-
Notifications
You must be signed in to change notification settings - Fork 1
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
♻️ Extract delegate swizzling to single implementation
- Loading branch information
Showing
4 changed files
with
101 additions
and
182 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,82 @@ | ||
| // | ||
| // Swizzler.swift | ||
| // AppcuesKit | ||
| // | ||
| // Created by Matt on 2024-04-11. | ||
| // Copyright © 2024 Appcues. All rights reserved. | ||
| // | ||
|
|
||
| import Foundation | ||
|
|
||
| internal enum Swizzler { | ||
| /// Swizzling for delegate objects. | ||
| /// | ||
| /// This is unique because, | ||
| /// 1. We aren't certain of the class type that implements the delegate protocol at compile time. | ||
| /// This is the reason why this function takes an instance of the delegate instead of the delegate type. | ||
| /// 2. Delegate methods are frequently optional, so we can't rely on the implementation being there to swizzle. | ||
| /// If this is the case, we add an empty placeholder implementation and then swizzle that. | ||
| /// | ||
| /// - Parameters: | ||
| /// - targetInstance: Instance of the class to replace the method in. | ||
| /// - targetSelector: Selector of the method to replace. | ||
| /// - replacementOwner: Class containing the methods selected by `swizzleSelector` and `placeholderSelector`. | ||
| /// - placeholderSelector: Selector of the method to use the `targetSelector` method is not implemented. | ||
| /// This should be an empty function. | ||
| /// - swizzleSelector: Selector of the method to use as the replacement. | ||
| static func swizzle( | ||
| targetInstance: AnyObject, | ||
| targetSelector: Selector, | ||
| replacementOwner: AnyClass, | ||
| placeholderSelector: Selector, | ||
| swizzleSelector: Selector | ||
| ) { | ||
| // see if the currently assigned delegate has an implementation for the target selector already. | ||
| // these are optional methods in the protocol, and if they are not there already, we'll need to add | ||
| // a placeholder implementation so that we can consistently swap it with our override, which will attempt | ||
| // to call back into it, in case there was an implementation already - if we don't do this, we'll | ||
| // get invalid selector errors in these cases. | ||
| let targetClass: AnyClass = type(of: targetInstance) | ||
| let originalMethod = class_getInstanceMethod(targetClass, targetSelector) | ||
|
|
||
| if originalMethod == nil { | ||
| // this is the case where the existing delegate does not have an implementation for the target selector | ||
|
|
||
| guard let placeholderMethod = class_getInstanceMethod(replacementOwner, placeholderSelector) else { | ||
| // this should never be nil as it would be a developer error, but we must nil check this call | ||
| return | ||
| } | ||
|
|
||
| // add the placeholder, so it can be swizzled uniformly | ||
| class_addMethod( | ||
| targetClass, | ||
| targetSelector, | ||
| method_getImplementation(placeholderMethod), | ||
| method_getTypeEncoding(placeholderMethod) | ||
| ) | ||
| } | ||
|
|
||
| // swizzle the new implementation to inject our own custom logic | ||
|
|
||
| // this should never be nil as it would be a developer error, but we must nil check this call | ||
| guard let swizzleMethod = class_getInstanceMethod(replacementOwner, swizzleSelector) else { return } | ||
|
|
||
| // add the swizzled version - this will only succeed once for this instance, if its already there, we've already | ||
| // swizzled, and we can exit early in the next guard | ||
| let addMethodResult = class_addMethod( | ||
| targetClass, | ||
| swizzleSelector, | ||
| method_getImplementation(swizzleMethod), | ||
| method_getTypeEncoding(swizzleMethod) | ||
| ) | ||
|
|
||
| guard addMethodResult, | ||
| let originalMethod = originalMethod ?? class_getInstanceMethod(targetClass, targetSelector), | ||
| let swizzledMethod = class_getInstanceMethod(targetClass, swizzleSelector) else { | ||
| return | ||
| } | ||
|
|
||
| // finally, here is where we swizzle in our custom implementation | ||
| method_exchangeImplementations(originalMethod, swizzledMethod) | ||
| } | ||
| } |