javascript - 如何进行多个 Promise 调用

Question

您好，我必须进行多个 Promise 调用，但我陷入困境，基本上我从通过 modbus/TCP 通信的套接字服务获取数据。我能够通过 cordova 插件进行通信，但我在掌握 Promise 的工作原理时遇到一些问题，这里有一些代码:

    ngOnInit() {
    console.log('init')
    this.getRegistrationNumber().then(() => {
      this.swVersionRequest()
    })    
  }

  getRegistrationNumber() {
    let self = this
    return new Promise(function(resolve, reject) {
      self.socketService.getMatricola().then((data) => {
        self.registrationNumber = self.socketService.arrayBuffer2str(data.data.slice(3, data.data.length-2))
        console.log(`Registration number is ${self.registrationNumber}`)
        resolve()
      })
      .catch(error => {
        reject(error)
      })
    })
  }

  swVersionRequest() {
    console.log("software version request");
      this.socketService.getSwVersion().then((data) => {
        this.softwareVersionWifiGsm = this.socketService.arrayBuffer2str(data.data.slice(3, data.data.length-2))
        this.softwareVersionWifiGsm = this.softwareVersionWifiGsm.substring(0, 2).split('').join(".") + ' ' + this.transformSwVersion(this.softwareVersionWifiGsm.substring(2, this.softwareVersionWifiGsm.length))
        console.log(`Software version is ${this.softwareVersionWifiGsm}`)
      })
  }

  getMachineType() {
    console.log('get machine type')
    this.socketService.getMachineType().then((data) => {
      this.machineType = data.data.slice(4, data.data.length-2)
      console.log(`Machine type is ${this.machineType}`)
    })
  }

  refreshData() {    
    this.getRegistrationNumber().then(() => {
      this.swVersionRequest()
    })
    .then(() => { // not working like this
      this.getMachineType()
    })
  }

  transformSwVersion(str) {
    return str.replace(/(\d\d)(\d\d)(\d\d)/, "$1/$2/$3")
  }

然后，当我获得 machineType 时，我想检查 Promise 的响应，如下所示:

if (this.machineType == 2) {
   callSoftwareVersionB() // another promise
} else {
   callSoftwareVersionC() // another promise
}

不知道说清楚了没有

提前谢谢

Answer 1

我不明白你的所有问题，但你的问题似乎只与 promise 有关。

如果你想链接你的 Promise，你必须返回解析*(在这里包含你的数据*)，如下所示:

return new Promise(function(resolve, reject) {
  return self.socketService.getMatricola().then((data) => {
    self.registrationNumber = self.socketService.arrayBuffer2str(data.data.slice(3, data.data.length-2))
    console.log(`Registration number is ${self.registrationNumber}`)
    return resolve(withYourDataHere)
  })

之后，您将能够链接您的 Promise 并得到如下结果:

getRegistrationNumber().then((yourData) => {
  console.log(yourData);
  return yourData;
});

如果不需要之前的响应来执行下一个请求，则可以执行 Promise.all()。

例如，您可以这样做:

const promises = [];
promises.push(getRegistrationNumber());
promises.push(getMachineType());
//etc...
return Promise.all(promises).then(() => {
  //your code will be executed after all your requests are resolved
})

就您而言:

refreshData() {    
   this.getRegistrationNumber().then(() => {
     this.swVersionRequest()
   })
   .then(() => { // not working like this
     this.getMachineType()
   })
 }

此代码变为:

swVersionRequest() {
    console.log("software version request");
      return this.socketService.getSwVersion().then((data) => {
        this.softwareVersionWifiGsm = this.socketService.arrayBuffer2str(data.data.slice(3, data.data.length-2))
        this.softwareVersionWifiGsm = this.softwareVersionWifiGsm.substring(0, 2).split('').join(".") + ' ' + this.transformSwVersion(this.softwareVersionWifiGsm.substring(2, this.softwareVersionWifiGsm.length))
        console.log(`Software version is ${this.softwareVersionWifiGsm}`)
      })
}

getMachineType() {
    console.log('get machine type')
    return this.socketService.getMachineType().then((data) => {
      console.log(`Machine type is ${this.machineType}`)
      return this.machineType = data.data.slice(4, data.data.length-2)
    })
}

refreshData() {    
   return this.getRegistrationNumber().then(() => {
     return this.swVersionRequest().then(() => {
       return this.getMachineType() //you can chain that if you change the return in your function
     })
   })
}

或者

refreshData() {  
      const promises = [];
      promises.push(this.getRegistrationNumber());
      promises.push(this.swVersionRequest());
      promises.push(this.getMachineType());
      return Promise.all(promises).then(() => {
         //type your code here
      })
    }

我同意 saglamcem 的观点，您在 MDN 上拥有执行此操作所需的所有文档，并且您也可以使用 Observables。

希望我们能帮助您。