Question

我试图从Firebase中提取很多变量。并非所有这些都有任何内容。因此，我需要能够处理nil并同时转换为所需的数据类型（例如，Float和Int）

目前我在第一个Float“距离”上遇到错误：

“主题1：致命错误：在解开可选值时意外发现nil

几个问题：

如何使Float转换处理潜在的无案例
我想将Float存储为Firebase中的字符串，而不是将其包装在NSNumber中。你同意吗？
如果在应用程序中我只需要例如。以下5个变量，我是否应该对此进行特定查询 - 或者通常不需要花费很多成本来获取所有变量？
我是否正确制作了数组或地图（字典）元素（例如，like，comments，imageURL）？

代码：

    // Get data on all activities
    func getAllFeedActivities(handler: @escaping (_ activities: [Activity]) -> (Void)) {
        var activityArray = [Activity]()        


        REF_ACTIVITY.observeSingleEvent(of: .value) { (feedActivitySnapshot) in

            guard let feedActivitySnapshot = feedActivitySnapshot.children.allObjects as? [DataSnapshot] else { return }


            for activity in feedActivitySnapshot {

                let activityId =            activity.key as String
                let name =                  activity.childSnapshot(forPath: "name").value as? String ?? ""
                let description =           activity.childSnapshot(forPath: "description").value as? String ?? ""

                let userId =                activity.childSnapshot(forPath: "userId").value as? String ?? ""
                let type =                  activity.childSnapshot(forPath: "type").value as? String ?? ""
                let gearId =                activity.childSnapshot(forPath: "gearId").value as? String ?? ""

                let distance =              Float(activity.childSnapshot(forPath: "distance").value as? String ?? "") as! Float                          // In meters
                let totalElevationGain =    Float(activity.childSnapshot(forPath: "totalElevationGain").value as? String ?? "") as! Float                // In meters
                let elevationHigh =         Float(activity.childSnapshot(forPath: "elevationHigh").value as? String ?? "") as! Float                     // In meters                         
                let elevationLow =          Float(activity.childSnapshot(forPath: "elevationLow").value as? String ?? "") as! Float                      // In meters

                let startTime =             activity.childSnapshot(forPath: "startTime").value as? String ?? ""                                          // Unix time - seconds
                let timeZone =              activity.childSnapshot(forPath: "timeZone").value as? String ?? ""
                let movingTime =            Int(activity.childSnapshot(forPath: "movingTime").value as? String ?? "") as! Int                            // In seconds
                let elapsedTime =           Int(activity.childSnapshot(forPath: "elapsedTime").value as? String ?? "") as! Int                           // In seconds


                let likeCount =             Int(activity.childSnapshot(forPath: "likeCount").value as? String ?? "") as! Int
                let likes =                 activity.childSnapshot(forPath: "likes").value as? NSArray ?? [""]
                let commentCount =          Int(activity.childSnapshot(forPath: "commentCount").value as? String ?? "") as! Int
                let comments =              activity.childSnapshot(forPath: "comments").value as? NSArray ?? [""]
                let imageCount =            Int(activity.childSnapshot(forPath: "imageCount").value as? String ?? "") as! Int
                let imageURLs =             activity.childSnapshot(forPath: "imageURLs").value as? NSArray ?? [""]
                let defaultImageURL =       activity.childSnapshot(forPath: "defaultImageURL").value as? String ?? ""

                let activity = Activity(activityId: activityId, name: name, description: description, userId: userId, type: type, gearId: gearId, distance: distance, totalElevationGain: totalElevationGain, elevationHigh: elevationHigh, elevationLow: elevationLow, startTime: startTime, timeZone: timeZone, movingTime: movingTime, elapsedTime: elapsedTime, likeCount: likeCount, likes: likes as! Array<String>, commentCount: commentCount, comments: comments as! Array<String>, imageCount: imageCount, imageURLs: imageURLs as! [String], defaultImageURL: defaultImageURL)
                activityArray.append(activity)
            }
            handler(activityArray)
        }
    }

Answer 1

1）如果要分配默认值，则该值应为

String使用.value as? String ?? ""
Int使用.value as? Int ?? 0
Float使用.value as? Float ?? 0.0
Double使用.value as? Double ?? 0.0
Bool使用.value as? Bool ?? false
Array使用.value as? [String] ?? [] //其中String必须是预期的数据类型
Dictionary使用.value as? [String:Any] ?? [:]

如果是Array和Dictionary，则必须在未声明之前注释该类型

let imageURLs : [String] = ...

但是我建议使用数据库中已有的默认值声明属性，然后值永远不会为nil，您可以强制解包它们。

您的其他问题的答案：

2）不，始终使用合适的类型。

3）是的，一个特定的查询更有效，总是处理所有值更昂贵。

4）参见1） - 不要在Swift中使用NSArray / NSDictionary。

复杂的firebase读取查询 - String，Float，Int和NSArray

1 个答案: