ios - If else 语句定义一个 NSPredicate

Question

我正在尝试定义一个基于段 Controller 开关的谓词。

if self.streamtype == "case1" {
    let predicatearray = defaults.object(forKey: "case1") as! [String]
    let predicate = NSPredicate(format: "UserID IN %@" , predicatearray)
} else if self.streamtype == "case2" {
    let predicate = NSPredicate(format: "TRUEPREDICATE", argumentArray: nil)
} else {
    let predicatearray = defaults.object(forKey: "case3") as! [String]
    let predicate = NSPredicate(format: "UserID IN %@", predicatearray)
}

let publicData = CKContainer.default().publicCloudDatabase
let query = CKQuery(recordType: "Post", predicate: predicate)

我收到一条错误消息:

"Cannot be sent to an abstract object of class NSPredicate: Create a concrete instance!"

此外，它告诉我从未使用过谓词变量的初始化。我已经尝试用几种不同的方式编写函数，但这对我来说最有意义，因为我只需要在加载新信息时更新谓词，所以我只是将两个函数合二为一。

Answer 1

您在 if {} 或 else {} 范围内定义谓词，这就是它在范围外不可见的原因。

var predicate : NSPredicate!
if self.streamtype == "case1" {
    let predicatearray = defaults.object(forKey: "case1") as! [String]
    predicate = NSPredicate(format: "UserID IN %@", predicatearray)
} else if self.streamtype == "case2" {
    predicate = NSPredicate(format: "TRUEPREDICATE", argumentArray: nil)
} else {
    let predicatearray = defaults.object(forKey: "case3") as! [String]
    predicate = NSPredicate(format: "UserID IN %@", predicatearray)
}

let publicData = CKContainer.default().publicCloudDatabase
let query = CKQuery(recordType: "Post", predicate: predicate)