如何使用可空值的AnimatedVisibility？

Question

我发现自己经常在这种情况下。在下面的示例中，我有一些类似于plates的值，我想显示/隐藏它，这取决于它是否为空。但是隐藏它总是失败的，因为当它为空时，什么都不会呈现，而动画就会变成空的虚无。

，我怎样才能使这件事成功？我希望在动画完成之前保持plates 。

    AnimatedVisibility(
        visible = plates != null,
        content = {
            if (plates != null) {
                // Render plates
            } else {
                // The animation snaps to nothingness, as opposed to animating out
            }
        })

Answer 1

这就是我最后所做的，它的工作与预期的一样！

@Composable
inline fun <T> AnimatedValueVisibility(
    value: T?,
    enter: EnterTransition = fadeIn(
        animationSpec = FloatSpec
    ) + expandVertically(
        animationSpec = SizeSpec,
        clip = false
    ),
    exit: ExitTransition = fadeOut(
        animationSpec = FloatSpec
    ) + shrinkVertically(
        animationSpec = SizeSpec,
        clip = false
    ),
    crossinline content: @Composable (T) -> Unit
) {
    val ref = remember {
        Ref<T>()
    }

    ref.value = value ?: ref.value

    AnimatedVisibility(
        visible = value != null,
        enter = enter,
        exit = exit,
        content = {
            ref.value?.let { value ->
                content(value)
            }
        }
    )
}

Answer 2

动画总是需要内容，即使没有什么可展示的。当内容为空(或为空)时，只需显示Surface：

AnimatedVisibility(
        visible = plates != null,
        content = {
            if (plates != null) {
                // Render plates
            } else {
                Surface(modifier = Modifier.fillMaxSize()) { }
            }
        })