Question

为什么不能使用var值更改来复制数据类对象？

data class AppState(var list: List<Image> = ArrayList<Image>(),
                val uiState: UIState = UIState.LIST,
                val isFetching: Boolean = false)

...

val list = state!!.list.sublist(0,1);
state.copy(list = list)        // No change
state.copy(isFetching = true)  // Works like a charm

Answer 1

copy方法不会改变原始对象。它返回一个具有更改值的新对象。我尝试了您的示例，当我在新的val中捕获返回的对象时，两个副本都按预期工作：

val list = state!!.list.subList(0,1)

// Creates a new object with the new list.
val withNewList = state.copy(list = list)

// Creates a new object with the new isFetching.
val withNewIsFetching = withNewList.copy(isFetching = true)

如果要改变state - 对象的列表值，可以这样做：

val list = state!!.list.subList(0,1)
state.list = list

具有更改的var值的Kotlin数据类副本

1 个答案: