Question

我在使用以下代码时遇到一些问题，为什么它不起作用的任何想法？

guard let parsedData = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments),
    let parsedDict = parsedData as? [String:Any],
    let stop = parsedDict["Stop"] as? [String:Any],
    let name = stop["Name"] as? String,
    let latitude = stop["Latitude"] as? String,
    let longitude = stop["Longitude"] as? String else
    {
        print("Something Went Wrong")
        return
    }

    nameArray.append(name)
    latArray.append(latitude)
    longArray.append(longitude)

但是，以下代码确实有效：

if let parsedData = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String:Any]
{
    if let stop = parsedData?["Stop"] as? [String:Any]
    {
        if let latitude = stop["Latitude"] as? String, let longitude = stop["Longitude"] as? String, let name = stop["Name"] as? String
        {
            nameArray.append(name)
            latArray.append(latitude)
            longArray.append(longitude)
        }
    }
}

修改

在审核代码之后，问题似乎源于这一行：

guard let stop = parsedDict["Stop"] as? [String:Any] else
{
    print("Something went wrong")
    return
}

运行时，我在控制台中收到“出问题”，但运行时

if let stop = parsedData?["Stop"] as? [String:Any]
{
    print(stop)
}

我得到了有效的停止打印。

Answer 1

我自己在操场上运行你的守卫示例对我来说是成功的。我建议将你的警卫分成多个逻辑部分。例如，为了帮助您追踪错误，您可以将其更改为：

//Note: You should not force unwrap data here

guard let parsedData = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments) else{
    print("Serialization error"); return
}

guard
    let parsedDict = parsedData as? [String:Any],
    let stop = parsedDict["Stop"] as? [String:Any] else {

        print("Error casting to dictionary"); return
}

guard
    let name = stop["Name"] as? String,
    let latitude = stop["Latitude"] as? String,
    let longitude = stop["Longitude"] as? String else {

    print("Error casting dictionary values"); return
}

//Everything is ok here

Swift - Guard-let vs if-let

1 个答案: