UIActionsheet的block实现

IOS UIKIT framework的UIActionsheet是不支持block方式的，为什么我们需要block支持呢？

原因有

1. block的代码更灵活，而同一个NSObject派生对象里，通常只出现一个UIActionsheet delegate实现，出现多个情况变得复杂，需要if else判断，并且需要property 来保存 UIActionsheet以便在delegate回调中加以判断。

2.更麻烦的情况是，在有参数需要传递到delegate回调中时，更麻烦，代码将更乱。 

解决方法，便是引入block

client调用的例子

[sheet showInView:view          handler:^(UIActionSheet *actionSheet, NSInteger buttonIndex) {              if (buttonIndex == [actionSheet cancelButtonIndex]) {                  NSLog(@"Cancel button index tapped");              } else if (buttonIndex == [actionSheet destructiveButtonIndex]) {                  NSLog(@"Destructive button index tapped");              } else  {                  NSLog(@"Button %i tapped", buttonIndex);              }                                }];

源代码如下

#import "UIActionSheet+Blocks.h"
#import <objc/runtime.h>
/*
 * Runtime association key.
 */
static NSString *kHandlerAssociatedKey = @"kHandlerAssociatedKey";
@implementation UIActionSheet (Blocks)
#pragma mark - Showing
/*
 * Shows the sheet from a view.
 */
- (void)showInView:(UIView *)view handler:(UIActionSheetHandler)handler {
    
    objc_setAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey), handler, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self setDelegate:self];
    [self showInView:view];
}
/*
 * Shows the sheet from a bar button item.
 */
- (void)showFromBarButtonItem:(UIBarButtonItem *)item animated:(BOOL)animated handler:(UIActionSheetHandler)handler {
    
    objc_setAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey), handler, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self setDelegate:self];
    [self showFromBarButtonItem:item animated:animated];
}
/*
 * Shows the sheet from a rect.
 */
- (void)showFromRect:(CGRect)rect inView:(UIView *)view animated:(BOOL)animated handler:(UIActionSheetHandler)handler {
    
    objc_setAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey), handler, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self setDelegate:self];
    [self showFromRect:rect inView:view animated:animated];
}
/*
 * Shows the sheet from a tab bar.
 */
- (void)showFromTabBar:(UITabBar *)view handler:(UIActionSheetHandler)handler {
    
    objc_setAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey), handler, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self setDelegate:self];
    [self showFromTabBar:view];
}
/*
 * Shows the sheet from a toobar.
 */
- (void)showFromToolbar:(UIToolbar *)view handler:(UIActionSheetHandler)handler {
    
    objc_setAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey), handler, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self setDelegate:self];
    [self showFromToolbar:view];
}
#pragma mark - UIActionSheetDelegate
/*
 * Sent to the delegate when the user clicks a button on an action sheet.
 */
- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    
    UIActionSheetHandler completionHandler = objc_getAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey));
    
    if (completionHandler != nil) {
        
        completionHandler(actionSheet, buttonIndex);
    }
}
@end

实现分析

/*
 * Shows the sheet from a bar button item.
 */
- (void)showFromBarButtonItem:(UIBarButtonItem *)item animated:(BOOL)animated handler:(UIActionSheetHandler)handler {
    
    objc_setAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey), handler, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self setDelegate:self];
    [self showFromBarButtonItem:item animated:animated];
}

1.代码以category方式实现，更加方便的引入到我们的工程中，成本低，不引入新的class

2.通过objc_setAssociatedObject runtime函数，像class中加入handler property,以便在delegate里加调该block

#pragma mark - UIActionSheetDelegate
/*
 * Sent to the delegate when the user clicks a button on an action sheet.
 */
- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    
    UIActionSheetHandler completionHandler = objc_getAssociatedObject(self, (__bridge const void *)(kHandlerAssociatedKey));
    
    if (completionHandler != nil) {
        
        completionHandler(actionSheet, buttonIndex);
    }
}

3.在category中实现了delegate回调方法，并调用了该block handler.

https://github.com/emenegro/action-sheet-blocks