Question

我正在构建一个旅行应用程序。该应用程序中的屏幕之一是地图屏幕。我使用Expo Locations中的watchPositionAsync。 watchPositionAsync可以很好地运行并传递用户坐标。我希望watchPositionAsync在“地图”屏幕/模块关闭后停止/删除。我将.remove（）函数附加到watchPositionAsync，但是不幸的是watchPositionAsync继续运行。模态关闭后，如何使其停止运行？

我尝试以各种不同方式使用.remove（）： -componentWillUnmount等。 -我什至尝试在按钮（onPress）中执行它

async componentWillMount() {

    const { status } = await Permissions.askAsync(Permissions.LOCATION);

    if (status === 'granted') {
      this._getLocationAsync();
    } else {
      this.setState({ error: 'Locations services needed' });
    }
  }

  componentWillUnmount() {
      this._stopGetLocationAsync().catch(err => console.log('err'));
  }

  _getLocationAsync = async () => {
      const location = await Location.watchPositionAsync(
          {
              enableHighAccuracy: true,
              distanceInterval: 1,
              timeInterval: 10000
          },
          newLocation => {
              let coords = newLocation.coords;
          // this.props.getMyLocation sets my reducer state my_location
          this.props.getMyLocation({
              latitude: parseFloat(coords.latitude),
              longitude: parseFloat(coords.longitude)
          });
        },
        error => console.log(error)
      );
      return location;
  };

  _stopGetLocationAsync = async () => {
    const location = await Location.watchPositionAsync();
    return location.remove();
  };

我期望在卸载组件后将watchPositionAsync删除，但是当我console.log（location.remove（））时，我变得不确定。

Answer 1

在您的_stopGetLocationAsync中，您将创建一个新的watchPositionAsync承诺对象并将其删除。因此，_getPositionASync中的原始地址仍然存在。

您需要将const Location更改为类变量i.e. this.location=...，然后将remove方法传递给该变量。

这是修改后的代码

async componentWillMount() {

    const { status } = await Permissions.askAsync(Permissions.LOCATION);

    if (status === 'granted') {
      this._getLocationAsync();
    } else {
      this.setState({ error: 'Locations services needed' });
    }
  }

  componentWillUnmount() {
     this.location.remove(callback...);
  }

  _getLocationAsync = async () => {
      this.location = await Location.watchPositionAsync(
          {
              enableHighAccuracy: true,
              distanceInterval: 1,
              timeInterval: 10000
          },
          newLocation => {
              let coords = newLocation.coords;
          // this.props.getMyLocation sets my reducer state my_location
          this.props.getMyLocation({
              latitude: parseFloat(coords.latitude),
              longitude: parseFloat(coords.longitude)
          });
        },
        error => console.log(error)
      );
      return location;
  };

世博会的Locations.watchPositionAsync未删除

1 个答案: