主要功能項(xiàng):
1. 可以拖動
2. 拖動完可以自動貼邊
3. 可處理點(diǎn)擊事件 
4. 可變化背景圖(美術(shù)改圖,棄之不用啊,可惜可惜)
   4.1 吸附左邊的時(shí)候,背景為左邊直角右邊圓角的矩形
   4.2 吸附右邊的時(shí)候,背景為右邊直角左邊圓角的矩形
   4.3 移動的時(shí)候,背景為圓角的矩形

第一步.上代碼

class FloatView(context: Context, attributeSet: AttributeSet) :
    RelativeLayout(context, attributeSet) {

    private val MORE_SPACE = 10.0 //移動距離像素,超過才算移動
    private var mView: View? = null

    init {
        mView = LayoutInflater.from(context).inflate(R.layout.layout_float_view, this, true)

        val rotation = ObjectAnimator.ofFloat(mView?.iv_playing_bg, "rotation", 0f, 360f)
        rotation.duration = 15000
        rotation.repeatCount = -1
        rotation.start()
        val scaleX = ObjectAnimator.ofFloat(mView?.iv_playing_bg, "scaleX", 0.5f, 1f, 0.5f)
        scaleX.duration = 15000
        scaleX.repeatCount = -1
        scaleX.start()
        val scaleY = ObjectAnimator.ofFloat(mView?.iv_playing_bg, "scaleY", 0.5f, 1f, 0.5f)
        scaleY.duration = 15000
        scaleY.repeatCount = -1
        scaleY.start()
    }
    
    //控件的寬高
    private var mWidth = 0
    private var mHeight = 0
    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        mWidth = w
        mHeight = h
    }

    //屏幕寬高以及半屏和上下邊距
    private var mScreenWith = 0
    private var mScreenHeight = 0
    private var halfWith = 0
    private var mTop = 0
    private var mBottom = 0

    /**
     * 設(shè)置父布局的大小
     */
    fun setParentSize(width: Int, height: Int, top: Int, bottom: Int) {
        mScreenWith = width
        mScreenHeight = height
        halfWith = width / 2

        mTop = top
        mBottom = bottom
    }

    private var lastX = 0f //按下x
    private var lastY = 0f //按下y
    private var isMove = false //是拖動?
    private var isPress = false //是點(diǎn)擊?
    private var offsetX = 0f  //偏移量x,移動的時(shí)候不加偏移量,按鈕會發(fā)生位置錯誤,手指下會是按鈕的左上角,而不是最初按下位置
    private var offsetY = 0f //偏移量y
    private var isChangeBg = false //吸邊的時(shí)候可以更改變化按鈕的左右兩邊圓角,后面美術(shù)改了個(gè)方圖,不用了,但思路留在這

    override fun onTouchEvent(ev: MotionEvent): Boolean {
        val x = ev.rawX
        val y = ev.rawY
        when (ev.action) {
            MotionEvent.ACTION_DOWN -> {
                isMove = false
                isPress = true
                lastX = x
                lastY = y
                offsetX = getX() - x
                offsetY = getY() - y
            }
            MotionEvent.ACTION_MOVE -> {
                isMove = isMove(ev)
                isPress = if (isMove) {
                    if (!isChangeBg) {
                        isChangeBg = true
                        //思路:這里換背景圖
                    }
                    val xandY = getXandY(x + offsetX, y + offsetY)
                    setX(xandY[0].toFloat())
                    setY(xandY[1].toFloat())
                    false
                } else {
                    true
                }
            }
            MotionEvent.ACTION_UP -> {
                isChangeBg = false
                if (isPress) {
                    callback?.click()
                    isPress = true
                }
                if (isMove) {
                    isMove = false
                }
                if (x != 0f || x != (mScreenWith - mWidth).toFloat()) {
                    if (x <= halfWith) {
                        //在左半邊,吸附左邊
                        if (x >lastX) {
                            animate().setInterpolator(DecelerateInterpolator())
                                .setDuration(500)
                                .xBy(-x - offsetX)
                                .start()
                                //思路:這里換背景圖
                        }
                    } else {
                        //在右半邊,吸附右邊
                        if (x < laxtX) {
                            animate().setInterpolator(DecelerateInterpolator())
                                .setDuration(500)
                                .xBy(mScreenWith - mWidth - x - offsetX)
                                .start()
                               //思路:這里換背景圖
                        }
                    }
                }
            }
        }
        return true
    }

    /**
     * 獲取移動到的x和y
     */
    private fun getXandY(x: Float, y: Float): IntArray {
        val resultX = when {
            x < 0 -> {
                0
                 //思路:這里換背景圖
            }
            x > mScreenWith - mWidth -> {
                mScreenWith - mWidth
                 //思路:這里換背景圖
            }
            else -> {
                x.toInt()
            }
        }
        val resultY: Int = when {
            y < mTop -> {
                mTop
            }
            y > mScreenHeight - mBottom - mWidth -> {
                mScreenHeight - mBottom - mWidth
            }
            else -> {
                y.toInt()
            }
        }
        return intArrayOf(resultX, resultY)
    }


    private var callback: OnClickCallback? = null

    fun setOnClickCallback(callback: OnClickCallback) {
        this.callback = callback
    }

    interface OnClickCallback {
        fun click()
    }

    private fun isMove(ev: MotionEvent): Boolean {
        val x = ev.rawX
        val y = ev.rawY
        val moreSpace =
            Math.sqrt(((x - lastX) * (x - lastX) + (y - lastY) * (y - lastY)).toDouble())
        return moreSpace > MORE_SPACE
    }
}

第二步.上布局

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="@dimen/dp_60"
    android:layout_height="@dimen/dp_60">

    <ImageView
        android:id="@+id/iv_playing_bg"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@mipmap/bg_playing" />

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@mipmap/playing"
        android:layout_margin="@dimen/dp_5" />

</RelativeLayout>

第三步.使用

//設(shè)置可移動范圍,正常是要貼邊手機(jī)兩側(cè),所以僅需要特別標(biāo)注上下邊距,畢竟不能滑動到狀態(tài)欄和底部tab上去
floatView.setParentSize(手機(jī)寬,手機(jī)高,上邊距,下邊距)
//點(diǎn)擊事件嘛,處理點(diǎn)擊后的業(yè)務(wù)
floatView.setOnClickCallback(...)