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

Posted 2022-03-25 anyRTC

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。