ios – 不使用桥接头访问私有UIKit功能

考虑私有C函数 _UICreateScreenUIImage,它返回当前设备屏幕的UIImage快照：

OBJC_EXTERN UIImage *_UICreateScreenUIImage(void) NS_RETURNS_RETAINED;

我可以把它放在一个桥接头,并在Swift中访问它：

MyApp的桥接,Header.h

@import UIKit;
UIImage *_UICreateScreenUIImage(void) NS_RETURNS_RETAINED;

MyClass.swift

let image = _UICreateScreenUIImage()
print(image) // <UIImage: 0x7fc4ba6081c0>,{375,667}

有没有办法我可以访问_UICreateScreenUIImage在纯Swift不使用桥接头？

最初的想法是在UIImage上创建一个扩展,但扩展是期望我在扩展中声明该函数的主体：

extension UIImage {
    public func _UICreateScreenUIImage(_: Void) -> UIImage // "Expected '{' in body of function declaration"
}

这个实现有缺陷,因为_UICreateScreenUIImage不是UIImage上的一种方法.

在纯粹的Swift中暴露和访问这种方法？

人们似乎把我的问题与“我如何拍摄截图”混淆？这不是我在问的.我问我如何访问UIImage * _UICreateScreenUIImage(void);在斯威夫特.它可以是任何私有方法,例如(UIImage *)_ deviceSpecificImageNamed：(NSString *)name inBundle：(NSBundle *)bundle;或(UIImage *)_ pu_PhotosUIImage命名：(NSString *)名称;
.

解决方法

这比你想象的要容易得多：

@asmname("_UICreateScreenUIImage")
func _UICreateScreenUIImage() -> UIImage

// That's it – go ahead and call it:
_UICreateScreenUIImage()

事实上,@asmname实际上已经在2.3版本中更改为@_silgen_name,因此可以随时进行相应的调整：

@_silgen_name("_UICreateScreenUIImage")
func _UICreateScreenUIImage() -> UIImage

据我所知,@_silgen_name不提供Objective-C方法的解决方案.为此,还有更强大的Objective-C运行时API：

let invokeImageNamed: (String,NSTimeInterval) -> UIImage? = {
    // The Objective-C selector for the method.
    let selector: Selector = "animatedImageNamed:duration:"
    guard case let method = class_getClassMethod(UIImage.self,selector)
        where method != nil else { fatalError("Failed to look up \(selector)") }

    // Recreation of the method's implementation function.
    typealias Prototype = @convention(c) (AnyClass,Selector,NSString,NSTimeInterval) -> UIImage?
    let opaqueIMP = method_getImplementation(method)
    let function = unsafeBitCast(opaqueIMP,Prototype.self)

    // Capture the implemenation data in a closure that can be invoked at any time.
    return { name,interval in function(UIImage.self,selector,name,interval) }
}()

extension UIImage {
    // Convenience method for calling the closure from the class.
    class func imageNamed(name: String,interval: NSTimeInterval) -> UIImage? {
        return invokeImageNamed(name,interval)
    }
}

UIImage.imageNamed("test",interval: 0)

至于处理NS_RETURNS_RETAINED,则不会为您生成.相反,您可以使用返回类型的非托管,并将其包装在函数中,以方便您：

@_silgen_name("_UICreateScreenUIImage")
func _UICreateScreenUIImage() -> Unmanaged<UIImage>
func UICreateScreenUIImage() -> UIImage {
    return _UICreateScreenUIImage().takeRetainedValue()
}