前言

之前跟着康师傅学习 Android开发自定义控件系列课程时看到 笔记Android自定义控件的分类 里有这么一个效果，如下图

然后我通过搜索引擎搜到了这篇文章（Android超高仿QQ附近的人搜索展示），根据这篇文章我对源码进行了重构、优化，实现了 使用普通自定义 View 实现雷达扫描效果版本 和 使用自定义 SurfaceView 实现雷达扫描效果版本，具体实现过程就不讲了，同学们看代码和注释吧！

自定义 View 与 自定义 SurfaceView

那么，我们来看看 普通自定义 View 和 自定义 SurfaceView 之间的关系吧！

What is a SurfaceView ?

• A view in your app's view hierarchy that has its own separate surface.
• A view that directly accesses a lower-level drawing surface.
• A view that is not part of the view hierarchy.
• A view that can be drawn to from a separate thread.

什么是 SurfaceView ？

• 应用程序的视图层次结构中的一个视图，它有自己独立的表面。
• 直接访问低层绘图图面的视图。
• 不属于视图层次结构的视图。
• 可以从单独的线程绘制的视图。

What is the most distinguishing benefit of using a SurfaceView ?

• A SurfaceView can make an app more responsive to user input.
• You can move drawing operations away from the UI thread.
• Your animations may run more smoothly.

使用 SurfaceView 最显著的好处是什么?

• SurfaceView 可以让应用对用户输入的响应更灵敏。
• 你可以把绘图操作从 UI 线程移开。
• 你的动画可以运行得更流畅。

When should you consider using a SurfaceView ? Select up to three.

• When your app does a lot of drawing, or does complex drawing.
• When your app combines complex graphics with user interaction.
• When your app uses a lot of images as backgrounds.
• When your app stutters, and moving drawing off the UI thread could improve performance.

什么时候应该考虑使用 SurfaceView ?

• 当你的应用需要大量绘图或复杂绘图时。
• 当你的应用程序结合了复杂的图形和用户交互。
• 当你的应用程序使用很多图片作为背景时。
• 当你的应用程序出现问题时，移动 UI 线程可以提高性能。

以上摘抄自 谷歌官方文档 ，当然里面有一个小例子，同学们可以跟着官方的例子去实现自定义 SurfaceView 哈~

最显著的区别就是普通view和它的宿主窗口共享一个绘图表面（Surface），SurfaceView 虽然也在 View 的树形结构中，但是它有属于自己的绘图表面，Surface 内部持有一个 Canvas ，可以利用这个 Canvas 绘制。

摘抄自：SurfaceView和普通view的区别及简单使用

资源图片

universe_bg.jpg

circle_photo.png

使用普通自定义 View 实现雷达扫描效果版本

import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.util.Log
import android.view.View
import cn.cqautotest.imui.R
import kotlin.math.min

/**
 * 使用普通自定义 View 实现雷达扫描效果
 *
 * @property drawing Boolean
 * @property mPaintBackground Paint
 * @property mPaintLine Paint
 * @property mPaintCircle Paint
 * @property mPaintScan Paint
 * @property mDiameter Int
 * @property mRadius Int
 * @property mRect Rect
 * @property mMatrix Matrix
 * @property mCurrentScanRotateAngle Int
 * @property mBackgroundMipmap (android.graphics.Bitmap..android.graphics.Bitmap?)
 * @property mCenterBitmap Bitmap
 * @property mCircleProportions Array<Float>
 * @property mScanRotateSpeed Int
 * @property mCurrentScanCount Int
 * @property mMaxScanItemCount Int
 * @property mCurrentScanItem Int
 * @property mScan Boolean
 * @property mListener IScanListener
 */
class RadarScanView : View {

    // 是否绘制
    private var drawing: Boolean = false

    // 画背景需要用到的画笔
    private val mPaintBackground: Paint by lazy {
        Paint().apply {
            isAntiAlias = true
            style = Paint.Style.STROKE
        }
    }

    // 画圆线需要用到的画笔
    private val mPaintLine: Paint by lazy {
        Paint().apply {
            color = Color.parseColor("#3C8EAE")
            isAntiAlias = true
            strokeWidth = 1f
            style = Paint.Style.STROKE
        }
    }

    // 画圆需要用到的 paint画笔
    private val mPaintCircle: Paint by lazy {
        Paint().apply {
            color = Color.WHITE
            isAntiAlias = true
        }
    }

    // 画扫描需要用到的画笔
    private val mPaintScan: Paint by lazy {
        Paint().apply {
            style = Paint.Style.FILL_AND_STROKE
        }
    }

    // 圆的直径大小
    private var mDiameter: Int = 0

    // 圆的半径大小
    private var mRadius: Int = 0

    // 矩形
    private lateinit var mRect: Rect

    // 旋转需要使用到的矩阵
    private val mMatrix by lazy {
        Matrix()
    }

    // 当前旋转的角度
    private var mCurrentScanRotateAngle: Int = 0

    // 背景的图片资源
    private val mBackgroundMipmap = BitmapFactory.decodeResource(resources, R.drawable.universe_bg)

    // 中间的图片资源
    private var mCenterBitmap: Bitmap =
        BitmapFactory.decodeResource(resources, R.drawable.circle_photo)

    // 每层圆圈所占的比例
    private val mCircleProportions: Array<Float> =
        arrayOf(1 / 13f, 2 / 13f, 3 / 13f, 4 / 13f, 5 / 13f, 6 / 13f)

    // 扫描时的旋转速度
    private var mScanRotateSpeed = 5

    // 当前扫描的次数
    private var mCurrentScanCount: Int = 0

    // 最大扫描次数
    private var mMaxScanItemCount: Int = 1

    // 当前扫描显示的 Item
    private var mCurrentScanItem: Int = 0

    // 只有设置数据后才开始扫描
    private var mScan: Boolean = false

    // 扫描时的回调接口
    private lateinit var mListener: IScanListener

    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 {
        drawing = true
        // 保持屏幕常亮
        keepScreenOn = true
        // 设置在触摸模式下此视图是否可以接收焦点。将其设置为true也将确保该视图可聚焦。
        isFocusableInTouchMode = true
    }

    override fun onAttachedToWindow() {
        super.onAttachedToWindow()
        drawing = true
        post(object : Runnable {
            override fun run() {
                if (drawing) {
                    calc()
                    invalidate()
                    // 可以通过改变 postDelayed() 方法的第二个参数 delayMillis 调节扫描的速度
                    postDelayed(this, 10)
                } else {
                    removeCallbacks(this)
                }
            }
        })
    }

    override fun onDetachedFromWindow() {
        super.onDetachedFromWindow()
        drawing = false
    }

    /**
     * 进行计算
     */
    private fun calc() {
        mCurrentScanRotateAngle = (mCurrentScanRotateAngle + mScanRotateSpeed) % 360
        mMatrix.postRotate(mScanRotateSpeed.toFloat(), mRadius.toFloat(), mRadius.toFloat())
        // 开始扫描显示标志为 true 且 只扫描一周
        if (mScan && mCurrentScanCount <= (360 / mScanRotateSpeed) && ::mListener.isInitialized) {
            if (mCurrentScanCount % mScanRotateSpeed == 0 && mCurrentScanItem < mMaxScanItemCount) {
                mListener.onScanning(mCurrentScanItem, mCurrentScanRotateAngle)
                mCurrentScanItem++
            }
            if (mCurrentScanItem == mMaxScanItemCount) {
                mListener.onScanSuccess()
            }
            mCurrentScanCount++
        }
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        // 测量
        setMeasuredDimension(getMeasureSize(widthMeasureSpec), getMeasureSize(heightMeasureSpec))
    }

    /**
     * 获取尺寸
     *
     * @param measureSpec Int
     * @return Int
     */
    private fun getMeasureSize(measureSpec: Int): Int = run {
        val specMode = MeasureSpec.getMode(measureSpec)
        val specSize = MeasureSpec.getSize(measureSpec)
        if (specMode == MeasureSpec.EXACTLY) specSize else {
            // 指定测量大小
            if (specMode == MeasureSpec.AT_MOST) min(300, specSize) else 300
        }
    }

    /**
     * 当视图的大小发生变化时，这个方法会在布局过程中调用
     *
     * @param w Int
     * @param h Int
     * @param oldw Int
     * @param oldh Int
     */
    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        mDiameter = min(w, h)
        mRadius = mDiameter / 2
        mRect = Rect(
            (mRadius - mDiameter * mCircleProportions[0]).toInt(),
            (mRadius - mDiameter * mCircleProportions[0]).toInt(),
            (mRadius + mDiameter * mCircleProportions[0]).toInt(),
            (mRadius + mDiameter * mCircleProportions[0]).toInt()
        )
        Log.d(TAG, "onSizeChanged: ====>w：$w mRadius：$mRadius mDiameter：$mDiameter")
    }

    /**
     * 在这个方法内进行重绘界面的操作
     *
     * @param canvas Canvas
     */
    override fun onDraw(canvas: Canvas) {
        // 绘制的层级由调用的先后顺序决定，先绘制的在下面，后绘制的在上面
        drawBackground(canvas)
        drawCircle(canvas)
        drawScan(canvas)
        drawCenterIcon(canvas)
    }

    /**
     * 绘制背景
     *
     * @param canvas Canvas
     */
    protected fun drawBackground(canvas: Canvas) {
        canvas.drawBitmap(mBackgroundMipmap, 0f, 0f, mPaintBackground)
    }

    /**
     * 绘制圆线圈
     *
     * @param canvas Canvas
     */
    private fun drawCircle(canvas: Canvas) {
        canvas.run {
            for (i in 1..5) {
                drawCircle(
                    mRadius.toFloat(),
                    mRadius.toFloat(),
                    mDiameter * mCircleProportions[i],
                    mPaintLine
                )
            }
        }
    }

    /**
     * 绘制扫描部分
     *
     * @param canvas Canvas
     */
    private fun drawScan(canvas: Canvas) {
        canvas.run {
            save()
            // 只赋值一次，避免在重绘时重复创建对象
            if (mPaintScan.shader == null) {
                mPaintScan.shader = SweepGradient(
                    mRadius.toFloat(), mRadius.toFloat(),
                    intArrayOf(Color.TRANSPARENT, Color.parseColor("#84B5CA")),
                    null
                )
            }
            concat(mMatrix)
            drawCircle(
                mRadius.toFloat(), mRadius.toFloat(), mDiameter * mCircleProportions[4],
                mPaintScan
            )
            restore()
        }
    }

    /**
     * 绘制中间的圆形图标
     *
     * @param canvas Canvas
     */
    private fun drawCenterIcon(canvas: Canvas) {
        canvas.drawBitmap(mCenterBitmap, null, mRect, mPaintCircle)
    }

    interface IScanListener {

        /**
         * 正在扫描（此时还没有扫描完毕）的监听
         *
         * @param position Int 扫描的位置
         * @param scanAngle Int 扫描的角度
         */
        fun onScanning(position: Int, scanAngle: Int)

        /**
         * 扫描成功时的回调
         */
        fun onScanSuccess()
    }

    companion object {
        private const val TAG = "RadarScanView"
    }
}

使用自定义 SurfaceView 实现雷达扫描效果版本

import android.content.Context
import android.graphics.*
import android.os.Build
import android.util.AttributeSet
import android.view.SurfaceHolder
import android.view.SurfaceView
import androidx.annotation.RequiresApi
import cn.cqautotest.imui.R
import kotlin.math.min

/**
 * 使用自定义 SurfaceView 实现雷达扫描效果
 *
 * @property drawing Boolean
 * @property mSurfaceHolder SurfaceHolder
 * @property mPaintBackground Paint
 * @property mPaintLine Paint
 * @property mPaintCircle Paint
 * @property mPaintScan Paint
 * @property mWidth Int
 * @property mHeight Int
 * @property mMatrix Matrix
 * @property mCurrentScanRotateAngle Int
 * @property mBackgroundMipmap (android.graphics.Bitmap..android.graphics.Bitmap?)
 * @property mCenterBitmap Bitmap
 * @property mCircleProportions Array<Float>
 * @property mScanRotateSpeed Int
 * @property mCurrentScanCount Int
 * @property mMaxScanItemCount Int
 * @property mCurrentScanItem Int
 * @property mScan Boolean
 * @property mListener IScanListener
 */
class RadarScanSurfaceView : SurfaceView, SurfaceHolder.Callback, Runnable {

