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我的例子继承ConstraintLayout，把要拖动的view在xml中 tag设置为float，其他的view按正常的ConstraintLayout用法使用即可，互不影响，多个也可tag设为float

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原理：基于ViewDragHelper，view的拖拽按正常处理，抬手时判断位置决定贴边可参考鸿洋的教程

/**
 * Created by 不听话的好孩子 on 2018/1/26.
 * 子viewTag为float会被抓住
 */
class FloatLayout @JvmOverloads constructor(
        context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : ConstraintLayout(context, attrs, defStyleAttr) {
    var MOVE_FLAT = "float"
    var sticky = true
    private var viewDragHelper: ViewDragHelper? = null
    val callback = object : ViewDragHelper.Callback() {
        override fun tryCaptureView(child: View?, pointerId: Int)= MOVE_FLAT == child?.tag

        //限制view上下边界
        override fun clampViewPositionVertical(child: View, top: Int, dy: Int): Int {
            var verticalscroll = 0
            if (top > height - child.height) {
                verticalscroll = height - child.height
            } else {
                if (top > 0)
                    verticalscroll = top
            }
            return verticalscroll
        }
        //限制view左右边界
        override fun clampViewPositionHorizontal(child: View, left: Int, dx: Int): Int {
            var horizontalScroll = 0
            if (left > width - child.width) {
                horizontalScroll = width - child.width
            } else {
                if (left > 0)
                    horizontalScroll = left
            }
            return horizontalScroll
        }

        override fun getViewVerticalDragRange(child: View): Int {
            return height - child.height
        }

        override fun getViewHorizontalDragRange(child: View): Int {
            return width - child.width
        }
         
//放手时贴边
        override fun onViewReleased(releasedChild: View, xvel: Float, yvel: Float) {
            if (sticky) {
                if (releasedChild.left + releasedChild.width / 2 > width / 2) {
                    viewDragHelper?.settleCapturedViewAt(width - releasedChild.width, releasedChild.top)
                } else {
                    viewDragHelper?.settleCapturedViewAt(0, releasedChild.top)
                }
                invalidate()
            }
        }
    }

    override fun computeScroll() {
        if (viewDragHelper!!.continueSettling(true)) {
           invalidate()
        }
    }

    init {
        viewDragHelper = ViewDragHelper.create(this, 1f, callback)
    }

    override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
        return viewDragHelper!!.shouldInterceptTouchEvent(ev)
    }


//手指放下的地方在float子view上处理事件
    override fun onTouchEvent(event: MotionEvent): Boolean {
        viewDragHelper?.processTouchEvent(event)
        return true
    }
}