BlocksKit 是一个开源的框架,对 Cocoa 进行了扩展,将许多需要通过 delegate 调用的方法转换成了 block。在很多情况下,blocks 比 delegate 要方便简单,因为 block 是紧凑的,可以使代码简洁,提高代码可读性,另外 block 还可以进行异步处理。使用 block 要注意避免循环引用。
BlocksKit 的所有方法都以 bk_
开头,这样可以方便地列出所有 BlocksKit 的所有方法。BlocksKit 主要目录结构
最常用的是 UIKit Category,它为 UIAlertView,UIActionSheet,UIButton,UITapGestureRecognizer 等提供了 blocks。
UIAlertView 和 UIActionSheet 用法示例:
UIAlertView *alertView = [[UIAlertView alloc] bk_initWithTitle:@"提示" message:@"提示信息"]; [alertView bk_setCancelButtonWithTitle:@"取消" handler:nil]; [alertView bk_addButtonWithTitle:@"确定" handler:nil]; [alertView bk_setDidDismissBlock:^(UIAlertView *alert, NSInteger index) { if (index == 1) { NSLog(@"%ld clicked",index); } }]; [alertView show];
[[UIActionSheet bk_actionSheetCustomWithTitle:nil buttonTitles:@[@"查看", @"退出"] destructiveTitle:nil cancelTitle:@"取消" andDidDismissBlock:^(UIActionSheet *sheet, NSInteger index) { }] showInView:self.view];
UIButton 和 UITapGestureRecognizer 用法示例:
UIButton *button = [[UIButton alloc] init]; [button bk_addEventHandler:^(id sender) { } forControlEvents:UIControlEventTouchUpInside];
UITapGestureRecognizer *tapGestureRecognizer = [UITapGestureRecognizer bk_recognizerWithHandler:^(UIGestureRecognizer *sender, UIGestureRecognizerState state, CGPoint location) { if (state == UIGestureRecognizerStateRecognized) { ... } }];
UIButton 和 UIGesture 将 target-action 转换成 block,实现较简单:
- (id)bk_initWithHandler:(void (^)(UIGestureRecognizer *sender, UIGestureRecognizerState state, CGPoint location))block delay:(NSTimeInterval)delay { self = [self initWithTarget:self action:@selector(bk_handleAction:)]; if (!self) return nil; self.bk_handler = block; self.bk_handlerDelay = delay; return self; } - (void)bk_handleAction:(UIGestureRecognizer *)recognizer { void (^handler)(UIGestureRecognizer *sender, UIGestureRecognizerState state, CGPoint location) = recognizer.bk_handler; if (!handler) return; ... if (!delay) { block(); return; } ... }
delegate 转换成 block 实际上使用了消息转发机制,是 BlocksKit 源码中最难理解的部分。
当一个对象收到它没实现的消息的时候,通常会发生如下的情况。
+(BOOL)resolveInstanceMethod:(SEL)aSEL
,如果对象在这里动态添加了selector 的实现方法,则消息转发结束,否则执行步骤2 - (id)forwardingTargetForSelector:(SEL)aSelector
,在这里你可以将消息转发给其他对象,如果实现则消息转发结束,否则执行步骤3 -(void)forwardInvocation:(NSInvocation *)invocation
在这一步,你可以修改消息的任何内容,包括目标(target),selector,参数。如果没有实现在这里还未实现转发则程序将抛出异常。 BlocksKit 动态代理实现方式是最后一步,即 -(void)forwardInvocation:(NSInvocation *)invocation
,使得动态代理能够接受任意消息。
以UIAlertView为例,UIAlertView在运行时动态关联了A2DynamicUIAlertViewDelegate
@implementation UIAlertView (BlocksKit) @dynamic bk_willShowBlock, bk_didShowBlock, bk_willDismissBlock, bk_didDismissBlock, bk_shouldEnableFirstOtherButtonBlock; + (void)load { @autoreleasepool { [self bk_registerDynamicDelegate]; [self bk_linkDelegateMethods:@{ @"bk_willShowBlock": @"willPresentAlertView:", @"bk_didShowBlock": @"didPresentAlertView:", @"bk_willDismissBlock": @"alertView:willDismissWithButtonIndex:", @"bk_didDismissBlock": @"alertView:didDismissWithButtonIndex:", @"bk_shouldEnableFirstOtherButtonBlock": @"alertViewShouldEnableFirstOtherButton:" }]; } }
A2DynamicUIAlertViewDelegate 是 A2DynamicDelegate 的子类,并实现了UIAlertViewDelegate 的方法
代理消息的转发由 A2DynamicDelegate 完成
- (void)forwardInvocation:(NSInvocation *)outerInv { SEL selector = outerInv.selector; A2BlockInvocation *innerInv = nil; if ((innerInv = [self.invocationsBySelectors bk_objectForSelector:selector])) { [innerInv invokeWithInvocation:outerInv]; } else if ([self.realDelegate respondsToSelector:selector]) { [outerInv invokeWithTarget:self.realDelegate]; } }
注: 文章由我们 iOS122( http://www.ios122.com)的小伙伴 @鱼
整理,喜欢就一起参与: iOS122 任务池