在将变量或常量声明设置为结尾为“()”的闭包中，每次访问变量时是否执行闭包？

Question

在Swift中的下面的代码中，每次调用变量‘整型’时还是在声明变量时执行闭包？

let integer: Int = {
    return 1
}()

有人知道那()叫什么吗？当我省略它时，会出现一个代码时错误，它告诉错误是什么，但它将()简单地称为'()'，而不告诉我这个错误是什么，也没有告诉我，当将'()‘放在上面的示例代码中时，它称为’()‘做什么。

函数生成预期的类型'Int'；您是想用'()‘来调用它吗？

以下代码是我在实际代码中使用()用于生产的地方，如果有人想知道的话：

var sharableZoneID = CKRecordZone.ID(zoneName: DatabaseNameStrings.recordZoneName, ownerName: CKCurrentUserDefaultName)

var userRecordID: CKRecord.ID? = {
    
    var localUserRecordID: CKRecord.ID? = nil
    
    containerCourier.fetchUserRecordID() {
        
        (recordID: CKRecord.ID?, error: Error?) in
        
        if let error = error {
            print(error.localizedDescription)
        }
        
        if let recordID = recordID {
            localUserRecordID = recordID
            sharableZoneID = CKRecordZone.ID(zoneName: DatabaseNameStrings.recordZoneName, ownerName: recordID.zoneID.ownerName)
        } else {
            print("couldn't get current user record id")
        }
        
    }

    return localUserRecordID
    
}()

Answer 1

首先，您需要使它成为一个计算属性，而不是一个闭包。

var sharableZoneID = CKRecordZone.ID(zoneName: DatabaseNameStrings.recordZoneName, ownerName: CKCurrentUserDefaultName)

var userRecordID:CKRecord.ID? = {
    
    var localUserRecordID: CKRecord.ID? = nil
    
    containerCourier.fetchUserRecordID() {
        
        (recordID: CKRecord.ID?, error: Error?) in
        
        if let error = error {
            print(error.localizedDescription)
        }
        
        if let recordID = recordID {
            localUserRecordID = recordID
            sharableZoneID = CKRecordZone.ID(zoneName: DatabaseNameStrings.recordZoneName, ownerName: recordID.zoneID.ownerName)
        } else {
            print("couldn't get current user record id")
        }
        
    }

    return localUserRecordID
    
}

第二，调用containerCourier.fetchUserRecordID() {是异步的，所以这个计算属性总是返回零，所以您需要这样做

func getId(completion:@escaping((CKRecord.ID?) ->()))  {
    
    var sharableZoneID = CKRecordZone.ID(zoneName: DatabaseNameStrings.recordZoneName, ownerName: CKCurrentUserDefaultName)
   
    containerCourier.fetchUserRecordID() {
        
        (recordID: CKRecord.ID?, error: Error?) in
        
        if let error = error {
            print(error.localizedDescription)
            completion(nil)
        }
        
        if let recordID = recordID { 
            sharableZoneID = CKRecordZone.ID(zoneName: DatabaseNameStrings.recordZoneName, ownerName: recordID.zoneID.ownerName)
            completion(recordID)
        } else {
            print("couldn't get current user record id")
            completion(nil)
        }
        
    }
    
}