Android自定义View模仿即刻点赞数字切换效果实例
作者:timer
有一个项目是仿即刻的点赞,这篇文章主要给大家介绍了关于Android自定义View模仿即刻点赞数字切换效果的相关资料,文中通过示例代码介绍 的非常详细,需要的朋友可以参考下
即刻点赞展示
点赞的数字增加和减少并不是整个替换,而是差异化替换。再加上动画效果就看的很舒服。
自己如何实现这种数字切换呢?
下面用一张图来展示我的思路:
现在只需要根据这张图,写出对应的动画即可。 分为2种场景:
- 数字+1:
- 差异化的数字从3号区域由渐变动画(透明度 0- 255) + 偏移动画 (3号区域绘制文字的基线,2号区域绘制文字的基线),将数字移动到2号位置处
- 差异化的数字从2号区域由渐变动画(透明度 255- 0) + 偏移动画(2号区域绘制文字的基线,1号区域绘制文字的基线),将数字移动到1号位置处
- 数字-1
- 差异化的数字从1号区域由渐变动画(透明度 0- 255) + 偏移动画 (1号区域绘制文字的基线,2号区域绘制文字的基线),将数字移动到2号位置处
- 差异化的数字从2号区域由渐变动画(透明度 255- 0) + 偏移动画(2号区域绘制文字的基线,3号区域绘制文字的基线),将数字移动到3号位置处
公共部分就是: 不变的文字不需要做任何处理,绘制在2号区域就行。绘制差异化文字时,需要加上不变的文字的宽度就行。
效果展示
源码
class LikeView @JvmOverloads constructor( context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0 ) : View(context, attrs, defStyleAttr) { private val paint = Paint().also { it.isAntiAlias = true it.textSize = 200f } private val textRect0 = Rect(300, 100, 800, 300) private val textRect1 = Rect(300, 300, 800, 500) private val textRect2 = Rect(300, 500, 800, 700) private var nextNumberAlpha: Int = 0 set(value) { field = value invalidate() } private var currentNumberAlpha: Int = 255 set(value) { field = value invalidate() } private var offsetPercent = 0f set(value) { field = value invalidate() } private val fontMetrics: FontMetrics = paint.fontMetrics private var currentNumber = 99 private var nextNumber = 0 private var motionLess = currentNumber.toString() private var currentMotion = "" private var nextMotion = "" private val animator: ObjectAnimator by lazy { val nextNumberAlphaAnimator = PropertyValuesHolder.ofInt("nextNumberAlpha", 0, 255) val offsetPercentAnimator = PropertyValuesHolder.ofFloat("offsetPercent", 0f, 1f) val currentNumberAlphaAnimator = PropertyValuesHolder.ofInt("currentNumberAlpha", 255, 0) val animator = ObjectAnimator.ofPropertyValuesHolder( this, nextNumberAlphaAnimator, offsetPercentAnimator, currentNumberAlphaAnimator ) animator.duration = 200 animator.interpolator = DecelerateInterpolator() animator.addListener( onEnd = { currentNumber = nextNumber } ) animator } override fun onDraw(canvas: Canvas) { paint.alpha = 255 paint.color = Color.LTGRAY canvas.drawRect(textRect0, paint) paint.color = Color.RED canvas.drawRect(textRect1, paint) paint.color = Color.GREEN canvas.drawRect(textRect2, paint) paint.color = Color.BLACK if (motionLess.isNotEmpty()) { drawText(canvas, motionLess, textRect1, 0f) } if (nextMotion.isEmpty() || currentMotion.isEmpty()) { return } val textHorizontalOffset = if (motionLess.isNotEmpty()) paint.measureText(motionLess) else 0f if (nextNumber > currentNumber) { paint.alpha = currentNumberAlpha drawText(canvas, currentMotion, textRect1, textHorizontalOffset, -offsetPercent) paint.alpha = nextNumberAlpha drawText(canvas, nextMotion, textRect2, textHorizontalOffset, -offsetPercent) } else { paint.alpha = nextNumberAlpha drawText(canvas, nextMotion, textRect0, textHorizontalOffset, offsetPercent) paint.alpha = currentNumberAlpha drawText(canvas, currentMotion, textRect1, textHorizontalOffset, offsetPercent) } } private fun drawText( canvas: Canvas, text: String, rect: Rect, textHorizontalOffset: Float = 0f, offsetPercent: Float = 0f ) { canvas.drawText( text, rect.left.toFloat() + textHorizontalOffset, rect.top + (rect.bottom - rect.top) / 2f - (fontMetrics.bottom + fontMetrics.top) / 2f + offsetPercent * 200, paint ) } override fun onDetachedFromWindow() { super.onDetachedFromWindow() animator.end() } fun plus() { if (currentNumber == Int.MAX_VALUE) { return } nextNumber = currentNumber + 1 processText(findEqualsStringIndex()) if (animator.isRunning) { return } animator.start() } fun minus() { if (currentNumber == 0) { return } nextNumber = currentNumber - 1 processText(findEqualsStringIndex()) if (animator.isRunning) { return } animator.start() } private fun findEqualsStringIndex(): Int { var equalIndex = -1 val nextNumberStr = nextNumber.toString() val currentNumberStr = currentNumber.toString() val endIndex = min(currentNumberStr.length, nextNumberStr.length) - 1 for (index in 0..endIndex) { if (nextNumberStr[index] != currentNumberStr[index]) { break } equalIndex = index } return equalIndex } private fun processText(index: Int) { val currentNumberStr = currentNumber.toString() val nextNumberStr = nextNumber.toString() if (index == -1) { motionLess = "" currentMotion = currentNumberStr nextMotion = nextNumberStr } else { motionLess = currentNumberStr.substring(0, index + 1) currentMotion = currentNumberStr.substring(index + 1) nextMotion = nextNumberStr.substring(index + 1) } } }
总结
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