I have a protocol DataProviderDelegate which is defined below:
protocol DataProviderDelegate : class {
typealias Object
}
Now, I have a class which inherits this protocol as shown below:
extension ShoppingListTableViewController : DataProviderDelegate {
}
The error is that the ShoppingListTableViewController does not conform to the DataProviderDelegate protocol. I can see that I have not implemented the Object typealias but if it is required how do I do that?
You can try add this line in ShoppingListTableViewController hope this can help you :)
typealias Object = AnyObject
Related
I updated my project to Swift 2, and received a bunch of redundant conformance of XXX to protocol YYY. This happens especially often (or always) when a class conforms to CustomStringConvertible. Also some place with Equatable.
class GraphFeatureNumbersetRange: GraphFeature, CustomStringConvertible { // <--- get the error here
...
}
I suspect that I don't need to explicitly conform to a protocol when I implement var description: String { get }, or whatever methods the protocol requires. Should I just follow fixit instructions and remove all these? Does Swift now automatically infer the conformance if a class implements all the protocol's methods?
You'll get that error message in Xcode 7 (Swift 2) if a subclass declares conformance
to a protocol which is already inherited from a superclass. Example:
class MyClass : CustomStringConvertible {
var description: String { return "MyClass" }
}
class Subclass : MyClass, CustomStringConvertible {
override var description: String { return "Subclass" }
}
The error log shows:
main.swift:10:27: error: redundant conformance of 'Subclass' to protocol 'CustomStringConvertible'
class Subclass : MyClass, CustomStringConvertible {
^
main.swift:10:7: note: 'Subclass' inherits conformance to protocol 'CustomStringConvertible' from superclass here
class Subclass : MyClass, CustomStringConvertible {
^
Removing the protocol conformance from the subclass declaration
solves the problem:
class Subclass : MyClass {
override var description: String { return "Subclass" }
}
But the superclass must declare the conformance explicitly, it is
not automatically inferred from the existence of the description
property.
For googlers, I also got this error when including SwiftyJson in my Tests target and adding a swift test class, as it caused SwiftyJson to be compiled in again, and it declares NSNumber as Comparable. The solution was to only include it in the app target.
The point is that your GraphFeatureNumbersetRange is NSObject's subclass.
Which in its turn already conforms to CustomStringConvertible! That's it! Just delete this redundant protocol. Now you're declaring it twice! :-)
How can I cast a given object to a type and a protocol in order to call some methods that are defined as an extension
For Example:
extension Identifiable where Self: NSManagedObject, Self: JsonParseDescriptor {
func someMethod() { }
}
Now I have an object that I retrieved from Core data and I would like to cast it to the above protocols in order to call someMethod on it. I could cast to the protocols using protocol<Identifiable, JsonParseDescriptor> , but how can I include the NSManagedObejct type in it also?
Thanks
As of Swift 4, it is now possible to make mentioned cast directly without tricky workarounds. The task is accomplished similarly as we do protocol composition:
var myVar = otherVar as! (Type & Protocol)
No more need for extensions and bridge protocols.
What you're looking for it called a concrete same-type requirement. Unfortunately, it's not yet possible in Swift.
See ticket SR-1009 and SR-1447 for details. You should also checkout this answer.
In the mean-while, you can extend NSManagedObject with a dummy protocol with the methods you need:
protocol _NSManagedObject {
//the methods you want
}
extension NSManagedObject: _NSManagedObject {}
extension Identifiable where Self: _NSManagedObject, Self: JsonParseDescriptor {
func someMethod() { }
}
I'm writing a factory class that is trying to work with custom protocol defined functions. The compiler throws an error, because I don't know how to add a protocol definition to a function parameter.
Example:
protocol MyCustomFunctions {
func customFunction()
}
class MyVC: UIViewController, MyCustomFunctions {
func customFunction() {}
}
class Factory {
func createButton(specificVC: UIViewController) // need protocol here
{
specificVC.customFunction() // error thrown
}
}
How can one specific a protocol during a variable definition?
Or is there another way?
First of all ,convention says classes start with a Capital letter.
class MyVC: UIViewController, MyCustomFunctions {
func customFunction() {}
}
Then what you need is the correct type in the argument
class factory: NSObject {
func createButton(specificVC: MyVC) // you need a class that conforms to protocol here.
{
specificVC.customFunction() // no error anymore
}
}
You have another option. You can simply promise in the argument that you won't disclose the full type of the object ,you will only say it's an opaque object that conforms to protocol.
class factory: NSObject {
func createButton(specificVC: MyCustomFunctions) // you need a class that conforms to protocol here.
{
specificVC.customFunction() // no error anymore
}
}
BONUS:
The way you could have reasoned about this and find an answer is this>
Error is thrown when I call specificVC.customFunction()...Hmmm...so this object can only run this function if it is of type that actually HAS the function. So let's take a look at the argument type - UIViewController - ..UIViewController certainly doesn't have this function. It's the MyVC or the Protocol.
Type safety in Swift is very strict. Just "follow the type flow" and you will be good.
Let's assume I have five UIView objects which all conform to a particular protocol. I have an object which should maintain a list of these objects, and message them all when necessary.
protocol MyProtocol: AnyObject {
func doSomething()
}
The problem is, when I go to add these UIViews to a Set variable, the compiler produces an error because MyProtocol does not conform to Hashable. I can understand the reasoning for this, can anyone think of good ways to overcome this? In the meantime I considered using NSHashTable instead, but you lose the nice enumeration features of Sets.
Updating answer to post some sample code (this is still not working)
protocol MyProtocol: class, AnyObject {
func doSomething()
}
class MyClass {
var observers: Set<MyProtocol> = Set<MyProtocol>()
}
As you are defining protocol for class so you need to write 'class' keyword before inheriting any other protocol:
protocol MyProtocol: AnyObject, Hashable{
func doSomething()
}
class MyClass<T: MyProtocol> {
var observers: Set<T> = Set<T>()
}
Change your protocol to this and it will work fine.
You can refer Apple Documentation for further details.
I'm trying to pass a dictionary object to an Objective C protocol using swift.
the protocol code snippet is as follows:
#protocol MessageDelegate
- (void)handleNewMessageArrived:(NSDictionary *)messageContent;
#end
and this is the swift class the implements the protocol:
class ViewController: UIViewController, MessageDelegate
{
...
func handleNewMessageArrived(messageContent : NSDictionary!)
{
...
}
}
But the build fails, and the error I get is:
"the type 'ViewController' does not conform to protocol 'MessageDelegate"
I looked at this SO Question but it deals with a specific object type.
is there an error in the way I declare\implement the delegate method? or in the way I assume the arguments are mapped in swift?
I'm new to Swift so any Help will be much appreciated.
Try implementing the method in your Swift class like this:
func handleNewMessageArrived(messageContent: [NSObject : AnyObject]!) {
// Handle the message
}
In case of Swift 3, this is what you will need
func handleNewMessageArrived(messageContent: [AnyHashable : Any]!) {
// Handle the message
}