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定义：
returnType (^funcName)(paramType paraName) = ^(paramType paraName){};
作为方法参数时：
- (void)fun:( returnType (^funcName)(paramType paraName) ) blockName{}
typedef:
typedef returnType (^funcName)(paramType paraName);
防止block发生循环引用：
__weak __typeof(self) weakSelf = self;
AController *vc = [[AController alloc] initWithCallback:^{ [weakSelf.button setTitleColor:[UIColor greenColor] forState:UIControlStateNormal]; }];
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原文地址：http://www.cnblogs.com/ficow/p/5222831.html
