【Compose 错误使用rememberSaveable导致java.lang.IllegalArgumentException: Failed requirement问题解决记录】

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文章介绍了在AndroidJetpackCompose中遇到的一个错误，即由于使用rememberSaveable保存自定义的密封类对象导致的IllegalArgumentException。分析了rememberSaveable的工作原理，指出其依赖于onSaveInstanceState，因此保存的数据必须是可序列化的，如Bundle支持的基本数据类型或Parcelable。为解决问题，作者修改了密封类，添加了一个整型code参数，并在Saver中根据code保存和恢复状态。这样，应用可以正确地保存和恢复LoadingButtonState的状态了。

Compose 错误使用rememberSaveable导致java.lang.IllegalArgumentException: Failed requirement问题解决记录

先看报错信息

异常堆栈：

E  FATAL EXCEPTION: main
Process: com.lie.composeanimationkit, PID: 8609
java.lang.IllegalArgumentException: Failed requirement.
at androidx.compose.runtime.saveable.ListSaverKt$listSaver$1.invoke(ListSaver.kt:39)
at androidx.compose.runtime.saveable.ListSaverKt$listSaver$1.invoke(ListSaver.kt:33)
at androidx.compose.runtime.saveable.SaverKt$Saver$1.save(Saver.kt:66)
at androidx.compose.runtime.saveable.RememberSaveableKt$rememberSaveable$1$valueProvider$1.invoke(RememberSaveable.kt:100)
at androidx.compose.runtime.saveable.RememberSaveableKt$rememberSaveable$1.invoke(RememberSaveable.kt:102)
at androidx.compose.runtime.saveable.RememberSaveableKt$rememberSaveable$1.invoke(RememberSaveable.kt:98)
at androidx.compose.runtime.DisposableEffectImpl.onRemembered(Effects.kt:81)
at androidx.compose.runtime.CompositionImpl$RememberEventDispatcher.dispatchRememberObservers(Composition.kt:802)
at ...

定位到代码处：

@Composable
fun rememberLoadingButtonState(
    initialState: LoadingState = LoadingState.Ready,
): LoadingButtonState = rememberSaveable(saver = LoadingButtonState.Saver) {
    LoadingButtonState(initialState)
}

这里我定义了一个rememberLoadingButtonState方法，调用rememberSaveable来记录按钮的状态，

LoadingState是我定义的一个密封类，对应各种状态

sealed class LoadingState {
    object Ready : LoadingState()
    object Loading : LoadingState()
    object Success : LoadingState()
    object Error : LoadingState()
}

LoadingButtonState是状态的持有者，同时内部实现了Saver 来存储和读取状态

class LoadingButtonState(val currentState: LoadingState = LoadingState.Ready) {

    companion object {
        /**
         * The default [Saver] implementation for [PagerState].
         */
        val Saver: Saver<LoadingButtonState, *> = listSaver(
            save = {
                listOf<Any>(
                    it.currentState,
                )
            },
            restore = {
                LoadingButtonState(
                    currentState = it[0] as LoadingState,
                )
            }
        )
    }
}

问题原因：

定位到Saver类，看Saver的说明信息：

The Saver describes how the object of Original class can be simplified and converted into something which is Saveable.
What types can be saved is defined by SaveableStateRegistry, by default everything which can be stored in the Bundle class can be saved. The implementations can check that the provided value can be saved via SaverScope.canBeSaved
You can pass the implementations of this class as a parameter for rememberSaveable.

因为rememberSaveable实际是基于onSaveInstanceState实现的，具体可以看fundroid大佬的这篇文章：
Compose状态保存rememberSaveable原理解析

因此同样，Saver存储和读取的数据必须是能写进Bundle的基本数据类型或者Parcle，具体可以用SaverScope.canBeSaved()方法判断是否支持存储

了解问题原因之后就好办了，上面的代码中，Saver存储的是自定义的密封类对象，所以不支持Saver.save方法，那我们就改一下：

sealed class LoadingState(val code: Int) {
    object Ready : LoadingState(0)
    object Loading : LoadingState(1)
    object Success : LoadingState(2)
    object Error : LoadingState(3)

    companion object {
        fun getState(code: Int): LoadingState {
            return when (code) {
                0 -> Ready
                1 -> Loading
                2 -> Success
                else -> Error
            }
        }
    }
}

为了避免太大的改动，继续保留密封类的正常使用，可以参考这么去改LoadingState密封类：

密封类的构造方法中添加一个基本数据类型参数code，注意前面要有val，不然不是类的成员属性，而只单纯作为构造参数的话，是无法读取的
密封类添加静态方法，根据code返回对应的密封类对象

思路其实类似与emun枚举类的getValue()方法

然后Saver处也要调整一下存储和写入的规则：

class LoadingButtonState(val currentState: LoadingState = LoadingState.Ready) {

    companion object {
        /**
         * The default [Saver] implementation for [PagerState].
         */
        val Saver: Saver<LoadingButtonState, *> = listSaver(
            save = {
                listOf<Any>(
                    it.currentState.code,	//改为取基本数据类型code，存储
                )
            },
            restore = {
                LoadingButtonState(
                    currentState = LoadingState.getState(it[0] as Int),	//根据code获取对应的密封类对象
                )
            }
        )
    }
}