GeoFire不会返回任何结果

Question

我遇到了GeoFire的问题。

首先，根据Geofire github页面上的文档，我无法安装cocoapod。搜索之后，我发现设置podfile的正确方法是：

    pod 'GeoFire', :git => 'https://github.com/firebase/geofire-objc.git'

不确定是否有任何代码无法正常工作，但以下情况不起作用：

    if  let geoFire = GeoFire(firebaseRef: self.firebaseRef) {

 //this is an exact match to an item in the database, there are others nearby as well
        let center = CLLocation(latitude: 40.72946918822954, longitude: -73.9883231047775)

        guard let circleQuery = geoFire.query(at: center, withRadius: 5) else {
            return
        }

        var results = [String]()

        circleQuery.observe(.keyEntered, with: { (key, location) in
            if let result = key {
               results.append(result)
            }
        })

        circleQuery.observeReady({ 
            print("ALL ARE LOADED: \(results)")
            circleQuery.removeAllObservers()
        })

以下代码没有结果。知道为什么吗？