安卓JetpackCompose中的共享元素是如何工作的？

共享元素是通过在Compose中使用Transition API实现的。该API在为不同元素提供进出动画时非常有用。在联合使用Transition和NavigationView时，可以使用rememberNavController()函数来创建导航控制器，然后定义转换。在转换中，将SharedAxis对象分配给目标和源。下面是一个示例代码：

val navController = rememberNavController()
val transition = updateTransition(navController, label = "nav")
val toDown = SharedAxis(
    motionSpec = TweenSpec(durationMillis = 300)
)
val toUp = SharedAxis(
    motionSpec = TweenSpec(durationMillis = 300),
    direction = SharedAxis.Y
)
val backstackEntry = navController.currentBackStackEntryAsState()
val destination = backstackEntry.value?.destination?.route
// 定义转换和源
val triggerBackwardAnimation = destination?.let {
    transition.animate(direction = "forward$it") { 
        if (it == "secondScreen") toDown else toUp
    }
}
// 定义目标
val triggerForwardAnimation = destination?.let {
    transition.animate(direction = "backward$it") {
        if (it == "secondScreen") toUp else toDown
    }
}
// 使用共享元素
NavHost(navController = navController, startDestination = "firstScreen") {
    composable("firstScreen") {
        FirstScreen(
            onClick = { route -> navController.navigate(route) },
            triggerBackwardAnimation = triggerBackwardAnimation
        )
    }
    composable("secondScreen") {
        SecondScreen(triggerForwardAnimation = triggerForwardAnimation)
    }
}

此示例中，我们为向前和向后导航定义了两种共享元素。界面之间的动画可以根据界面之间的关系切换。这是仅处理带有Jetpack Compose的动画的一种方法。