); i++) {
            LinearLayout child = (LinearLayout) getChildAt(i);
            if (null != child && child.getVisibility() != GONE) {
                MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
                int lc = left + lp.leftMargin;
                int tc = lp.topMargin + getPaddingTop();
                int rc = lc + child.getMeasuredWidth();
                int bc = tc + child.getMeasuredHeight();

                //menuWidth为左边菜单宽度
                child.layout(lc - menuWidth, tc, rc - menuWidth, bc);
                left += rc + lp.rightMargin;
            }
        }
    }

(3)注意:以上即完成了SlidingMenu的布局,但是注意我们控件继承的是ViewGroup,通过child.getLayoutParams()拿到的是ViewGroup的布局管理器,需重写该方法的返回值拿到我们要的margin属性。如下:

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }

关于MarginLayoutParams可以去看下,它是ViewGroup的子类,又是包括LinearLayout、RelativeLayout、RecyclerVeiw等布局管理器的父类,可以去了解下。

layoutparms.png

(4)以上就完成了SlidingMenu的布局,此时我们要处理滑动事件,处理滑动事件时首先得确定手指左右滑动,并拦截交由SlidingMenu自身去消费事件。拦截与消费即在onInterceptTouchEvent、onTouchEvent判断水平移动时return true。并在onTouchEvent的MotionEvent.ACTION_MOVE中通过Scroller去设置滑动;

关于Scroller的固定用法如下:

    Scroller scroller = new Scroller(getContext());

    int scrollX = getScrollX();
    int delta = destx - scrollX;
    //300ms内滑向destX,效果就是慢慢滑动
    scroller.startScroll(scrollX, 0, delta, 0, 300);
    invalidate();

    /**
     * 滚动时需要重写的方法,用于控制滚动
     */
    @Override
    public void computeScroll() {
        //判断滚动时候停止
        if (scroller.computeScrollOffset()) {
            //滚动到指定的位置
            scrollTo(scroller.getCurrX(), scroller.getCurrY());
            //这句话必须写,否则不能实时刷新
            postInvalidate();
        }
    }

另外VelocityTracker速度追踪器,及TouchSlop最小有效滑动距离的概念比较简单,有兴趣的可自行了解

下面是该SlidIngMenu的所有代码:

public class ZhanfSlideMenu extends ViewGroup {

    private Scroller scroller;
    private VelocityTracker velocityTracker;

    public ZhanfSlideMenu(Context context) {
        this(context, null);
    }

    public ZhanfSlideMenu(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

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

    private void init() {

        scroller = new Scroller(getContext());
        velocityTracker = VelocityTracker.obtain();
        int touchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();

    }

    /**
     * 滚动时需要重写的方法,用于控制滚动
     */
    @Override
    public void computeScroll() {
        //判断滚动时候停止
        if (scroller.computeScrollOffset()) {
            //滚动到指定的位置
            scrollTo(scroller.getCurrX(), scroller.getCurrY());
            //这句话必须写,否则不能实时刷新
            postInvalidate();
        }
    }

    //分别记录上次滑动的坐标
    private int mLastX = 0;
    private int mLastY = 0;

    //分别记录上次滑动的坐标(onINterceptTouchEvent)
    private int mLastXIntercept = 0;
    private int mLastYIntercept = 0;

    int menuWidth;
    //要移动的点的位置
    int destx;

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                //如果动画还没有结束,再次点击时结束上次动画,即开启这次新的ACTION_DOWN的动画
                if (!scroller.isFinished()) {
                    scroller.abortAnimation();
                }
                break;
            case MotionEvent.ACTION_MOVE:
                int deltaX = x - mLastXIntercept;
                int deltaY = y - mLastYIntercept;
                if (Math.abs(deltaX) > Math.abs(deltaY)) {
                    return true;
                }
                break;
            case MotionEvent.ACTION_UP:

                break;
            default:
                break;
        }
        mLastX = x;
        mLastY = y;
        mLastXIntercept = x;
        mLastYIntercept = y;
        return super.onInterceptTouchEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        velocityTracker.addMovement(event);
        velocityTracker.computeCurrentVelocity(1000);

        int x = (int) event.getX();
        int y = (int) event.getY();
        int scrollX = getScrollX();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                //如果动画还没有结束,再次点击时结束上次动画,即开启这次新的ACTION_DOWN的动画
                if (!scroller.isFinished()) {
                    scroller.abortAnimation();
                }
                break;
            case MotionEvent.ACTION_MOVE:
                int deltaX = x - mLastX;
                int deltaY = y - mLastY;
                if (Math.abs(deltaX) > Math.abs(deltaY) && scrollX >= -menuWidth && scrollX <= 0) {
                    scrollBy(-deltaX, 0);
                }

                break;
            case MotionEvent.ACTION_UP:
                int xVelocity = (int) velocityTracker.getXVelocity();//获取X方向手指滑动的速度,之前必须调用computeCurrentVelocity()方法
                int yVelocity = (int) velocityTracker.getYVelocity();
                if (Math.abs(xVelocity) > 200 && Math.abs(xVelocity) > Math.abs(yVelocity)) {
                    destx = xVelocity > 0 ? (-menuWidth) : 0;
                } else {
                    destx = (scrollX < (-menuWidth / 2)) ? (-menuWidth) : 0;
                }

                int delta = destx - scrollX;
                scroller.startScroll(scrollX, 0, delta, 0, 300);
                invalidate();
                break;
            default:
                break;
        }

        mLastX = x;
        mLastY = y;

        return true;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        measureChildren(widthMeasureSpec, heightMeasureSpec);

        //menu、content总宽
        int width = 0;
        //menu、content总高
        int height = 0;
        //可以单独获取子ViewGroup并测量宽高,此处用for是因为所有自定义ViewGroup都适用。
        for (int i = 0; i < getChildCount(); i++) {
            View child = getChildAt(i);
            //必须重写generateLayoutParams(attrs)方法,设置适当的LayoutParams
            MarginLayoutParams childLp = (MarginLayoutParams) child.getLayoutParams();
            //单独的宽高
            width += child.getMeasuredWidth() + childLp.leftMargin + childLp.rightMargin;
            height += child.getHeight() + childLp.topMargin + childLp.bottomMargin;
            //menuWidth为menu的宽,考虑了此ViewGroup的leftPadding值,用作onTouch限定滑动边界、onLayout布局
            if (i == 0) {
                menuWidth = getPaddingLeft() + childLp.leftMargin + childLp.rightMargin + child.getMeasuredWidth();
            }
        }
        width += getPaddingLeft() + getPaddingRight();
        height += getPaddingTop() + getPaddingBottom();
        //精确模式设置测量得到的尺寸,否则去设置子ViewGroup的宽高测量总和
        setMeasuredDimension(widthMode == MeasureSpec.EXACTLY ? widthSize : width, heightMode == MeasureSpec.EXACTLY ? heightSize : height);
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {

        //获取此SlidingMenu的leftPadding,布局时无需考虑rightPadding
        int left = getPaddingLeft();
        for (int i = 0; i < getChildCount(); i++) {
            LinearLayout child = (LinearLayout) getChildAt(i);
            if (null != child && child.getVisibility() != GONE) {
                MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
                int lc = left + lp.leftMargin;
                int tc = lp.topMargin + getPaddingTop();
                int rc = lc + child.getMeasuredWidth();
                int bc = tc + child.getMeasuredHeight();

                //menuWidth为左边菜单宽度
                child.layout(lc - menuWidth, tc, rc - menuWidth, bc);
                left += rc + lp.rightMargin;
            }
        }
    }
}

Qusetion:关于实现SlidingMenu的实现就是这么简单,但也遇上了一个问题,就是在onTouchEvent的Move事件中设置了左右边界,当在边界处手指慢慢移动左右边界正常显示不会滑动。但是当在边界处快速滑动的时候,左右能继续弹性滑动一小段距离,可以看到白色的背景。关于这个问题有待进一步研究。

参考:
《Android开发艺术探索》

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