目标C前向声明的协议方法类型在Swift上不可用

Question

我有以下Objective C类标题：

@protocol CustomKeyboard;
@class CustomKeyboardView;
@protocol CustomKeyboardViewProtocol <NSObject>

- (void)customKeyboardView:(UIView<CustomKeyboard> *)customKeyboard  numberPress:(UIButton *)sender;

@end

@protocol CustomKeyboard <NSObject>

@required

-(id)initWithDelegate:(id<CustomKeyboardViewProtocol>)delegate;
-(void)reload;

@property (nonatomic, weak) UITextField * textField;
@property (nonatomic, weak) id<CustomKeyboardViewProtocol> delegate;

@end

@interface CustomKeyboardView : UIView <CustomKeyboard>
{
    IBOutlet UIView *keyboardView;
}

- (void)hide;
- (void)show;

@end

Swift中的这个类正在尝试采用该协议，但我收到的方法中的类型错误，并且自动完成已经消失：

extension MyViewController: CustomKeyboardViewProtocol {

    func customKeyboardView(_ customKeyboard: UIView!, numberPress sender: UIButton!) {
    }

}

错误说：

Candidate has non-matching type '(UIView!, UIButton!) -> ()'

任何线索，如果错误是因为协议中的循环依赖还是关于类型？我刚刚更新到Xcode 9和Swift 4，并更新到推荐的设置，它曾经工作得很好。