React redux 如何使用 getState()

Question

我正在从中获取数据Firebase Real-time database并将其存储到我的 redux 状态中。我如何创建一个在初始调用后获得最新状态的操作？const getIds = (state) => state.notes.activeNotes;export const getUserNotes = (currentUserId) => (dispatch, getState) => {  getFromFirebase(`/Notes/${currentUserId}/`, (response) => {    var ids = Object.keys(response)      dispatch(setNoteIds(ids)); //should dispatch ids something like this [1,2,3,4,5]  })  const test= getIds(getState());  console.log(test); //current output []}Expected output: [1,2,3,4,5]Actual output: []

Answer 1

假设该函数getFromFirebase返回一个承诺，那么您可以将方法切换为异步，如下所示：

export const getUserNotes = (currentUserId) => async (dispatch, getState) => {

  // wait the result dispatched

  await getFromFirebase(`/Notes/${currentUserId}/`, (response) => {

    var ids = Object.keys(response)

      dispatch(setNoteIds(ids)); //should dispatch ids something like this [1,2,3,4,5]

  })

  

  const test= getIds(getState());

}

或者如果这getFromFirebase不是一个承诺，你可以用一个承诺来包装它：

export const getUserNotes = (currentUserId) => async (dispatch, getState) => {

  // wrap in a promise

  await new Promise(resolve => {

    getFromFirebase(`/Notes/${currentUserId}/`, (response) => {

      var ids = Object.keys(response)

        dispatch(setNoteIds(ids)); //should dispatch ids something like this [1,2,3,4,5]

        resolve();

    })

  })

  

  const test= getIds(getState())

}