Javascript 对象/地理位置 API

Posted 2023-02-23

【中文标题】Javascript 对象/地理位置 API

【英文标题】：Javascript Objects / Geolocation API

【发布时间】：2012-04-12 05:55:25

【问题描述】：

我正在使用 Phonegap 开发一个使用 Geolocation 的移动应用程序。我之前使用过 Geolocation，但这次我认为为它创建一个新的对象包装器会更好，因为大部分功能都基于此，并且不想以混乱的代码结束。

解决方案可能是直截了当的，但它打败了我，因为我从来没有在 JS 中使用对象做过任何非常高级的事情。这是目前的代码（删除了不需要的部分）：

function Geolocation(maximumAge, accurate) 
    this.settings = 
            'maximumAge': maximumAge,
            'accurate': accurate
    


Geolocation.prototype = 
    position: 
        latitude: null,
        longitude: null,
        altitude: null,
        accuracy: null,
        altitudeAccuracy: null,
        heading: null,
        speed: null
    ,
    lastCheck: null,
    watchId: null,
    onSuccess: function(position) 
        this.position.latitude = position.coords.latitude;
        this.position.longitude = position.coords.longitude;
        this.position.altitude = position.coords.altitude;
        this.position.accuracy = position.coords.accuracy;
        this.position.altitudeAccuracy = position.coords.altitudeAccuracy;
        this.position.heading = position.coords.heading;
        this.position.speed = position.coords.speed;
        this.lastCheck = new Date(position.timestamp);
    , 
    onError: function(error) 
        console.log(error.code+' '+error.message);
    ,
    getCoordinates: function() 
        if (this.watchId == null)  
            this.watchId = navigator.geolocation.watchPosition(this.onSuccess, this.onError,  maximumAge: this.settings.maximumAge, enableHighAccuracy: this.settings.accurate);
        
        return 
            latitude: this.position.latitude,
            longitude: this.position.longitude
        ;
    
;

您可能已经注意到，当我调用 getCoordinates() 时，回调成功函数（我猜）超出了对象的范围，因此不知道“this”是什么......知道如何解决这个问题或正确的实现是什么？

感谢您的宝贵时间！

稍后编辑：我知道我需要修改函数以仅在找到位置后返回坐标。目前不确定如何执行此操作，但如果您有任何提示，那就太好了！

【参考方案1】：

好的，我想通了，部分是在其他线程关于绑定回调函数范围的帮助下：javascript Callback Scope

为了返回坐标，我使用了回调函数。包括下面的代码，我将其标记为社区 wiki - 但如果有人有任何建议，请继续提出。一切似乎都运行良好，但也许我在这里没有做某事。

function Geolocation(maximumAge, accurate) 
    this.settings = 
            'maximumAge': maximumAge,
            'accurate': accurate
    


Geolocation.prototype = 
    position: 
        latitude: null,
        longitude: null,
        altitude: null,
        accuracy: null,
        altitudeAccuracy: null,
        heading: null,
        speed: null
    ,
    lastCheck: null,
    callback: null,
    watchId: null,
    onSuccess: function(position) 
        this.position.latitude = position.coords.latitude;
        this.position.longitude = position.coords.longitude;
        this.position.altitude = position.coords.altitude;
        this.position.accuracy = position.coords.accuracy;
        this.position.altitudeAccuracy = position.coords.altitudeAccuracy;
        this.position.heading = position.coords.heading;
        this.position.speed = position.coords.speed;
        this.lastCheck = new Date(position.timestamp);

        var pos = 
            latitude: this.position.latitude,
            longitude: this.position.longitude
        ;
                // call callback with position and accuracy parameters
        this.callback(pos, this.position.accuracy);
    , 
    onError: function(error) 
        console.log(error.code+' '+error.message);
    ,
    getCoordinates: function(callback) 
                // Helper function to bind scope to callback function as seen at https://***.com/questions/183214/javascript-callback-scope
        function bind(scope, fn) 
            return function () 
                fn.apply(scope, arguments);
            ;
        
                // Assign the callback function to the local member
        this.callback = callback;
                // watchPosition is a method that gets called each time the position changes. Making sure it's only getting called once (watchId can be used to stop the function when necessary
        if (this.watchId == null) 
                        // notice usage of the bind function here 
            this.watchId = navigator.geolocation.watchPosition(bind(this, this.onSuccess), bind(this, this.onError),  maximumAge: this.settings.maximumAge, enableHighAccuracy: this.settings.accurate);
        
    
;

使用示例：

var geo = new Geolocation(3000, true);
geo.getCoordinates(createMap);

function createMap(position, accuracy) 
    // Your code here