这是Objective-C的障碍吗？

Question

I came across some code in an opensource library called SIAlertView and I am not sure what it is doing? Specifically the two lines below? What is SIAleartViewHandler as it is not a class in the SIAlertView library?

typedef void(^SIAlertViewHandler)(SIAlertView *alertView);
@property (nonatomic, copy) SIAlertViewHandler willShowHandler;

SIAlertView.h

typedef void(^SIAlertViewHandler)(SIAlertView *alertView);
@property (nonatomic, copy) SIAlertViewHandler willShowHandler;
@property (nonatomic, copy) SIAlertViewHandler didShowHandler;
@property (nonatomic, copy) SIAlertViewHandler willDismissHandler;
@property (nonatomic, copy) SIAlertViewHandler didDismissHandler;

SIAlertView.m

[self transitionInCompletion:^{
    if (self.didShowHandler) {
        self.didShowHandler(self);
    }
    [[NSNotificationCenter defaultCenter] postNotificationName:SIAlertViewDidShowNotification object:self userInfo:nil];

    [SIAlertView setAnimating:NO];

    NSInteger index = [[SIAlertView sharedQueue] indexOfObject:self];
    if (index < [SIAlertView sharedQueue].count - 1) {
        [self dismissAnimated:YES cleanup:NO]; // dismiss to show next alert view
    }
}];

#pragma mark - SIAlertItem

@interface SIAlertItem : NSObject

@property (nonatomic, copy) NSString *title;
@property (nonatomic, assign) SIAlertViewButtonType type;
@property (nonatomic, copy) SIAlertViewHandler action;

@end

@implementation SIAlertItem

@end

Answer 1

The first line ( typedef void(^SIAlertViewHandler)(SIAlertView *alertView); ) defines a type of block, called SIAlertViewHandler .

The second line ( @property (nonatomic, copy) SIAlertViewHandler willShowHandler; ) defines a property which is going to store an instance of that block type.

Answer 2

Yes, that is a block.

The first line is creating a new type to add a bit of sanity to using said block (instead of having to repeat void(^)(SIAlertView *alertView) everywhere, you can just use SIAlertViewHandler .

SIAlertView.m is checking to see if the showHandler is set and, if so, calling the block.