Android技術分享|【自定義View】實現Material Design的Loading效果_anyRTC

預期效果

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實現思路

分析一下這個動畫，效果應該是通過兩個動畫來實現的。 * 一個不停變速伸縮的扇形動畫 * 一個固定速度的旋轉動畫

扇形可以通過canvas#drawArc來實現

旋轉動畫可以用setMatrix實現

圓角背景可以通過canvas#drawRoundRect實現

還需要一個計時器來實現動畫效果

這個View最好能夠更方便的修改樣式，所以需要定義一個declare-styleable，方便通過佈局來修改屬性。這些元素應該包括： * 最底層的卡片顏色 * 卡片內變局 * 內部長條的顏色 * 長條的粗細 * 長條的距離中心的半徑 * 字型大小 * 字型顏色

因為用到動畫，避免掉幀，最好離屏繪製到緩衝幀上，再通知view繪製緩衝幀。

程式碼實現

定義一下styleable xml <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>
在程式碼中解析styleable Kotlin 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) }
實現一個計時器，再定義一個數據型別來儲存動畫相關資料，還有一個動畫插值器

Timer定時器 ```Kotlin 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 } ```

定義一個數據模型 Kotlin private data class AnimTask( var startAngle: Int = 0,// 扇形繪製起點 val duration: Int = 700,// 動畫時間 var progress: Int = 0,// 動畫已執行時間 var interpolatorProgress: Float = 0f,// 插值器計算後的值，取值0.0f ～ 1.0f var progressFloat: Float = 0f,// 取值0.0f ～ 1.0f var convert: Boolean = false,// 判斷扇形的繪製程序，為true時反向繪製 var currentAngle: Int = 0,// 繪製扇形使用 val onProgress: (AnimTask) -> Unit// 計算完當前幀資料後的回撥 ) 動畫插值器 Kotlin private fun interpolator(x: Float) = x * x * (3 - 2 * 2) 4. 定義初始化緩衝幀此方法在外部呼叫顯示loading時呼叫即可，呼叫前需判斷是否已經初始化 Kotlin private fun initCanvas() { bufferBitmap = Bitmap.createBitmap(measuredWidth, measuredHeight, Bitmap.Config.ARGB_8888) bufferCanvas = Canvas(bufferBitmap) } 5. 實現扇形的繪製 ```Kotlin 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

// 這裡的判斷，對應扇形逐漸延長、及逐漸縮短 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. 實現扇形整體緩慢轉圈Kotlin 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) } ```

一定要記得呼叫matrix#reset

否則效果就會像這樣 XD：

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到這裡，核心功能基本就完成了。

定義一個showProgress方法以及dismissProgress方法，方便外部使用

展示 ```Kotlin 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 } ```

關閉 ```Kotlin fun dismissProgress() { if (!showing) return

purgeTimer() showing = false visibility = GONE } ```

最後看一下View#onDraw的實現： ```Kotlin 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) } ```

原始碼請移步：ARCallPlus。

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