ios - 如何快速检查 JSON 是否为空？

Question

我目前正在开发一个以下列格式带回 json 的应用程序

"location_subtype" = "somevalue"; "location_type" = Force; month = "2015-01"; "outcome_status" = { category = "somevalue"; date = "somevalue"; };

如果“outcome_status”有值，它会显示类别和日期，但是如果“outcome_value”没有任何值(在大多数情况下)，则显示如下

"location_subtype" = "somevalue"; "location_type" = Force; month = "2015-01"; "outcome_status" = ""; "persistent_id" = "";

问题是如何检查 outcome_status 的值是否不为“null”？

我尝试了以下方法将类别和日期存储到标签中，但它遇到了错误，第一个 if 语句应该检查值是否不为空，如果不为 null 则转到下一个 if 语句。但是它继续到下一个 if 语句，我得到以下错误

Thread 1: EXC_BAD_ACCESS(code=2, address=0x102089600)

if (dict["outcome_status"] != nil)
        {
            if ((dict["outcome_status"]as NSDictionary)["category"] != nil)
            {
                outcomeStatusLabel.text = ((dict["outcome_status"]as NSDictionary)["category"] as NSString)
                outcomeStatusLabel.font = UIFont.systemFontOfSize(14.0);
                outcomeStatusLabel.numberOfLines = 0
            }

            if ((dict["outcome_status"]as NSDictionary)["date"] != nil)
            {
                outcomeDateLabel.text = ((dict["outcome_status"]as NSDictionary)["date"] as NSString)
                outcomeDateLabel.font = UIFont.systemFontOfSize(14.0);
                outcomeDateLabel.numberOfLines = 0
            }
        }

如果我删除第一个 if 语句，它只会在“outcome_status”=“null”时崩溃，并且在“outcome_status”中有一些值时工作得很好

如果值为 = null，我需要做什么才能在第一个 if 语句处停止？

提前谢谢你。

Answer 1

尝试这样的事情:

快速代码:

if let outcome = dict["outcome_status"] as? NSDictionary {
    //Now you know that you received a dictionary(another json doc) and is not 'nil'
    //'outcome' is only valid inside this if statement

    if let category = outcome["category"] as? String {
        //Here you received string 'category'
        outcomeStatusLabel.text = category
        outcomeStatusLabel.font = UIFont.systemFontOfSize(14.0)
        outcomeStatusLabel.numberOfLines = 0
    }

    if let date = outcome["date"] as? String {
        //Here you received string 'date'
        outcomeDateLabel.text = date
        outcomeDateLabel.font = UIFont.systemFontOfSize(14.0)
        outcomeDateLabel.numberOfLines = 0
    }
}

这是使用 Json 的安全方式。