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

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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

    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
    ```Kotlin
    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
    )
  4. 定义初始化缓冲帧
  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)
    

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

    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)

源代码请移步:ARCallPlus

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