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

程序猿一东
182 阅读3分钟

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)

  1. 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)
}

  1. 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()
}

  2. 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。

  1. 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

Kotlin
  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)
}
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