I am trying to generate sample data for an #IBDesignable control, so when building for IB I'm fooling the control into being its own datasource. The upshot is I'm adding some methods to a protocol only for use by IB, and as a good citizen I wish to remove these for a regular (non-IB build).
I've distilled my problem down to the following code fragment. My protocol looks like this:-
protocol TestProtocol {
#if TARGET_INTERFACE_BUILDER
func myControl(control:AnyObject, colorForIndex index:UInt) -> UIColor?
func myControl(control:AnyObject, textForIndex index:UInt) -> String?
#endif
}
This fails to compile, with a message that implies an method overloading error: "error: declaration conflicts with previous value". The error message is on the second function declaration, and refers to the first function as the previous declaration it's clashing with.
But these are not overloads, they have different signatures because of the named parameters. And this is such a standard delegate naming convention across Cocoa that I was resistant to renaming my methods without understanding why.
Removing the #if TARGET_INTERFACE_BUILDER fixes the problem, so it is no longer a pressing issue for me, but I am completely stumped as to why adding this conditional compilation would produce such a bizarre error?
I am not sure why it happens, but happen to find a reasonable workaround.
Just separate the two declarations as shown below:
protocol TestProtocol {
#if TARGET_INTERFACE_BUILDER
func myControl(control:AnyObject, colorForIndex index:UInt) -> UIColor?
#endif
#if TARGET_INTERFACE_BUILDER
func myControl(control:AnyObject, textForIndex index:UInt) -> String?
#endif
}
Related
I want to use flags to control the compiler in Swift. Like we use #ifdef, #ifndef, #else, #endif in C (and C++, Objective C, ....)
I found the way to do it on the net, but I hit a problem in the following case. Anyone reading will understand what I want.
Nevertheless the compiler complains. What is the way to go around? Of course without having to copy two times the same ten or more lines.
#if UseAds
class ViewController: UIViewController,XYZBannerDelegateProtocol {
#else
class ViewController: UIViewController {
#endif
Note that I got the information I am using here:
http://en.swifter.tips/condition-compile/
which is similar to what can be found here.
But none of these solves my problem. They only tell me the basic way to do it.
You can use like this :
class ViewController: UIViewController {
// Your common functions
}
#if UseAds
extension ViewController: XYZBannerDelegateProtocol {
// Your delegate methods
}
#endif
I am reading AWS SDK sample code on GitHub and saw these following two functions:
// MARK: NSObjectProtocol hack
override func isEqual(object: AnyObject?) -> Bool {
return super.isEqual(object)
}
override func `self`() -> Self {
return self
}
This is only one comment above "NSObjectProtocol hack", which doesn't really make sense to me. Could anyone explain what they are trying to do here?
This is a legacy code you can ignore when using the latest Swift. The earlier versions of Swift had issues recognizing that your mapper object indirectly inherits from NSObject and implements NSObjectProtocol. The current version of Swift does not have the issue, so you can safely ignore these two methods.
This is an example of using a keyword as an identifier. You have to place backtick marks before and after the keyword to use it as such. According to Apple's documentation (under the Identifiers section)
To use a reserved word as an identifier, put a backtick (`) before and after it. For example, class is not a valid identifier, but `class` is valid. The backticks are not considered part of the identifier; `x` and x have the same meaning.
The // MARK: NSObjectProtocol hack is used for commenting a section of code that allows Xcode to format the list of properties/methods etc. into groups.
I am starting to learn Swift, and have been following the very good Stanford University video lectures on YouTube. Here is a link if you are interested or it helps (although it isn't required to understand my problem):
Developing iOS 8 Apps with Swift - 2. More Xcode and Swift, MVC
While following the lectures I got to a point where (as far as I could tell) my code was identical to the code in the video but on my system I got a compiler error. After a lot of trial and error I have managed to reduce my code to two examples, one of which generates an error, the other or which doesn't, but I have no idea what is actually causing the error or how to resolve it.
The code which creates the error is:
import UIKit
class BugViewController: UIViewController
{
func perform(operation: (Double) -> Double) {
}
func perform(operation: (Double, Double) -> Double) {
}
}
This creates the following compiler error:
Method 'perform' with Objective-C selector 'perform: ' conflicts with previous declaration with the same Objective-C selector
By simply removing the sub-classing of UIViewController the code compiles:
import UIKit
class BugViewController
{
func perform(operation: (Double) -> Double) {
}
func perform(operation: (Double, Double) -> Double) {
}
}
Some other information which may or may not be relevant:
I have recently upgraded to Yosemite.
When I installed Xcode, I ended up with a Beta version (Version 6.3 (6D543q)) because (if I remember correctly) this was the version I needed to run on my version of OS X.
I am half hoping this is a bug in the compiler because otherwise this doesn't make any sense to me. Any help very gratefully received!
I myself am also taking the Standford course and I got stuck here for a long time too, but after some searching, I found something from here: Xcode release notes and it mentioned something below:
Swift 1.2 is strict about checking type-based overloading of #objc
methods and initializers, something not supported by Objective-C.
// Has the Objective-C selector "performOperation:".
func performOperation(op: NSOperation) { /* do something */ }
// Also has the selector "performOperation:".
func performOperation(fn: () -> Void) {
self.performOperation(NSBlockOperation(block: fn))
}
This code would work when invoked from Swift, but could easily crash
if invoked from Objective-C. To solve this problem, use a type that is
not supported by Objective-C to prevent the Swift compiler from
exposing the member to the Objective-C runtime:
If it makes sense, mark the member as private to disable inference of #objc.
Otherwise, use a dummy parameter with a default value, for
example: _ nonobjc: () = (). (19826275)
Overrides of methods exposed
to Objective-C in private subclasses are not inferred to be #objc,
causing the Swift compiler to crash. Explicitly add the #objc
attribute to any such overriding methods. (19935352)
Symbols from SDKs are not available when using Open Quickly in a
project or workspace that uses Swift. (20349540)
what i did was just adding "private" in front of the override method like this:
private func performOperation(operation: Double -> Double) {
if operandStack.count >= 1 {
displayValue = operation(operandStack.removeLast())
enter()
}
}
Objective-C does not support method overloading, you have to use a different method name. When you inherited UIViewController you inherited NSObject and made the class interopable to Obj-C. Swift on the other hand does support overloading, that's why it works when you remove the inheritance.
As it has already been answered, ObjC doesn't support method overloading (two methods with the same name) and In swift 2 under Xcode 7 there are two options to solve this kind of problems. One option is to rename the method using the attribute: #objc(newNameMethod:)
func methodOne(par1, par2) {...}
#objc(methodTwo:)
func methodOne(par1) {...}
another option to solve this problem in Xcode 7+ is by applying #nonobjc attribute to any method, subscript or initialiser
func methodOne() {...}
#nonobjc
func methodOne() {...}
The problem is UIViewController is an #objc class. When inheriting from UIViewController, BugViewController is also a #objc class.
This means it must conform to the rules of Objective-C selectors (the name of a method). The methods func perform(operation: (Double) -> Double) and func perform(operation: (Double, Double) -> Double) both have the same selector #selector(perform:). This is not allowed.
To resolve this, use different names: like func perform1(operation: (Double) -> Double) and func perform2(operation: (Double, Double) -> Double).
I think the best way to handle this is to give your perform() methods more descriptive names. What do these methods do? How do they change the state of the view controller? Look at the other UIViewController methods to get a feel for the style of method naming, or read Method Names Should Be Expressive and Unique Within a Class
From https://developer.apple.com/library/ios/releasenotes/DeveloperTools/RN-Xcode/Chapters/xc6_release_notes.html under "Xcode 6.3 Release Notes" -> "Swift Language Changes" you find
Swift now detects discrepancies between overloading and overriding in the Swift type system and the effective behavior seen via the Objective-C runtime.
I got the same error due to having having two methods with the same Obj-C signature:
static func prepareForUpSyncing(obj : NSManagedObject!) -> Bool
static func prepareForUpSyncing(objs : [NSManagedObject]!) -> Bool
I didn't want to mark one of them as #nonobjc due to possibility of unforseen consequences at runtime. (Someone can correct me if there is no possibility)
Resolved it by using Swift's external parameter name feature (I made external name same as local name) to the second method, which effectively changes the Obj-c method signature:
static func prepareForUpSyncing(objs objs : [NSManagedObject]!) -> Bool {
If I have a protocol, MyProtocol defined as:
protocol MyProtocol {
func myFunction() -> String
}
and I have a default implementation declared in an extension so that conformers can "optionally" implement the function:
extension MyProtocol {
func myFunction() -> String { return "" }
}
everything should work just dandy.
However, when a class conforms to that protocol and doesn't implement the functions, the compiler fails with Segmentation fault 11. Once the class implements the function, the error goes away and all is good with the world but it seems to defeat the purpose of defining default implementations in extensions.
Does anyone have any idea why this happens? Is it because the conforming class declares that it implements the methods so the compiler ignores what's written in the extension, can't find the methods and then crashes?
I also had a similar problem with protocol extensions and Segmentation fault 11.
In my case the problem was, that in the extension I put the mutating keyword before the function, but in the protocol there was no mutating. And instead on an error this lead to that Segmentation fault 11.
Maybe that helps a bit.
Working on a mixed framework. imported inside the Obj-C file but the internal classes are not visible, only the public ones.
The documentation clearly states the internal clasees should be available between Swift and Obj-C:
Importing Swift into Objective-C To import a set of Swift files in the same framework target as your Objective-C code, you don’t
need to import anything into the umbrella header for the framework.
