React redux 如何使用 getState()

Question

我正在从 Firebase Real-time database 中获取数据并将其存储到我的 redux 状态中。我如何创建一个操作，在初始调用后获得最新和最新的状态？

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

假设函数 getFromFirebase returns 是一个 promise，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 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())
}

React redux 如何使用 getState()

React redux how to use getState()

javascript

reactjs

redux

redux-thunk

react-redux