Android技术分享|【自定义View】实现Material Design的Loading效果

预期效果

实现思路

分析一下这个动画，效果应该是通过两个动画来实现的。

• 一个不停变速伸缩的扇形动画
• 一个固定速度的旋转动画

扇形可以通过canvas#drawArc来实现
旋转动画可以用setMatrix实现
圆角背景可以通过canvas#drawRoundRect实现
还需要一个计时器来实现动画效果

这个View最好能够更方便的修改样式，所以需要定义一个declare-styleable，方便通过布局来修改属性。
这些元素应该包括：

• 最底层的卡片颜色
• 卡片内变局
• 内部长条的颜色
• 长条的粗细
• 长条的距离中心的半径
• 字体大小
• 字体颜色

因为用到动画，避免掉帧，最好离屏绘制到缓冲帧上，再通知view绘制缓冲帧。

代码实现

1. 定义一下styleable

   <declare-styleable name="MaterialLoadingProgress">
    <attr name="loadingProgress_circleRadius" format="dimension" />
    <attr name="loadingProgress_cardColor" format="color" />
    <attr name="loadingProgress_cardPadding" format="dimension" />
    <attr name="loadingProgress_strokeWidth" format="dimension" />
    <attr name="loadingProgress_strokeColor" format="color" />
    <attr name="loadingProgress_text" format="string" />
    <attr name="loadingProgress_textSize" format="dimension" />
    <attr name="loadingProgress_textColor" format="color" />
   </declare-styleable>

2. 在代码中解析styleable

   init {
     val defCircleRadius = context.resources.getDimension(R.dimen.dp24)
     val defCardColor = Color.WHITE
     val defCardPadding = context.resources.getDimension(R.dimen.dp12)
     val defStrokeWidth = context.resources.getDimension(R.dimen.dp5)
     val defStrokeColor = ContextCompat.getColor(context, R.color.teal_200)
     val defTextSize = context.resources.getDimension(R.dimen.sp14)
     val defTextColor = Color.parseColor("#333333")
     if (attrs != null) {
    val attrSet = context.resources.obtainAttributes(attrs, R.styleable.MaterialLoadingProgress)
    circleRadius = attrSet.getDimension(R.styleable.MaterialLoadingProgress_loadingProgress_circleRadius, defCircleRadius)
    cardColor = attrSet.getColor(R.styleable.MaterialLoadingProgress_loadingProgress_cardColor, defCardColor)
    cardPadding = attrSet.getDimension(R.styleable.MaterialLoadingProgress_loadingProgress_cardPadding, defCardPadding)
    strokeWidth = attrSet.getDimension(R.styleable.MaterialLoadingProgress_loadingProgress_strokeWidth, defStrokeWidth)
    strokeColor = attrSet.getColor(R.styleable.MaterialLoadingProgress_loadingProgress_strokeColor, defStrokeColor)
    text = attrSet.getString(R.styleable.MaterialLoadingProgress_loadingProgress_text) ?: ""
    textSize = attrSet.getDimension(R.styleable.MaterialLoadingProgress_loadingProgress_textSize, defTextSize)
    textColor = attrSet.getColor(R.styleable.MaterialLoadingProgress_loadingProgress_textColor, defTextColor)
    attrSet.recycle()
     } else {
    circleRadius = defCircleRadius
    cardColor = defCardColor
    cardPadding = defCardPadding
    strokeWidth = defStrokeWidth
    strokeColor = defStrokeColor
    textSize = defTextSize
    textColor = defTextColor
     }
     paint.textSize = textSize
     if (text.isNotBlank())
    textWidth = paint.measureText(text)
   }

3. 实现一个计时器，再定义一个数据类型来存储动画相关数据，还有一个动画插值器

   Timer定时器

   private fun startTimerTask() {
     val t = Timer()
     t.schedule(object : TimerTask() {
    override fun run() {
      if (taskList.isEmpty())
        return
                                                                                         
      val taskIterator = taskList.iterator()
      while (taskIterator.hasNext()) {
        val task = taskIterator.next()
                                                                                         
        task.progress += 17
        if (task.progress > task.duration) {
          task.progress = task.duration
        }
                                                                                         
        if (task.progress == task.duration) {
          if (!task.convert) {
            task.startAngle -= 40
            if (task.startAngle < 0)
              task.startAngle += 360
          }
          task.progress = 0
          task.convert = !task.convert
        }
                                                                                         
        task.progressFloat = task.progress / task.duration.toFloat()
        task.interpolatorProgress = interpolator(task.progress / task.duration.toFloat())
        task.currentAngle = (320 * task.interpolatorProgress).toInt()
        post { task.onProgress(task)  }
      }
    }
     }, 0, 16)
     timer = t
   }

   定义一个数据模型

   private data class AnimTask(
     var startAngle: Int = 0,// 扇形绘制起点
     val duration: Int = 700,// 动画时间
     var progress: Int = 0,// 动画已执行时间
     var interpolatorProgress: Float = 0f,// 插值器计算后的值，取值0.0f ～ 1.0f
     var progressFloat: Float = 0f,// 取值0.0f ～ 1.0f
     var convert: Boolean = false,// 判断扇形的绘制进程，为true时反向绘制
     var currentAngle: Int = 0,// 绘制扇形使用
     val onProgress: (AnimTask) -> Unit// 计算完当前帧数据后的回调
   )

   动画插值器

   private fun interpolator(x: Float) = x * x * (3 - 2 * 2)

4. 定义初始化缓冲帧

   此方法在外部调用显示loading时调用即可，调用前需判断是否已经初始化

   private fun initCanvas() {
     bufferBitmap = Bitmap.createBitmap(measuredWidth, measuredHeight, Bitmap.Config.ARGB_8888)
     bufferCanvas = Canvas(bufferBitmap)
   }

5. 实现扇形的绘制

   private fun drawFrame(task: AnimTask) {
     bufferBitmap.eraseColor(Color.TRANSPARENT)
                                                                                             
     val centerX = measuredWidth.shr(1)
     val centerY = measuredHeight.shr(1)
     rectF.set(
    centerX - circleRadius, centerY - circleRadius,
    centerX + circleRadius, centerY + circleRadius
     )
     paint.strokeWidth = strokeWidth
     paint.color = strokeColor
     paint.strokeCap = Paint.Cap.ROUND
     paint.style = Paint.Style.STROKE
   
     // 这里的判断，对应扇形逐渐延长、及逐渐缩短
     if (task.convert) {
    bufferCanvas.drawArc(
      rectF, task.startAngle.toFloat(), -(320.0f - task.currentAngle.toFloat()), false, paint
    )
     } else {
    bufferCanvas.drawArc(
      rectF, task.startAngle.toFloat(), task.currentAngle.toFloat(), false, paint
    )
     }
     invalidate()
   }

6. 实现扇形整体缓慢转圈

   private fun drawRotation(task: AnimTask) {
     val centerX = measuredWidth.shr(1)
     val centerY = measuredHeight.shr(1)
     bufferMatrix.reset()
     bufferMatrix.postRotate(task.progressFloat * 360f, centerX.toFloat(), centerY.toFloat())
     bufferCanvas.setMatrix(bufferMatrix)
   }

   一定要记得调用matrix#reset

否则效果就会像这样 XD：

到这里，核心功能基本就完成了。

7. 定义一个showProgress方法以及dismissProgress方法，方便外部使用

   展示

   fun showProgress() {
     if (showing)
    return
                                          
     if (!this::bufferBitmap.isInitialized) {
    initCanvas()
     }
                                          
     taskList.add(AnimTask {
    drawFrame(it)
     })
     taskList.add(AnimTask(duration = 5000) {
    drawRotation(it)
     })
     startTimerTask()
     showing = true
     visibility = VISIBLE
   }

   关闭

   fun dismissProgress() {
     if (!showing)
    return
                       
     purgeTimer()
     showing = false
     visibility = GONE
   }

最后看一下View#onDraw的实现：

override fun onDraw(canvas: Canvas) {
  val centerX = measuredWidth.shr(1)
  val centerY = measuredHeight.shr(1)
                                                                                                                         
  val rectHalfDimension = if (circleRadius > textWidth / 2f) circleRadius + cardPadding else textWidth / 2f + cardPadding
  rectF.set(
    centerX - rectHalfDimension,
    centerY - rectHalfDimension,
    centerX + rectHalfDimension,
    if (text.isNotBlank()) centerY + paint.textSize + rectHalfDimension else centerY + rectHalfDimension
  )
                                                                                                                         
  paint.color = cardColor
  paint.style = Paint.Style.FILL
  canvas.drawRoundRect(rectF, 12f, 12f, paint)
                                                                                                                         
  if (text.isNotBlank()) {
    val dx = measuredWidth.shr(1) - textWidth / 2
    paint.color = textColor
    canvas.drawText(text, dx, rectF.bottom - paint.textSize, paint)
  }
                                                                                                                         
  if (this::bufferBitmap.isInitialized)
    canvas.drawBitmap(bufferBitmap, bufferMatrix, paint)
}

源代码请移步：ARCallPlus。