来自 Objective-C 的 Swift 回调答案

【问题标题】：Swift callback from Objective-C来自 Objective-C 的 Swift 回调
【发布时间】：2018-12-13 15:57:39
【问题描述】：

在 Swift 应用程序中，我有一个 ViewController，它调用了一个新的 modal。这个modal 具有ViewController Objective-C 实现为ViewController_obj_c。

这个modal 是从Swift 代码中显示出来的，我想在Objective-C 代码完成后调用回调属性（带有UIImage 参数）。

我的回调属性 "signCompleteCallback" 不起作用。如何从Swift 填充回调属性并在Objective-C 中调用它？

SwiftViewController.swift：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "showModalSegue" {
        if let nextVC = segue.destination as? ViewController_obj_c {

            nextVC.signCompleteCallback = #selector(self.Test)
        }
    }
}

@objc func Test(image: UIImage)
{
    debugPrint("Test method was called as callback with image parameter")
}

ViewController_obj_c.h：

@interface ViewController_obj_c : UIViewController <UIPopoverPresentationControllerDelegate>


@property SEL signCompleteCallback;

- (IBAction)Done_Clicked:(id)sender;

ViewController_obj_c.m：

- (IBAction)Done_Clicked:(UIButton *)sender
{
    UIGraphicsBeginImageContext(_dV.bounds.size);
    [_dV.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

   [self signCompleteCallback]; // Here is the point when I want to call me callback and as a parameter i want to send image
}

【问题讨论】：

标签： objective-c swift callback delegates

【解决方案1】：

你为什么不使用 Objective-C block ？

SwiftViewController.swift：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "showModalSegue" {
        if let nextVC = segue.destination as? ViewController_obj_c {

            nextVC.signCompleteCallback = testMethod(image:) //`(image:)` is not needed when not ambiguous
        }
    }
}

func testMethod(image: UIImage) {
    debugPrint("Test method was called as callback with image parameter")
}

ViewController_obj_c.h：

@interface ViewController_obj_c : UIViewController<UIPopoverPresentationControllerDelegate>

typedef void (^signCompleteCallbackType)(UIImage * _Nonnull image); //Declare the block type

@property signCompleteCallbackType signCompleteCallback; //Declare the block property using the block type

- (IBAction)Done_Clicked:(id)sender;

@end

ViewController_obj_c.m：

- (IBAction)Done_Clicked:(UIButton *)sender
{
    UIGraphicsBeginImageContext(_dV.bounds.size);
    [_dV.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    self.signCompleteCallback(image);    //Use the block just like a normal function
}

【讨论】：

【解决方案2】：

我找到了一个解决方案，但我对他不满意。

如果有人提供更好的解决方案，我会很高兴。在这个解决方案中，我不喜欢创建一个必须在 Swift 部件中继承的新协议（创建一个新类或在现有的 SwiftViewcontroller 中继承它，没关系）

一种方法是在 Objective-C 中创建 @protocol：

@protocol ObjC_ManagerDelegate 
-(void) signCallBack: (UIImage *)image;
@end

ViewController_obj_c.h：

@interface ViewController_obj_c : UIViewController <UIPopoverPresentationControllerDelegate>

    @property (nonatomic, strong) id <ObjC_ManagerDelegate>delegate;

    - (IBAction)Done_Clicked:(id)sender;
@end

ViewController_obj_c.m：

- (IBAction)Done_Clicked:(UIButton *)sender
{
    UIGraphicsBeginImageContext(_dV.bounds.size);
    [_dV.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    [self.delegate signCallBack:image];
}

Swift 部分看起来像这样。创建一个新类并从ObjC_ManagerDelegate继承它：

class SwiftmanagerDelegate: ObjC_ManagerDelegate {
    func signCallBack(_ image: UIImage!) {
        // do something
    } 
}

最后以代表的身份填写新班级

SwiftViewController.swift：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "showModalSegue" {
        if let nextVC = segue.destination as? ViewController_obj_c {

            nextVC.delegate = SwiftmanagerDelegate()
        }
    }
}

【讨论】：