《Effective Objective-C 2.0》读书笔记（二）——对象

6.理解“属性”这一概念

原子性

• nonatomic:效率高
  atomic:默认

读写

• readwrite:默认
• readonly

内存管理

• assign：默认
  1.简单赋值
  2.基础数据类型（NSInteger、CGFloat）和C数据类型（int，float，double，char）
  3.不更改引用计数

• retain：引用计数加1

• copy：建立引用计数=1的对象，释放旧对象

• strong：拥有关系
  设置新值时，先保留新值，释放旧值，再设置新值，类似retain

• weak：非拥有关系
  1.设置新值时，不保留新值，不释放旧值，类似assign
  2.对象释放时，属性值会变成nil

• unsafe_unretained：非拥有关系
  1.类似assign，适用对象类型
  2.目标对象释放后，属性值不会自动清空，不安全

7.在对象内部尽量直接访问实例变量

• 速度快
• 不会调用“设置方法”
• 不会触发KVO
• 不方便查错

 -(void)example7{
 
 
pr_obj(@"start");

for(int i=0 ;i<1000000;i++){

    [self example7_set];

    [self example7_get];

}

pr_obj(@"end");


pr_obj(@"dotMethod_start");

for(int i=0 ;i<1000000;i++){

    [self example7_set_dotMethod];
    [self example7_get_dotMethod];


}

pr_obj(@"dotMethod_end");
 
 
}
 
 
-(void)example7_set_dotMethod{
 
 
self.dotMethod_arr = @[@"aaaa"];
 
 
}
 
 
-(NSArray *)example7_get_dotMethod{
 
 
return self.dotMethod_arr;
 
 
}
 
 
-(void)example7_set{
 
 
_arr = @[@"aaaa"];
 
 
}
 
 
-(NSArray *)example7_get{
 
 
return _arr;
 
 
}
 
 

结果：

example7

直接访问方式：691-410 = 281ms
点方法访问方式：1017-691 = 326ms

折中方案：写入实例变量时，通过“设置方法”；读取实例变量时，直接访问

• 提高读取速度

• 控制对属性的写入操作

8.理解“对象等同性”这一概念

==:比较指针本身

isEqual:比较两个对象

isEqualToString:速度更快

相同的对象有相同的hash码，但hash码相同对象未必相同

 -(void)example8_equal{
 
 
NSString *str1 = @"str1:123";

NSString *str2 = [NSString stringWithFormat:@"str1:%i",123];

BOOL equalA = (str1 == str2);

BOOL equalB = [str1 isEqualToString:str2];

BOOL equalC = [str1 isEqual:str2];

pr_int(equalA);

pr_int(equalB);

pr_int(equalC);

pr_int([str1 hash]);

pr_int([str2 hash]);
 
 
}
 
 

结果：

example8_equal

 
 
-(void)example8_set{
 
 
NSMutableSet *set = [NSMutableSet new];



NSMutableArray *arrayA = [@[@1,@2] mutableCopy];

[set addObject:arrayA];

pr_obj(set);



NSMutableArray *arrayB = [@[@1,@2] mutableCopy];

[set addObject:arrayB];

pr_obj(set);



NSMutableArray *arrayC = [@[@1] mutableCopy];

[set addObject:arrayC];

pr_obj(set);



[arrayC addObject:@2];

pr_obj(set);



NSSet *setB = [set copy];

pr_obj(setB);
 
 
}
 
 

结果：

example8_set

9.以“类族模式”隐藏实现细节

把实现细节隐藏在简单的公共接口后面

Employee：

 
 
import 
 
 
typedef NS_ENUM(NSInteger,EmployeeType) {
 
 
EmployeeTypeDeveloper,

EmployeeTypeProducter,

EmployeeTypeTester
 
 
};
 
 
@interface Employee : NSObject
 
 
+(Employee *)employeeWithType:(EmployeeType)type;
 
 
-(void)doWork;
 
 
@end
 
 
import "Employee.h"
 
 
import "EmployeeTester.h"
 
 
import "EmployeeDeveloper.h"
 
 
import "EmployeeProducter.h"
 
 
@implementation Employee
 
 
+(Employee *)employeeWithType:(EmployeeType)type{
 switch (type) {
 
 
    case EmployeeTypeTester:

        return [EmployeeTester new];

        break;

    case EmployeeTypeDeveloper:

        return [EmployeeDeveloper new];

        break;

    case EmployeeTypeProducter:

        return [EmployeeProducter new];

        break;

}
 
 
}
 
 
-(void)doWork{
 
 
}
 
 
@end
 

EmployeeDeveloper：

 
 
import "Employee.h"
 
 
@interface EmployeeDeveloper : Employee
 
 
@end
 
 
import "EmployeeDeveloper.h"
 
 
@implementation EmployeeDeveloper
 
 
-(void)doWork{
 
 
pr_obj(@"do developer's work");
 
 
}
 
 
@end
 
 

实现：

 -(void)example9{
 
 
Employee *developer = [Employee employeeWithType:EmployeeTypeDeveloper];

[developer doWork];

BOOL isMember = [developer isMemberOfClass:[Employee class]];

pr_int(isMember);

BOOL isKind = [developer isKindOfClass:[Employee class]];

pr_int(isKind);
 
 
}
 

结果：

example9

10.在既有类中使用关联对象存放自定义数据

• 可以通过“关联对象”机制来把两个对象连接起来

• 但不建议使用，也许会产生循环引用

• objc_getAssociatedObject

• objc_setAssociatedObject

正常方式：

 -(void)alertView{
 
 
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"" 
 
 
message:@"message" delegate:self cancelButtonTitle:@"cancle" otherButtonTitles:@"ok",
 nil];
 
 
[alertView show];
 
 
}
 
 
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:
 (NSInteger)buttonIndex{
 
 
if(buttonIndex ==0){

    pr_obj(@"cancle");

}else if (buttonIndex ==1){

    pr_obj(@"ok");

}
 
 
}
 

关联对象方式：

 -(void)alertViewWithBlock{
 
 
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"" 
 
 
message:@"message" delegate:self cancelButtonTitle:@"cancle" otherButtonTitles:@"ok",
 
 
nil];
 
 
void (^block)(NSInteger) = ^(NSInteger buttonIndex){

    if(buttonIndex ==0){

        pr_obj(@"cancle");

    }else if (buttonIndex ==1){

        pr_obj(@"ok");

    }

};


objc_setAssociatedObject(alertView, @"alertViewKey", block, 
 
 
OBJC_ASSOCIATION_COPY);
 
 
[alertView show];
 
 
}
 
 
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex{
 
 
void (^block)(NSInteger) = objc_getAssociatedObject(alertView, @"alertViewKey");

block(buttonIndex);
 
 
}