React redux 如何使用 getState()

Question

我正在從Firebase Real-time database獲取數據並將其存儲到我的 redux 狀態中。 如何創建一個在初始調用后獲得最新狀態的操作？

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

假設函數getFromFirebase返回一個承諾，那么您可以將方法切換為異步，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getFromFirebase不是承諾，您可以通過承諾將其包裝起來：

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())
}