xcode 如何在 swift 'AnyObject' 中从 coredata 字典中打印出值没有名为 'username 的成员？
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How to print out value from coredata dictionary in swift 'AnyObject' does not have a member named 'username?
提问by Rolando
I am trying to print out the value "username" from my coredata entity.
我试图从我的核心数据实体中打印出值“用户名”。
var request = NSFetchRequest(entityName: "Users")
request.returnsObjectsAsFaults = false
var results = context.executeFetchRequest(request, error: nil)
if (results?.count > 0) {
for result: AnyObject in results! {
println(result.username)
}
}
The line println(result.username) is giving me a compile error of 'AnyObject' does not have a member named 'username'.
行 println(result.username) 给了我一个编译错误“AnyObject”没有名为“username”的成员。
回答by Martin R
You have to cast the array of managed object to the correct type:
您必须将托管对象数组强制转换为正确的类型：
for result in results! as [Users] {
println(result.username)
}
This assumes that you have created a managed object subclass for the "Users" entity.
这假设您已经为“用户”实体创建了一个托管对象子类。
You should also distinguish whether executeFetchRequest()returned nil(i.e. the fetch request failed), or 0(i.e. no objects found),
and use the errorparameter:
您还应该区分是executeFetchRequest()返回nil（即获取请求失败）还是0（即未找到对象），并使用error参数：
var error : NSError?
if let results = context.executeFetchRequest(request, error: &error) {
if (results.count > 0) {
for result in results as [Users] {
println(result.username)
}
} else {
println("No Users")
}
} else {
println("Fetch failed: \(error)")
// Handle error ...
}
Update for Swift 2/Xcode 7with try/catch error handling:
使用 try/catch 错误处理更新Swift 2/Xcode 7：
do {
let results = try context.executeFetchRequest(request) as! [Users]
if (results.count > 0) {
for result in results {
print(result.username)
}
} else {
print("No Users")
}
} catch let error as NSError {
// failure
print("Fetch failed: \(error.localizedDescription)")
}
Note that the forced cast as! [Users]is acceptable here.
The returned objects are always instances of the corresponding class as configured in the Core Data model inspector, otherwise you have
a programming errorwhich should be detected early.
请注意，as! [Users]这里可以接受强制转换。返回的对象始终是 Core Data 模型检查器中配置的相应类的实例，否则您应该及早检测到编程错误。
回答by sean woodward
Martin's answerdefinitely lets you access the properties of your object, but the cast is forced. Like it or not, Swift's strong type system is the future. When returning results from a fetch request, you might consider testing for the type.
Martin 的回答绝对可以让您访问对象的属性，但强制转换。不管喜欢与否，Swift 的强类型系统是未来。从获取请求返回结果时，您可能会考虑测试类型。
func executeFetchRequestT<T:AnyObject>(request:NSFetchRequest, managedObjectContext:NSManagedObjectContext, error: NSErrorPointer = nil) -> [T]? {
var localError: NSError? = nil
if let results:[AnyObject] = managedObjectContext.executeFetchRequest(request, error: &localError) {
if results.count > 0 {
if results[0] is T {
let casted:[T] = results as [T]
return .Some(casted)
}
if error != nil {
error.memory = NSError(domain: "error_domain", code: 0, userInfo: [NSLocalizedDescriptionKey: "Object in fetched results is not the expected type."])
}
} else if 0 == results.count {
return [T]() // just return an empty array
}
}
if error != nil && localError != nil {
error.memory = localError!
}
return .None
}
Using this approach you can type your results and get an error if the type is incorrect.
使用这种方法，您可以输入结果，如果类型不正确，则会出现错误。
var fetchError:NSError? = nil
if let results:[Users] = executeFetchRequestT(fetchRequest, managedObjectContext: managedObjectContext, error: &fetchError) {
for user in results {
// access the results with confidence of the correct type
}
} else {
// should have an error condition, handle it appropriately
assertFailure("something bad happened")
}
回答by brokenrhino
Change your for loop to this
将您的 for 循环更改为此
for result: AnyObject in results! {
if let user: AnyObject = result.valueForKey("username") {
println(user)
}
}
The fix is using valueForKey("String")
修复是使用 valueForKey("String")
