I'm converting some code from Objective C to Swift so I can get a handle on Swift.
Basically, in Objective C, I had a header file containing some global constants which were accessible in other Objective C classes.
I changed my .h file to be .swift and changed the constants to look like:
public let INVALID_INTEGER_VALUE = (-32768)
public let INVALID_LONGLONG_VALUE = (0x8000000000000000)
...
But when I try to access these in another Swift file, the compiler gives "Use of unresolved identifier..." I tried importing my .swift file, but that also didn't work (as far as I can tell, I shouldn't need to import any of my swift files as they are part of the same module).
Any thoughts?
You could also run into this if the file that is trying to use the constant has been added to another target (like the tests target) that the file containing the constants has not been added to.
Related
I see all kinds of examples for using a file or an extension but I am trying to call let imag = NSWorkspace.shared.icon(for: <#T##UTType#>) and I don't see any init method in UUType that takes a identifier e.g. folder.
UTType is declared in the Uniform Type Identifiers framework.
All uou need to do is import UniformTypeIdentifiers and then you'll be able to write things like UTType.folder.
I'm still a newbie to swift and I can't get a clear answer on a couple things.
So far I've just been using a single file in playgrounds.
If I want to use more files, how can I access data (variables and functions) from classes created there in my main file that controls the view?
From what I understand having multiple files would just be for convenience so I don't have could to write it again.
(Also on the side) what does it mean when a function has private, public or just 'func'?
I'm using swift 3 playgrounds
Thanks
Making things public will make them importable from other modules. Making it private will make it only accessible by methods within its containing scope (encapsulation). For code that lives at the top level, this scope is the entire .swift file it lives in. Without either access modifier (just bare “func”), your thing will default to internal, which means it is accessible from any other code within the same module, but not by code in a different module.
A special case is the fileprivate modifier which restricts access to the .swift file the code lives in. For code that does not live in a class or struct, this does the exact same thing as private. Some Swift designers discourage use of this modifier, and it may be removed in future versions of Swift.
There is a fifth access modifier in Swift, open, which does the exact same thing as public, except it also allows subclassing, and only applies to classes. This one is rarely used, but useful for certain library interfaces.
To import all the public symbols in a module, use
import Module
To import a single public symbol, use
import var Module.variable
import func Module.function
import struct Module.structure
import class Module.class
...
Im using Xcode 7.2 and I wanted to pass a variable between .swift files. I tried using static variables inside structs as such: in file 1 and then use this variable as such in file 2. But Xcode doesn't recognize the struct. What am I doing wrong? Thanks!
You need to specify that SomeStruct is defined in File1.
So the new variable in File2 would be declared as:
var someOtherVar = File1.SomeStruct().someVariable
I want to declare an Objective-C method with a custom Swift class as one of it's arguments, like this:
+ (void)doCalculationsWithACustomSwiftObject:(CustomSwiftClass *)swiftObject andADictionanary:(NSDictionary *)ordinaryDictionary;
The aim is to call this method from Swift, pass an instance of the custom class "CustomSwiftClass.swift" so that the Objective-C code can access its properties. Is it possible, and if so, how do I declare the "CustomSwiftClass" to make the compiler accept it?
A couple of thoughts:
To make Swift class accessible to your Objective-C code, you have to import the system generated header. As the documentation says:
When you import Swift code into Objective-C, you rely on an Xcode-generated header file to expose those files to Objective-C. This automatically generated file is an Objective-C header that declares the Swift interfaces in your target. It can be thought of as an umbrella header for your Swift code. The name of this header is your product module name followed by adding "-Swift.h". (You’ll learn more about the product module name later, in Naming Your Product Module.)
For example, your Objective-C file would import this generated header:
#import "MyApp-Swift.h"
For more information, see Importing Swift into Objective-C section of the Using Swift with Cocoa and Objective-C: Mix and Match
If you're not seeing the xxx-Swift.h file, double check your target settings:
(Note, I searched for "swift" in the settings to narrow down the results.)
As you'll see, the following are all set:
"Install Objective-C Compatibility Header" is set to "Yes";
The "Objective-C Generated Interface Header Name" is set (and matches what I imported into my Objective-C code);
The "Objective-C Bridging Header" is also specified.
Note, the Objective-C bridging header is ostensibly solely for the purpose of making the Objective-C classes available to the Swift code (and you're currently trying to accomplish the converse), but I notice that this affects what code is generated in the compatibility header, too. So make sure you have a bridging header, too.
Of course, make sure your Swift file is included in the list of compile sources:
And make sure the class is subclassed from NSObject:
import UIKit
class MyObject: NSObject {
var text: String?
var value: Int = 0
}
Note, some Swift types are not available to Objective-C code. For example, Objective-C cannot not use some optional types (e.g. an optional type such as Int? will not work, whereas an optional class type of String? will). So if you are seeing the class, but not some of the properties, make sure they're Objective-C compatible.
But I gather from your question that you're having more fundamental problems, that you're not finding the -Swift.h header at all. But once you solve that, this is a consideration for individual properties.
In my app delegate class I define a constant like so:
#define kSomeConstant #"My_Constant_Value"
I then want to make use of this constant in another viewController so I defined it again exactly as above. I now get the message:
'kSomeConstant' macro redefined
Why is this the case? Is there some other way I can access the constant?
Simply redefining the constant (ie : same constant name). Choose another name, or define it just one time in a header file to access the constant value every where you import that header.
It's likely been defined twice among the sources which are visible to the compiler. the compiler may tell you where the previous definition is if you look into the message in more detail.
To avoid this problem entirely, declare your NSString constants like this:
file.h - declaration:
extern NSString* const kSomeConstant;
file.m/mm - definition:
NSString* const kSomeConstant = #"My_Constant_Value";
Then when you need to use the constant, just #include "file.h".
The compiler has encountered two definitions of the macro. Probably you defined it in a header file and then defined it again in a .m file.
If you can't figure out where the two definitions come from, try preprocessing the file with the error (in Xcode 4.2 this is under generate output in the product menu). You can then do a search for kSomeConstant and that should tell you where it comes from.