效果图：

View代码：

class SignView : View {
    //画笔
    private val mGesturePaint = Paint()
    private val mTextPaint = Paint()

    //路径
    private val mPath = Path()

    //起点X,Y
    private var mX = 0F
    private var mY = 0F

    //缓存的画布
    private lateinit var mCacheCanvas: Canvas

    //生成的图片
    private lateinit var mCacheBitmap: Bitmap

    //背景提示文案 不需要展示在最终生成的图片中 当有按下事件，即赋值为true
    var hintTextIsClear = false


    constructor(context: Context) : super(context)
    constructor(context: Context, attrs: AttributeSet) : super(context, attrs)
    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int) : super(context, attrs, defStyleAttr)

    init {
        with(mGesturePaint) {
            isAntiAlias = true//坑锯齿
            style = Paint.Style.STROKE
            strokeWidth = 10F//画笔宽度
            color = Color.BLACK
        }

        with(mTextPaint) {
            isAntiAlias = true//坑锯齿
            textSize = 120F
            color = Color.parseColor("#cccccc")
        }
    }

    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        //创建根view一样大的bitmap，用来保存签名（当控件大小发生改变时调用）
        mCacheBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
        mCacheCanvas = Canvas(mCacheBitmap)
        mCacheCanvas.drawColor(Color.TRANSPARENT)

        //背景提示文案
        val textWidth: Float = AnnulusUtil.calcTextWidth(mTextPaint, "请在此签名").toFloat()
        mCacheCanvas.drawText("请在此签名", width / 2F - (textWidth / 2), height / 2F, mTextPaint)
    }

    override fun onTouchEvent(event: MotionEvent?): Boolean {
        when (event?.action) {
            MotionEvent.ACTION_DOWN -> {
                touchDown(event)
            }
            MotionEvent.ACTION_MOVE -> {
                touchMove(event)
            }
            MotionEvent.ACTION_UP -> {
                //将路径画到Bitmap，即一笔画完才更新bitmap，不会那么频繁，但是轨迹路径还是实时显示在画板上
                mCacheCanvas.drawPath(mPath, mGesturePaint)
                //清空路径
                mPath.reset()
            }
        }
        invalidate()
        return true
    }

    override fun onDraw(canvas: Canvas?) {
        super.onDraw(canvas)
        //画此次笔画之前的内容，内容已保存在mCacheBitmap
        canvas?.drawBitmap(mCacheBitmap, 0F, 0F, mGesturePaint)
        //实时画路径
        canvas?.drawPath(mPath, mGesturePaint)
    }

    private fun touchDown(event: MotionEvent?) {
        if (!hintTextIsClear) {
            clear()
            hintTextIsClear = true
        }

        //清空路径
        mPath.reset()
        val startX = event?.x ?: 0F
        val startY = event?.y ?: 0F
        mX = startX
        mY = startY
        //设置路径的起点
        mPath.moveTo(startX, startY)
    }

    private fun touchMove(event: MotionEvent?) {
        val x = event?.x ?: 0F
        val y = event?.y ?: 0F

        val previousX = mX
        val previousY = mY

        //平滑曲线，previousX, previousY控制点，x,y结束点
        mPath.quadTo(previousX, previousY, x, y)
        mX = x
        mY = y
    }

    public fun clear() {
        mCacheCanvas?.run {
            drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR)
        }
    }

    public fun getBitMap(): Bitmap {
        val bitmap = mCacheBitmap
        //20kb
        ImageUtils.compressByQuality(bitmap, 20 * 1024L)
        return bitmap
    }

    public fun getBitmapFile(): File {
        val file = File(Environment.getExternalStorageDirectory(), "${System.currentTimeMillis()}.png")
        val fileOutputStream = FileOutputStream(file)
        try {
            fileOutputStream.write(ImageUtils.bitmap2Bytes(getBitMap()))
            fileOutputStream.flush()
            fileOutputStream.close()
        } catch (e: IOException) {
            e.printStackTrace()
        }
        return file
    }

}

计算文字长宽

/**
     * calculates the approximate width of a text, depending on a demo text
     * avoid repeated calls (e.g. inside drawing methods)
     *
     * @param paint
     * @param demoText
     * @return
     */
    fun calcTextWidth(paint: Paint, demoText: String?): Int {
        return paint.measureText(demoText).toInt()
    }

    private val mCalcTextHeightRect = Rect()

    /**
     * calculates the approximate height of a text, depending on a demo text
     * avoid repeated calls (e.g. inside drawing methods)
     *
     * @param paint
     * @param demoText
     * @return
     */
    fun calcTextHeight(paint: Paint, demoText: String): Int {
        val r = mCalcTextHeightRect
        r[0, 0, 0] = 0
        paint.getTextBounds(demoText, 0, demoText.length, r)
        return r.height()
    }

xml中使用：

<xxxxxxxx.view.SignView
        android:id="@+id/sign_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="10dp"
        android:background="@drawable/shape_dash_corner_8" />

虚线边框被灰色背景

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <stroke
        android:width="1dp"
        android:color="@color/text_color_cccccc"
        android:dashWidth="2dp"
        android:dashGap="2dp" />
    <corners android:radius="8dp" />
    <solid android:color="@color/f8f8f8" />
</shape>