javascript - Ionic 2内部函数和外部函数

Question

我目前正在使用 BLE https://github.com/evothings/cordova-ble 库使用 Ionic 2 开发应用程序。我在这里想知道的是，我有一个函数 connectToDevice ，它调用函数 ble.connectToDevice ，而函数 ble.connectToDevice 又调用函数 onConnected 。在函数 onConnected 内部，我想调用函数 connectToDevice 外部的函数 enableNotification(device)。但我收到错误:TypeError: _this.enableCoinNotification is not a function.

有人可以解决这个问题并向我解释一下吗？

export class BleProvider {
 constructor(){
  this.connectToDevice(device)
 }

 connectToDevice(device){
   let onConnected = (device) => {
    console.log("Connected to device: " + device.name);
    return startNotifications(device);
  },
  onDisconnected = (device) => {
    console.log('Disconnected from device: ' + device.name);
  },
  onConnectError = (error) => {
    console.log('Connect error: ' + error);
  };

setTimeout(() => {
  ble.connectToDevice(
    device,
    onConnected,
    onDisconnected,
    onConnectError)
  }, 500);

  let startNotifications = (device) => {
    console.log("Start Notification called");
    this.enableCoinNotification(device) // ERROR : TypeError: _this.enableCoinNotification is not a function
  };
 }

  enableCoinNotification(device){

   let onNotificationSuccess = (data) =>{
    console.log('characteristic data: ' + ble.fromUtf8(data));
   },
   onNotificationError = (error) =>{
   };
  ble.enableNotification(
   device,
   this.coinEventNotificationUUID,
   onNotificationSuccess,
   onNotificationError)
   }
}

Answer 1

添加bind API:

  let startNotifications = (device) => {
    console.log("Start Notification called");
    this.enableCoinNotification(device);
  };
  startNotifications.bind(this); // <-- Add this line

当您仅传递由箭头函数定义的函数定义时，this 将会丢失。

<小时/>

或者:

是的，我同意@Junior

ble.connectToDevice(device,
   (...arg) => onConnected(...arg),
   (...arg) => onDisconnected(...arg),
   (...arg) => onConnectError(...arg));

通过更改箭头函数的回调，您可以引用父 this 对象范围。