Redux还原器动态返回以前的状态

Question

我有一个Redux Reducer，每次用户选择新选项时，它都需要存储以前选择的选项。

• 用户选择A(返回空数组(
• 用户选择B(返回A(
• 用户选择C(返回B(
• 用户选择D(返回C(

。

export default function reducer(state = [], action) {
switch (action.type) {
case previousSelectionAction.PREVIOUS_SELECTION: {
// Need to return the previous selection
// Have tried:
//  return [...state] and other variations with action.payload and dropping item in array
// but this just returns the same state, does not update each tie a user selects a new option
}
default:
return state;

}}

Answer 1

当选择发生变化时，将上一个值存储在不同的状态属性中：

case updateSelection:
return {
...state,
previous: state.current,
current: action.payload
}

然后您可以选择以前的值。

Answer 2

与其将状态设为单个对象，不如将其设为两个对象，一个存储上一个值，另一个存储当前值。

逻辑如下：

initialState = { previous: {}, current: {}}
Case updateSelection: 
return {
...state, 
previous: state.current, 
current: action.payload
}

然后，您可以在代码中检查state.previous。