Instead, import the Xcode-generated header file for your Swift code
into any Objective-C .m file you want to use your Swift code from.
Because the generated header for a framework target is part of the
framework’s public interface, only declarations marked with the public
modifier appear in the generated header for a framework target. You
can still use Swift methods and properties that are marked with the
internal modifier from within the Objective-C part of your framework,
as long they are declared within a class that inherits from an
Objective-C class. For more information on access-level modifiers, see
Access Control in The Swift Programming Language (Swift 2).
Code Sample (Create a new project with a framework)
// SwiftObject.swift
public class SwiftObject: NSObject {
public class func doSomething() {}
}
internal class YetAnotherSwiftObject: NSObject {
internal class func doSomething() {}
}
// SomeObject.m file
#implementation SomeObject
- (void)someMethod {
[SwiftObject doSomething];
}
- (void)someOtherMethod {
[YetAnotherSwiftObject doSomething]; // Use of undeclared identifier
}
#end
As indicated in the docs, declarations marked with internal modifier don't appear in the generated header, so the compiler does not know about them and thus complaints. Of course, you could send messages using performSelector approach, but that's not convenient and bug-prone. We just need to help the compiler know that those declarations are there.
First, we need to use #objc attribute variant that allows you to specify name for your symbol in Objective-C:
// SwiftObject.swift
#objc(SWIFTYetAnotherSwiftObject)
internal class YetAnotherSwiftObject: NSObject {
internal class func doSomething() {}
}
And then you just need to create #interface declaration with the methods you want to use in your code - so the compiler will be happy, and also apply SWIFT_CLASS macro with the symbol name you've specified earlier - so the linker would pick the actual implementation:
// SomeObject.m file
SWIFT_CLASS("SWIFTYetAnotherSwiftObject")
#interface YetAnotherSwiftObject : NSObject
+ (void)doSomething;
#end
#implementation SomeObject
- (void)someOtherMethod {
[YetAnotherSwiftObject doSomething]; // Should work now !!!
}
#end
I've used the interface declaration in .m file just for clarity, the better option would be to combine such declarations in .h file, and include it.
By declaring methods in that interface we're making a promise to compiler, and it won't complain if you'll put there a method that does not exist (or with wrong signature, etc.) Obviously, you'll crash in runtime in that case - so be cautious.
For me it just worked by checking: "Allow app extension API only". You find it by going to the project setting, select your target and then it is in the General tab under Deployment Info.
Can someone explain to me, why this does solve the problem?
While the above solution works (https://stackoverflow.com/a/33159964/5945317), it seems overly complicated and unintuitive:
Complicated, because it seems to add more things than necessary – I will provide a smoother solution below.
Unintuitive, because the objc macro SWIFT_CLASS resolves to SWIFT_RUNTIME_NAME, and the provided value is not actually the runtime name – nor is the objc class name in the header matching the Swift attribute param in #objc. Still, surprisingly, the solution works – but to me it is not clear why.
Here is what we have tested in our own project, and believe to be the better solution (using the example above):
// YetAnotherSwiftObject.swift
#objc(OBJCPREFIXYetAnotherSwiftObject)
internal class YetAnotherSwiftObject: NSObject {
#objc internal class func doSomething() {}
}
// OBJCPREFIXYetAnotherSwiftObject.h
#interface OBJCPREFIXYetAnotherSwiftObject : NSObject
+ (void)doSomething;
#end
That's it. The interface looks like a regular objc interface. This gives the added benefit that you can include it in other header files (which you cannot do if you use the SWIFT_CLASS macro, as it comes from the autogenerated Swift header file, which in turn you cannot include in an objc header, due to circular dependency).
On the Swift side, the only thing relevant is that you provide the class with the proper objc name. Mind that I only used the name prefix for language consistency – you can even just use YetAnotherSwiftObject everywhere (i.e., in the objc header and in the #objc attribute in Swift – but you need to keep this attribute with explicit naming in any case, and need to keep it consistent with the class name in the header).
This also makes your life easier if you're in the process of converting your objc framework step by step to Swift. You just keep the objc header as before, and now provide the implementation in Swift.
Methods and properties that are marked with the internal modifier and declared within a class that inherits from an Objective-C class are accessible to the Objective-C runtime.
so let's make use of that:
class MyInternalClass: NSObject {
#objc var internalProperty = 42
}
#interface MyPublicClass()
#end
#implementation MyPublicClass
+ (void) printValue {
Class myInternalClass = NSClassFromString(#"MyPackageNameIfAny.MyInternalClass");
id myInternalClassInstance = [myInternalClass new];
int value = [myInternalClassInstance performSelector:#selector(internalProperty)];
NSLog(#"Value is %d ", value); // "value is 42"
}
#end
Using the SWIFT_CLASS macro and #objc class attribute could easily lead to errors when archiving. This approach is safer.