    // 是否绘制
    private var drawing: Boolean = false
    private val mSurfaceHolder: SurfaceHolder by lazy {
        holder
    }

    // 画背景需要用到的画笔
    private val mPaintBackground: Paint by lazy {
        Paint().apply {
            isAntiAlias = true
            style = Paint.Style.STROKE
        }
    }

    // 画圆线需要用到的画笔
    private val mPaintLine: Paint by lazy {
        Paint().apply {
            color = Color.parseColor("#3C8EAE")
            isAntiAlias = true
            strokeWidth = 1f
            style = Paint.Style.STROKE
        }
    }

    // 画圆需要用到的 paint画笔
    private val mPaintCircle: Paint by lazy {
        Paint().apply {
            color = Color.WHITE
            isAntiAlias = true
        }
    }

    // 画扫描需要用到的画笔
    private val mPaintScan: Paint by lazy {
        Paint().apply {
            style = Paint.Style.FILL_AND_STROKE
        }
    }

    // 圆的直径大小
    private var mDiameter: Int = 0

    // 圆的半径大小
    private var mRadius: Int = 0

    // 旋转需要使用到的矩阵
    private val mMatrix by lazy {
        Matrix()
    }

    // 当前旋转的角度
    private var mCurrentScanRotateAngle: Int = 0

    // 背景的图片资源
    private val mBackgroundMipmap = BitmapFactory.decodeResource(resources, R.drawable.universe_bg)

    // 中间的图片资源
    private var mCenterBitmap: Bitmap =
        BitmapFactory.decodeResource(resources, R.drawable.circle_photo)

    // 每层圆圈所占的比例
    private val mCircleProportions: Array<Float> =
        arrayOf(1 / 13f, 2 / 13f, 3 / 13f, 4 / 13f, 5 / 13f, 6 / 13f)

    // 扫描时的旋转速度
    private var mScanRotateSpeed = 5

    // 当前扫描的次数
    private var mCurrentScanCount: Int = 0

    // 最大扫描次数
    private var mMaxScanItemCount: Int = 1

    // 当前扫描显示的 Item
    private var mCurrentScanItem: Int = 0

    // 只有设置数据后才开始扫描
    private var mScan: Boolean = false

    // 扫描时的回调接口
    private lateinit var mListener: RadarScanSurfaceView.IScanListener

    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 {
        drawing = true
        // 保持屏幕常亮
        keepScreenOn = true
        // 设置在触摸模式下此视图是否可以接收焦点。将其设置为true也将确保该视图可聚焦。
        isFocusableInTouchMode = true
        //注册回调方法
        mSurfaceHolder.addCallback(this)
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        // 测量
        setMeasuredDimension(getMeasureSize(widthMeasureSpec), getMeasureSize(heightMeasureSpec))
    }

    /**
     * 获取尺寸
     *
     * @param measureSpec Int
     * @return Int
     */
    private fun getMeasureSize(measureSpec: Int): Int = run {
        val specMode = MeasureSpec.getMode(measureSpec)
        val specSize = MeasureSpec.getSize(measureSpec)
        if (specMode == MeasureSpec.EXACTLY) specSize else {
            if (specMode == MeasureSpec.AT_MOST) min(300, specSize) else 300
        }
    }

    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        mDiameter = min(w, h)
        mRadius = mDiameter / 2
    }

    /**
     * Surface 创建时触发
     *
     * @param holder SurfaceHolder
     */
    override fun surfaceCreated(holder: SurfaceHolder) {
        drawing = true
        // 创建子线程，在子线程中进行持续绘制
        Thread(this).start()
    }

    /**
     * Surface 大小或格式发生变化时触发，在 surfaceCreated() 方法调用后该函数至少会被调用一次
     *
     * @param holder SurfaceHolder
     * @param format Int
     * @param width Int
     * @param height Int
     */
    override fun surfaceChanged(holder: SurfaceHolder, format: Int, width: Int, height: Int) {

    }

    /**
     * 销毁时触发，一般不可见时就会销毁
     *
     * @param holder SurfaceHolder
     */
    override fun surfaceDestroyed(holder: SurfaceHolder) {
        drawing = false
    }

    @RequiresApi(Build.VERSION_CODES.O)
    override fun run() {
        while (drawing) {
            mCurrentScanRotateAngle = (mCurrentScanRotateAngle + mScanRotateSpeed) % 360
            mMatrix.postRotate(mScanRotateSpeed.toFloat(), mRadius.toFloat(), mRadius.toFloat())
            // 捕获以下 lambda 内的所有异常
            runCatching {
                // 锁定并获取硬件画布
                val canvas = holder.lockHardwareCanvas()
                // 绘制的层级由调用的先后顺序决定，先绘制的在下面，后绘制的在上面
                drawBackground(canvas)
                drawCircle(canvas)
                drawScan(canvas)
                drawCenterIcon(canvas)
                // 可以通过阻塞子线程的时间来调节雷达扫描的速度
                Thread.sleep(20)
                // 解锁画布并发布
                holder.unlockCanvasAndPost(canvas)
            }
            // 开始扫描显示标志为 true 且 只扫描一周
            if (mScan && mCurrentScanCount <= (360 / mScanRotateSpeed) && ::mListener.isInitialized) {
                if (mCurrentScanCount % mScanRotateSpeed == 0 && mCurrentScanItem < mMaxScanItemCount) {
                    mListener.onScanning(mCurrentScanItem, mCurrentScanRotateAngle)
                    mCurrentScanItem++
                }
                if (mCurrentScanItem == mMaxScanItemCount) {
                    mListener.onScanSuccess()
                }
                mCurrentScanCount++
            }
        }
    }

    /**
     * 绘制背景
     *
     * @param canvas Canvas
     */
    protected fun drawBackground(canvas: Canvas) {
        canvas.drawBitmap(mBackgroundMipmap, 0f, 0f, mPaintBackground)
    }

    /**
     * 绘制圆线圈
     *
     * @param canvas Canvas
     */
    private fun drawCircle(canvas: Canvas) {
        canvas.run {
            for (i in 1..5) {
                drawCircle(
                    mRadius.toFloat(),
                    mRadius.toFloat(),
                    mDiameter * mCircleProportions[i],
                    mPaintLine
                )
            }
        }
    }

    /**
     * 绘制扫描部分
     *
     * @param canvas Canvas
     */
    private fun drawScan(canvas: Canvas) {
        canvas.run {
            save()
            // 只赋值一次
            if (mPaintScan.shader == null) {
                mPaintScan.shader = SweepGradient(
                    mRadius.toFloat(), mRadius.toFloat(),
                    intArrayOf(Color.TRANSPARENT, Color.parseColor("#84B5CA")),
                    null
                )
            }
            concat(mMatrix)
            drawCircle(
                mRadius.toFloat(),
                mRadius.toFloat(),
                mDiameter * mCircleProportions[5],
                mPaintScan
            )
            restore()
        }
    }

    /**
     * 绘制中间的圆形图标
     *
     * @param canvas Canvas
     */
    private fun drawCenterIcon(canvas: Canvas) {
        canvas.drawBitmap(
            mCenterBitmap, null,
            Rect(
                (mRadius - mDiameter * mCircleProportions[0]).toInt(),
                (mRadius - mDiameter * mCircleProportions[0]).toInt(),
                (mRadius + mDiameter * mCircleProportions[0]).toInt(),
                (mRadius + mDiameter * mCircleProportions[0]).toInt()
            ), mPaintCircle
        )
    }

    interface IScanListener {

        /**
         * 正在扫描（此时还没有扫描完毕）的监听
         *
         * @param position Int 扫描的位置
         * @param scanAngle Int 扫描的角度
         */
        fun onScanning(position: Int, scanAngle: Int)

        /**
         * 扫描成功时的回调
         */
        fun onScanSuccess()
    }

    companion object {
        private const val TAG = "RadarScanSurfaceView"
    }
}

实现效果图

GIF 图录制出来有点卡顿，所以就截图了，大家知道是在一直扫描的就好啦~

请同学们点赞、评论、打赏+关注啦~