Android中分析Jetpack Compose动画内部的实现原理

var isOffset by remember { mutableStateOf(false) }
val offsetAnimation by animateDpAsState(targetValue = if (isOffset) 100.dp else 0.dp)
Button(
    onClick = { isOffset = !isOffset },
    modifier = Modifier.offset(0.dp, offsetAnimation)
) {
    Text(text = "点我进行位移")
}

var isOffset by remember { mutableStateOf(false) }
val offsetAnimation by animateDpAsState(targetValue = if (isOffset) 100.dp else 0.dp)
Button(
    onClick = { isOffset = !isOffset },
    modifier = Modifier.offset(0.dp, offsetAnimation)
) {
    Text(text = "点我进行位移")
}

    /**
     * creator: lt
     * effect : 自定义的动画播放器,逻辑更简单
     * warning:
     * [initialValueWithState]动画要改变的状态,起始动画值为其value值
     * [targetValue]要通过动画转化到的目标值
     * [duration]动画的持续时间
     */
    @OptIn(ExperimentalComposeApi::class)
    suspend fun animateWithFloat(
        initialValueWithState: MutableState<Float>,
        targetValue: Float,
        duration: Int = AnimationConstants.DefaultDurationMillis,
    ) {
        //动画起始值,目标差值
        val startValue = initialValueWithState.value
        val valueToBeTransformed = targetValue - startValue
        //动画起始时间,持续时间
        val startTime = System.nanoTime()
        val duration = duration * 1000000L
        //通过循环在下一帧计算动画的值
        val frameClock = coroutineContext.monotonicFrameClock
        while (System.nanoTime() <= startTime + duration) {
            frameClock.withFrameNanos {
                //计算动画的值,并设置值给状态
                val progress = minOf(it - startTime, duration).toFloat() / duration
                val increase = progress * valueToBeTransformed
                initialValueWithState.value = startValue + increase
            }
        }
    }