Question

当我运行此功能时，在Ionic4应用程序（带有Angular 7和Typescript 3）中：

  public addDeviceMarkers(devicePositions: Array<any>): void {
    devicePositions.map(function(device) {
      const position = {lat: device.latitude, lng: device.longitude};
      const marker = new google.maps.Marker({
        position: position,
        title: device.deviceId
      });
      marker.setMap(this.map);
    });
  }

我遇到此错误：

core.js:15724 ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'map' of undefined
TypeError: Cannot read property 'map' of undefined
    at google-map.component.ts:214

我已经解决了问题，以这种方式修改了功能：

  public addDeviceMarkers(devicePositions: Array<any>): void {
    const mapObject = this.map;
    devicePositions.map(function(device) {
      const position = {lat: device.latitude, lng: device.longitude};
      const marker = new google.maps.Marker({
        position: position,
        title: device.deviceId
      });
      marker.setMap(mapObject);
    });
  }

我必须定义const mapObject = this.map;。问题是，为什么进入映射循环this是未定义的？

Answer 1

您无需声明即可实现

const mapObject = this.map;

public addDeviceMarkers(devicePositions: Array<any>): void {
    var selfRef = this;
    devicePositions.map(function(device) {
      const position = {lat: device.latitude, lng: device.longitude};
      const marker = new google.maps.Marker({
        position: position,
        title: device.deviceId
      });
      marker.setMap(selfRef.map);
    });
  }

为什么在映射循环中得到“ TypeError：无法读取未定义的属性”？

1 个答案: