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Contents
  1. 1. 苹果KVC文档
    1. 1.1. 一切都建立在key-value coding 键值对
    2. 1.2. key 和 keyPath
    3. 1.3. Getting Attribute Values Using Key-Value Coding
    4. 1.4. Setting Attribute Values Using Key-Value Coding
    5. 1.5. Key-Value Coding Accessor Methods
    6. 1.6. NSArray、NSSet Ivar Getter Indexed Accessors
    7. 1.7. NSMutableArray、NSMutableSet Ivar Mutable Indexed Accessors
    8. 1.8. @property声明的属性做了一些什么
    9. 1.9. kvc设置对象的实例变量 与 调用对象属性方法 的区别
    10. 1.10. KVC实际上是根据key查找Class中对应的Ivar，继而对找到的Ivar进行值的存取
    11. 1.11. 使用KVC修改私有成员变量Ivar的值
    12. 1.12. 还可以直接使用runtime函数，直接获取key对应的Ivar，进而进行实例变量值的存取
    13. 1.13. 所以我觉得setValue:forKey:的底层实现可能是利用runtime完成:
    14. 1.14. key找不到时，处理异常
    15. 1.15. KVC键值对赋值提供两种方式
    16. 1.16. 使用valueForKeyPath:直接读取一个对象的数组内每一个对象的变量值，并进行基本运算
    17. 1.17. dictionaryWithValuesForKeys:/setValuesForKeysWithDictionary: ，对象与字典之间的快速转换
    18. 1.18. 使用KVC替换TabBarController内部使用的TabBar、TabBarButton，完成不规则的TabBar样式
    19. 1.19. AppDelegate.m实例化TabBarController
    20. 1.20. 找到TabBarController在什么时刻完成向内部TabBar添加TabBarButton的时刻
    21. 1.21. #小结
    22. 1.22. 所以知道了TabBarButton被添加的时刻。那么我们可以在此刻，将系统的TabBar对象替换成我们自己的定义的TabBar对象，让系统将后续的TabBarButton，添加到我们替换的TabBar对象上。
    23. 1.23. 修改MyTabBarControlelr，之前创建child controllers的代码，中间添加一个controller，这个控制器的item用来完成在tabBar上中间位置，添加不规则按钮
    24. 1.24. 接下来去我们自己定义的MyTabBar类，重写系统布局方法，在TabBar上添加一个自己的UIButton，并设置frame显示.
    25. 1.25. 对上述代码继续优化，当在TabBar添加中间的按钮时，但是不需要多一个UIViewController
    26. 1.26. #第一处修改、MyTabBarControlelr去掉添加中间item对应的ViewController
    27. 1.27. #第二处修改、MyTabBar，优化布局所有的tabBarButton

苹果KVC文档

https://developer.apple.com/library/prerelease/content/documentation/Cocoa/Conceptual/KeyValueCoding/Articles/BasicPrinciples.html#//apple_ref/doc/uid/20002170-BAJEAIEE

一切都建立在key-value coding 键值对

一个键值对字典表示一个类对象

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@{
@"name" : @"haha",
@"age" : @21，
}
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@Interface Person
@property NSString *name;
@property NSInteger age;
@end
@implementation Person
@end

应该说ObjectiveC类的对象是建立在key-value coding键值对的存储之上的。

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NSDictionary *dic = @{
@"person_001": @{
@"name" : @"xiaoming",
@"age" : @"19",
@"dogs" : @[
@{
@"dogId" : @"1",
@"name" : @"法国斗牛犬",
},
@{
@"dogId" : @"2",
@"name" : @"英国大丹犬",
},
],
@"cats" : @[
@{
@"catId" : @"1",
@"name" : @"咖啡毛",
},
@{
@"catId" : @"2",
@"name" : @"傻猫",
},
],

@"wife" : @{
@"name" : @"lili",
@"age" : @"19",
@"dogs" : @[
@{
@"dogId" : @"1",
@"name" : @"法国斗牛犬",
},
@{
@"dogId" : @"2",
@"name" : @"英国大丹犬",
},
],
@"cats" : @[
@{
@"catId" : @"1",
@"name" : @"咖啡毛",
},
@{
@"catId" : @"2",
@"name" : @"傻猫",
},
],
}
}
};

按照现在OO的思想，一个是Person类、一个Dog类、一个Cat类，但是最原始的数据组成就是一个key对应一个value的形式。

很显然使用OO单独划分出类之后，用他的对象去表示一个数据会让代码最复用，但是最终数据存储其实就是key-value的形式。

key 和 keyPath

key就是一个单个的key键，而keyPath是带有路径的key键。

对于上面是一个简单的key:

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id person = [dic valueForKey:@"person_001"];

如果是带有路径的key:

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NSString *name = [dic valueForKeyPath:@"person_001.name"];
NSString *age = [dic valueForKeyPath:@"person_001.age"];
NSArray *dogNames = [dic valueForKeyPath:@"person_001.dogs.name"];
NSArray *catIds = [dic valueForKeyPath:@"person_001.wife.cats.catId"];

输出结果

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(lldb) po name
xiaoming

(lldb) po age
19

(lldb) po dogNames
<__NSArrayI 0x17422d260>(
法国斗牛犬,
英国大丹犬
)


(lldb) po catIds
<__NSArrayI 0x17422d680>(
1,
2
)

完美运行，可以想象如果是取操作Person对象、Cat对象、Dog对象，然后遍历每一个子对象，取出每一个属性值，然后添加到一个mutable数组时，是那么的麻烦。

Getting Attribute Values Using Key-Value Coding

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valueForKey: 
valueForKeyPath:
valueForUndefinedKey: 如果没有对应key时调用的函数实现，默认是抛出NSUndefinedKeyException让程序崩溃
dictionaryWithValuesForKeys: 将对象的实例变量值转换成一个NSDictionary对象
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@interface KVCPerson : NSObject {
@package
NSString *_name;
NSInteger _age;
}
@end
@implementation KVCPerson
@end
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- (void)test10 {
KVCPerson *person = [KVCPerson new];
person->_age = 19;
person->_name = @"hahaha";
NSDictionary *dic = [person dictionaryWithValuesForKeys:@[@"age", @"name"]];
NSLog(@"dic = %@", dic);
}

输出结果

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2016-09-13 17:01:17.378 Demos[5568:441976] dic = {
age = 19;
name = hahaha;
}

苹果有一个Note注意提醒

  • (1) Collection objects, such as NSArray, NSSet, NSDictionary, can’t contain nil as a value

  • (2) Instead, you represent nil values using a special object, NSNull。 NSNull provides a single instance that represents the nil value for object properties

  • [NSNull null]
  • (id)kCFNull
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- (void)test10 {
KVCPerson *person = [KVCPerson new];
person->_age = 19;
person->_name = @"hahaha";
NSDictionary *dic = [person dictionaryWithValuesForKeys:@[@"age", @"name"]];
NSLog(@"dic = %@", dic);

[person setValue:[NSNull null] forKey:@"name"];
id retName = [person valueForKey:@"name"];
NSLog(@"name = %@, [name class] = %@", retName, [retName class]);
}

输出结果

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2016-09-13 17:10:31.666 Demos[5611:444225] dic = {
age = 19;
name = hahaha;
}
2016-09-13 17:10:31.669 Demos[5611:444225] name = <null>, [name class] = NSNull

Setting Attribute Values Using Key-Value Coding

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setValue:forKey:
setValue:forUndefinedKey: 没有key时执行的回调，默认实现也是抛出异常，直接程序崩溃
setValue:forKeyPath:
setValuesForKeysWithDictionary: 将一个字典对象通过KVC设置给NSObject对象对应的Ivar实例变量
setNilValueForKey: 当设置一个nil给对象的Ivar时被调用，默认实现就是抛异常让程序崩溃
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- (void)test10 {
KVCPerson *person = [KVCPerson new];
NSDictionary *dic = @{
@"name" : @"haha",
@"age" : @(19),
};
[person setValuesForKeysWithDictionary:dic];
NSLog(@"name = %@, age = %ld", person->_name, person->_age);
}

输出结果

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2016-09-13 17:17:39.351 Demos[5647:446041] name = haha, age = 19

重写KVCPerson的设置nil回调函数实现，防止崩溃并设置一个NSNull单例对象

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@interface KVCPerson : NSObject {
@package
NSString *_name;
NSInteger _age;
}
@end
@implementation KVCPerson
- (void)setNilValueForKey:(NSString *)key {
[self setValue:(id)kCFNull forKey:key];
}
@end
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- (void)test10 {
KVCPerson *person = [KVCPerson new];
NSDictionary *dic = @{
@"name" : @"haha",
@"age" : @(19),
};
[person setValuesForKeysWithDictionary:dic];
[person setNilValueForKey:@"name"];
NSLog(@"name = %@, age = %ld", person->_name, person->_age);
}

输出结果

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2016-09-13 17:27:17.865 Demos[5691:448651] name = <null>, age = 19

Key-Value Coding Accessor Methods

虽然可以直接使用Ivar进行赋值，但一般很少这么用，因为与实例变量Ivar内存布局有一定关系，大多时候都是给Ivar提供setter/getter方法实现来间接操作Ivar。

setValue:forKey: 的步骤:

  • (1) 根据key找到对应的Ivar
  • (2) 然后将value设置给Ivar

valueForKey:、valueForKeyPath: 的步骤:

  • (1) 根据key找到对应的Ivar
  • (2) 获取Ivar的值，并返回

一些简单实例变量的setter与getter就不写了。

主要记录下一些关于NSArray、NSSet实例变量的一些由编译器联想生成的快捷方法实现:

NSArray、NSSet Ivar Getter Indexed Accessors

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-countOf<Key>
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-objectIn<Key>AtIndex: or -<key>AtIndexes:
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-get<Key>:range:

下面是看下具体使用

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@interface KVCChildModel : NSString
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger price;
@end
@implementation KVCChildModel
- (NSString *)description {
return [NSString stringWithFormat:@"<%@-%p> _name = %@", [self class], self, _name];
}
- (NSString *)debugDescription {
return [self description];
}
@end
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@interface KVCModel : NSObject
@property (nonatomic, assign)       NSInteger arg1;
@property (nonatomic, copy)         NSString *arg2;
@property (nonatomic, strong)       NSArray *childModels;//to-many
@end
@implementation KVCModel

// 编译器联想生成的，只需要敲count即可
- (NSUInteger)countOfChildModels {
return _childModels.count;
}

// 编译器联想生成的，只需要敲objectIn即可
- (id)objectInChildModelsAtIndex:(NSUInteger)index {
if (index < _childModels.count) {
return [_childModels objectAtIndex:index];
}
return nil;
}

// 编译器联想生成的，只需要敲childModelsAt即可
- (NSArray *)childModelsAtIndexes:(NSIndexSet *)indexes {
return [_childModels objectsAtIndexes:indexes];
}

@end

测试代码

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- (void)test11 {
KVCModel *model = [KVCModel new];
NSMutableArray *childs = [NSMutableArray new];
for (NSInteger i = 0; i < 10; i++) {
KVCChildModel *child = [KVCChildModel new];
child.name = [NSString stringWithFormat:@"name_%ld", i];
[childs addObject:child];
}
model.childModels = childs;

NSUInteger count = [model countOfChildModels];
id obj = [model objectInChildModelsAtIndex:5];
NSArray *objs1 = [model childModelsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 5)]];

}

输出结果

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(lldb) po count
10

(lldb) po obj
<KVCChildModel-0x7ff2aa71cee0> _name = name_5

(lldb) po objs1
<__NSArrayI 0x7ff2aa7e11b0>(
<KVCChildModel-0x7ff2aa7e6080> _name = name_0,
<KVCChildModel-0x7ff2aa704070> _name = name_1,
<KVCChildModel-0x7ff2aa7c3120> _name = name_2,
<KVCChildModel-0x7ff2ac816c10> _name = name_3,
<KVCChildModel-0x7ff2aa7e2c60> _name = name_4
)

这些方法是编译器根据NSArray、NSSet属性实例变量自动联想生成的，我们可以按需去实现，不去实现也是没问题的。

NSMutableArray、NSMutableSet Ivar Mutable Indexed Accessors

  • insert….
  • add….

感觉都是一些比较鸡肋的方法实现.

@property声明的属性做了一些什么

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#import <Foundation/Foundation.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;

@end
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#import "Person.h"

@implementation Person

@end

那么@property (nonatomic, copy) NSString *name;其实就是包含如下:

  • (1) 生成了一个对象的实例成员变量
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NSString *_name;
  • (2) 生成了一个实例方法来修改成员变量的方法实现
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- (void)setName:(NSString *)name {
....
}
  • (3) 生成了一个实例方法来读取成员变量值的方法实现
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- (NSString *)name {
return _name;
}

也就是说访问实例变量（Ivar）的方式有两种:

  • (1) 间接操作: Ivar的setter/getter
  • (2) 直接操作: KVC键值对

但最终操作的都是对象的实例变量Ivar。

kvc设置对象的实例变量 与 调用对象属性方法 的区别

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@interface KVCModel : NSObject
@property (nonatomic, assign) NSInteger arg1;
@property (nonatomic, copy) NSString *arg2;
@end
@implementation KVCModel
- (NSString *)description {
return [NSString stringWithFormat:@"arg1 = %ld, arg2 = %@", _arg1, _arg2];
}
@end

@interface KVCViewController ()

@end

@implementation KVCViewController

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
[self test1];
}

- (void)test1 {
KVCModel *model = [KVCModel new];
model.arg1 = 19;
model.arg2 = @"haha";
NSLog(@"%@", [model description]);

[model setValue:@(20) forKey:@"arg1"];
[model setValue:@"hello" forKey:@"arg2"];
NSLog(@"%@", [model description]);
}

@end

输出结果

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2015-08-03 13:05:10.689 Demos[6455:420604] arg1 = 19, arg2 = haha
2015-08-03 13:05:10.690 Demos[6455:420604] arg1 = 20, arg2 = hello

可以看到其实使用KVC设置实例变量的值和调用属性setter实现的效果是有一样的。

将上面KVC访问实例变量的key改成如下:

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// 变量名前加一个 _
[model setValue:@(20) forKey:@"_arg1"];
[model setValue:@"hello" forKey:@"_arg2"];
NSLog(@"%@", [model description]);

程序运行效果仍然一样。那如果随便改一些了:

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[model setValue:@(20) forKey:@"xxxx"];
[model setValue:@"hello" forKey:@"yyyyy"];
NSLog(@"%@", [model description]);

程序运行后，走到如下代码时立刻崩溃:

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*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<KVCModel 0x7f99d8742b70> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key xxxx.'
*** First throw call stack:

提示没有从KVCModel对象中找到这样的一个key是xxxx。

KVC实际上是根据key查找Class中对应的Ivar，继而对找到的Ivar进行值的存取

  • (1) 首先使用arg1查询
  • (2) 如果第(1)没有找到实例变量，就继续使用_arg1查询实例变量
  • (3) 如果(1)与(2)都没有找到，就崩溃程序

使用KVC直接设置实例变量，绕过了@property实现的实例变量的内存管理、KVO通知、变量的读写权限。 一般情况下，不建议这么使用。

使用KVC修改私有成员变量Ivar的值

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@interface KVCModel : NSObject
@property (nonatomic, assign) NSInteger arg1;
@property (nonatomic, copy) NSString *arg2;
@end

@implementation KVCModel {
NSString *_arg3;//私有实例变量
}
- (NSString *)description {
return [NSString stringWithFormat:@"arg1 = %ld, arg2 = %@", _arg1, _arg2];
}
@end
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@implementation KVCViewController

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {    
[self test2];
}

- (void)test2 {
KVCModel *model = [KVCModel new];
[model setValue:@"hello" forKey:@"arg3"];
NSLog(@"私有实例变量arg3 = %@", [model valueForKey:@"arg3"]);
}

@end

运行结果

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2015-08-03 13:14:58.828 Demos[6598:460273] 私有实例变量arg3 = hello

可以看到完全是可以对私有的实例变量进行读写的。

还可以直接使用runtime函数，直接获取key对应的Ivar，进而进行实例变量值的存取

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- (void)test3 {
KVCModel *model = [KVCModel new];

///【重要】 如果使用运行时函数获取实例变量，一定要使用`_变量名`，必须和实例变量名保持一致
Ivar ivar = class_getInstanceVariable([model class], "_arg3");

object_setIvar(model, ivar, @"hello");

NSLog(@"私有实例变量arg3 = %@", object_getIvar(model, ivar));
}

运行结果

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2015-08-03 13:20:16.000 Demos[6728:485395] 私有实例变量arg3 = hello

但如果class_getInstanceVariable(cls, @"arg3")获取不到Ivar:

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- (void)test3 {
KVCModel *model = [KVCModel new];

/// 如果使用运行时函数获取实例变量，一定要使用`_变量名`，必须和实例变量名保持一致
Ivar ivar = class_getInstanceVariable([model class], "arg3");

object_setIvar(model, ivar, @"hello");
NSLog(@"私有实例变量arg3 = %@", object_getIvar(model, ivar));
}

输出

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2015-09-17 16:04:55.413 Demos[6187:40203] 私有实例变量arg3 = (null)

可见setValue:forKey:应该是先使用arg3查询Ivar，然后再使用_arg3查询Ivar。

所以我觉得setValue:forKey:的底层实现可能是利用runtime完成:

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- (void)setValue:(nullable id)value forKey:(NSString *)key {
//1. 
Class cls = [self class];

//2.
Ivar ivar = class_getInstanceVariable(cls, [key utf8String]);
if (!ivar) {
class_getInstanceVariable(cls, [NSString stringWithFormat:@"_%@", [key utf8String]]);
}

//3. 
object_setIvar(self, ivar, value);
}

那么对于objectForKey:实现就同理了。那么只有这样才能是通过key找到Class中对应的Ivar，继而对Ivar进行setter/getter。

key找不到时，处理异常

使用kvc时，如果代码中的key值不存在，会抛出异常。可以在类中通过重写它提供下面的这个方法来解决这个问题。

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- (void)setValue:(id)value forUndefinedKey:(NSString *)key;
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@interface KVCModel : NSObject
@property (nonatomic, assign) NSInteger arg1;
@property (nonatomic, copy) NSString *arg2;
@end

@implementation KVCModel {
NSString *_arg3;//私有实例变量
}

- (NSString *)description {
return [NSString stringWithFormat:@"arg1 = %ld, arg2 = %@", _arg1, _arg2];
}

- (void)setValue:(id)value forUndefinedKey:(NSString *)key {
NSLog(@"不存在的key");
}

@end
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@implementation KVCViewController

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
[self test4];
}

- (void)test4 {
KVCModel *model = [KVCModel new];
[model setValue:@"hello" forKey:@"xxxx"];
}

@end

运行结果

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2015-08-03 13:24:24.071 Demos[6827:509952] 不存在的key

KVC键值对赋值提供两种方式

  • 第一种: setValue:forKey:简单形读写，实例变量没有层级的

  • 第二种: setValue:forKeyPath:复杂形读写，实例变量有多层级关系的（结合对象、自定义对象…等）

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@interface KVCChildModel : NSString
@property (nonatomic, copy) NSString *name;
@end
@implementation KVCChildModel
@end
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@interface KVCModel : NSObject
@property (nonatomic, assign) NSInteger arg1;
@property (nonatomic, copy) NSString *arg2;
@property (nonatomic, strong) KVCChildModel *childModel;
@property (nonatomic, strong) NSArray *childModels;
@end

@implementation KVCModel {
NSString *_arg3;//私有实例变量
}

- (NSString *)description {
return [NSString stringWithFormat:@"arg1 = %ld, arg2 = %@", _arg1, _arg2];
}

- (void)setValue:(id)value forUndefinedKey:(NSString *)key {
NSLog(@"不存在的key");
}

@end
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@implementation KVCViewController

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
[self test5];
}

- (void)test5 {

KVCModel *model = [KVCModel new];
model.arg1 = 19;
model.arg2 = @"xiongzenghui001";

KVCChildModel *child = [KVCChildModel new];
child.name = @"xiongzenghui002";
model.childModel = child;

NSMutableArray *childs = [NSMutableArray new];
for (NSInteger i = 0; i < 3; i++) {
KVCChildModel *child = [KVCChildModel new];
child.name = [NSString stringWithFormat:@"xiongzenghui00%ld", (i+3)];
[childs addObject:child];
}
model.childModels = [childs copy];

//1.
KVCChildModel *tmpModel = [model valueForKey:@"childModel"];
NSLog(@"tmpModel.name = %@", tmpModel.name);

//2.
NSArray *tmpModels = [model valueForKey:@"childModels"];
for (KVCChildModel *model in tmpModels) {
NSLog(@"model.name = %@", model.name);
}

/**
*  上面是获取KVCModel对象的第一级实例变量值，但是如果想继续获取得到的变量值它下面的其他变量值了？
*/

//3. 会导致崩溃的错误代码
//    NSLog(@"%@", [model valueForKey:@"childModel.name"]);
//    NSArray *names = [model valueForKey:@"childModels.name"];

//4. 正确应该是带有路径的KVC函数
NSLog(@"%@", [model valueForKeyPath:@"childModel.name"]);
NSArray *names = [model valueForKeyPath:@"childModels.name"];
for (NSString *name in names) {
NSLog(@"name = %@", name);
};
}

@end

运行结果

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2016-08-03 13:45:04.970 Demos[8226:574663] tmpModel.name = xiongzenghui002
2016-08-03 13:45:04.970 Demos[8226:574663] model.name = xiongzenghui003
2016-08-03 13:45:04.970 Demos[8226:574663] model.name = xiongzenghui004
2016-08-03 13:45:04.971 Demos[8226:574663] model.name = xiongzenghui005
2016-08-03 13:45:04.971 Demos[8226:574663] xiongzenghui002
2016-08-03 13:45:04.971 Demos[8226:574663] name = xiongzenghui003
2016-08-03 13:45:04.971 Demos[8226:574663] name = xiongzenghui004
2016-08-03 13:45:04.971 Demos[8226:574663] name = xiongzenghui005

那么针对setValue:forKeyPath:使用和上面是一样的。

小结使用forKey:和forKeyPath:区别:

  • forKey:只能对单个路径的key设置value
  • forKeyPath:包含forKey:，单个路径的key设置value
  • forKeyPath:更加可以针对多个路径的key设置value，路径使用.来分开

使用valueForKeyPath:直接读取一个对象的数组内每一个对象的变量值，并进行基本运算

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@interface KVCChildModel : NSString
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger price;
@end
@implementation KVCChildModel
@end
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@interface KVCModel : NSObject
@property (nonatomic, assign) NSInteger arg1;
@property (nonatomic, copy) NSString *arg2;
@property (nonatomic, strong) KVCChildModel *childModel;
@property (nonatomic, strong) NSArray *childModels;
@end

@implementation KVCModel {
NSString *_arg3;//私有实例变量
}

- (NSString *)description {
return [NSString stringWithFormat:@"arg1 = %ld, arg2 = %@", _arg1, _arg2];
}

- (void)setValue:(id)value forUndefinedKey:(NSString *)key {
NSLog(@"不存在的key");
}

@end
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@implementation KVCViewController

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
[self test6];
}

- (void)test6 {

KVCModel *model = [KVCModel new];
model.arg1 = 19;
model.arg2 = @"xiongzenghui001";

NSMutableArray *childs = [NSMutableArray new];
for (NSInteger i = 0; i < 3; i++) {
KVCChildModel *child = [KVCChildModel new];
child.name = [NSString stringWithFormat:@"xiongzenghui00%ld", (i+3)];
child.price = (i + 1) * (rand() % 100);
NSLog(@"child.price = %ld", child.price);
[childs addObject:child];
}
model.childModels = [childs copy];

// 直接对keyPath中的数组中所有对象的price求和
NSInteger totoalPrice = [[model valueForKeyPath:@"childModels.@sum.price"] integerValue];
NSLog(@"totoalPrice = %ld", totoalPrice);
}

@end

运行结果

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2016-08-03 13:52:21.145 Demos[8349:614432] child.price = 7
2016-08-03 13:52:21.146 Demos[8349:614432] child.price = 98
2016-08-03 13:52:21.146 Demos[8349:614432] child.price = 219
2016-08-03 13:52:21.146 Demos[8349:614432] totoalPrice = 324

直接对数组内所有对象的某一个属性变量进行运算，还有如下这些:

  • @count: 返回一个值为集合中对象总数的NSNumber对象。
  • @sum: 首先把集合中的每个对象都转换为double类型，然后计算其总，最后返回一个值为这个总和的NSNumber对象。
  • @avg: Takes the double value of each object in the collection, and returns the average value as an NSNumber.
  • @max: 使用compare:方法来确定最大值。所以为了让其正常工作，集合中所有的对象都必须支持和另一个对象的比较。
  • @min: 和@max一样，但是返回的是集合中的最小值。
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NSLog(@"show: 数组中总成绩SUMscore = %@",[self.testAry valueForKeyPath:@"@sum.score"] );
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NSLog(@"show2: 数组中平均成绩AVGscore = %@",[self.testAry valueForKeyPath:@"@avg.score"] );
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NSLog(@"show2: 数组中最大成绩MAXscore = %@",[self.testAry valueForKeyPath:@"@max.score"] );
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NSLog(@"show2: 数组中最小成绩MINscore = %@",[self.testAry valueForKeyPath:@"@min.score"] );

对一个数组，@unionOfObjects / @distinctUnionOfObjects 运算符

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NSArray *inventory = @[iPhone5, iPhone5, iPhone5, iPadMini, macBookPro, macBookPro];
  • @unionOfObjects 效果
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[inventory valueForKeyPath:@"@unionOfObjects.name"]; 

结果: "iPhone 5", "iPhone 5", "iPhone 5", "iPad Mini", "MacBook Pro", "MacBook Pro"
  • @distinctUnionOfObjects 效果
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[inventory valueForKeyPath:@"@distinctUnionOfObjects.name"]; 

结果: "iPhone 5", "iPad Mini", "MacBook Pro"

dictionaryWithValuesForKeys:/setValuesForKeysWithDictionary: ，对象与字典之间的快速转换

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@interface KVCChildModel : NSString
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger price;
@end
@implementation KVCChildModel
@end
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- (void)test7 {
KVCChildModel *model = [KVCChildModel new];

NSDictionary *dict = @{
@"name" : @"xiongzenghui",
@"price" : @300,
};

[model setValuesForKeysWithDictionary:dict];

NSLog(@"model.name = %@", model.name);
NSLog(@"model.price = %ld", model.price);
}

运行结果

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2016-08-03 18:51:32.539 Demos[37574:2366999] model.name = xiongzenghui
2016-08-03 18:51:32.539 Demos[37574:2366999] model.price = 300
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- (void)test8 {
KVCChildModel *model = [KVCChildModel new];
model.name = @"xiongzenghui";
model.price = 300;

NSDictionary * dic = [model dictionaryWithValuesForKeys:@[@"name", @"price"]];
NSLog(@"dic = %@", dic);
}

运行结果

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2016-08-03 18:53:40.219 Demos[37700:2380520] dic = {
name = xiongzenghui;
price = 300;
}

使用KVC替换TabBarController内部使用的TabBar、TabBarButton，完成不规则的TabBar样式

此方法需要给不规则按钮项，添加一个对应的RootViewController实例。也可以不用添加一个RootViewController，只是作为一个触发事件源.

AppDelegate.m实例化TabBarController

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- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

UIWindow *window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
self.window = window;

MyTabBarControlelr *tabVC= [[MyTabBarControlelr alloc] init];
self.window.rootViewController = tabVC;

self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];

return YES;
}

找到TabBarController在什么时刻完成向内部TabBar添加TabBarButton的时刻

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@interface MyTabBarControlelr : UITabBarController

@end
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#import "MyTabBarControlelr.h"
#import <objc/message.h>

@implementation MyTabBarControlelr

- (void)viewWillAppear:(BOOL)animated {

NSLog(@"viewWillAppear之前, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);

[super viewWillAppear:animated];

NSLog(@"viewWillAppear之后, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);
}

- (void)viewDidLoad {


NSLog(@"viewDidLoad之前, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);

[super viewDidLoad];

[self setupChildViewControllers];

NSLog(@"viewDidLoad之后, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);
}

- (void)setupChildViewControllers {

UIViewController *vc1 = [[UIViewController alloc] init];
vc1.view.backgroundColor = [UIColor redColor];
vc1.tabBarItem.title=@"1";

UIViewController *vc2 = [[UIViewController alloc] init];
vc2.view.backgroundColor = [UIColor blueColor];
vc2.tabBarItem.title=@"2";

//用来在tabBar中间添加按钮的
UIViewController *vc3 = [[UIViewController alloc] init];
vc3.view.backgroundColor = [UIColor yellowColor];
//如果中间没有对应的ViewController，就不用添加

UIViewController *vc4 = [[UIViewController alloc] init];
vc4.view.backgroundColor = [UIColor grayColor];
vc4.tabBarItem.title=@"4";

UIViewController *vc5 = [[UIViewController alloc] init];
vc5.view.backgroundColor = [UIColor purpleColor];
vc5.tabBarItem.title=@"5";

[self addChildViewController:vc1];
[self addChildViewController:vc2];
[self addChildViewController:vc3];
[self addChildViewController:vc4];
[self addChildViewController:vc5];
}

@end

控制台输出如下

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2016-04-05 12:21:30.387 CustomTabBar[41675:155007] viewDidLoad之前, tabbarVC.tabbar = <UITabBar: 0x7fb3c86b4010; frame = (0 519; 320 49); autoresize = W+TM; layer = <CALayer: 0x7fb3c86b4340>>, tabbarVC.tabbar.subviews = (
)
2016-04-05 12:21:30.389 CustomTabBar[41675:155007] viewDidLoad之后, tabbarVC.tabbar = <UITabBar: 0x7fb3c86b4010; frame = (0 519; 320 49); autoresize = W+TM; layer = <CALayer: 0x7fb3c86b4340>>, tabbarVC.tabbar.subviews = (
)
2016-04-05 12:21:30.394 CustomTabBar[41675:155007] viewWillAppear之前, tabbarVC.tabbar = <UITabBar: 0x7fb3c86b4010; frame = (0 519; 320 49); autoresize = W+TM; layer = <CALayer: 0x7fb3c86b4340>>, tabbarVC.tabbar.subviews = (
)
2016-04-05 12:21:30.399 CustomTabBar[41675:155007] viewWillAppear之后, tabbarVC.tabbar = <UITabBar: 0x7fb3c86b4010; frame = (0 519; 320 49); autoresize = W+TM; layer = <CALayer: 0x7fb3c86b4340>>, tabbarVC.tabbar.subviews = (
"<UITabBarButton: 0x7fb3c8720060; frame = (2 1; 60 48); opaque = NO; layer = <CALayer: 0x7fb3c8721a50>>",
"<UITabBarButton: 0x7fb3c8724cb0; frame = (66 1; 60 48); opaque = NO; layer = <CALayer: 0x7fb3c8724b80>>",
"<UITabBarButton: 0x7fb3c8726010; frame = (130 1; 60 48); opaque = NO; layer = <CALayer: 0x7fb3c8726270>>",
"<UITabBarButton: 0x7fb3c87269a0; frame = (194 1; 60 48); opaque = NO; layer = <CALayer: 0x7fb3c8718500>>",
"<UITabBarButton: 0x7fb3c8727ec0; frame = (258 1; 60 48); opaque = NO; layer = <CALayer: 0x7fb3c8727790>>"
)

可以得到如果执行[super viewWillAppear:animated]就会完成向TabBar添加TabBarButton。

#小结

  • 在viewDidLoad时，
  • TabBarController只会完成添加TabBar的工作

  • 而不会完成添加TabBarButton的工作

  • 而在viewWillAppear时

  • 执行[super viewWillAppear:animated]之后，TabBarController才会完成添加TabBarButton
  • 因为完成添加TabBarButton的代码，是系统提供的父类完成的

所以知道了TabBarButton被添加的时刻。那么我们可以在此刻，将系统的TabBar对象替换成我们自己的定义的TabBar对象，让系统将后续的TabBarButton，添加到我们替换的TabBar对象上。

为什么要替换系统的UITabBar？ 因为系统的UITabBar对加上的UITabBarButton的布局frame是不能再修改的，也就是UITabBar里面的layoutSunviews方法无法控制器其执行。

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#import <UIKit/UIKit.h>

@interface MyTabBarControlelr : UITabBarController

@end
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#import "MyTabBarControlelr.h"
#import <objc/message.h>

#import "MyTabBar.h"

@interface MyTabBarControlelr ()

@property (nonatomic, strong) MyTabBar *myTabBar;

@end

@implementation MyTabBarControlelr

- (MyTabBar *)myTabBar {
if (!_myTabBar) {
_myTabBar = [[MyTabBar alloc] init];
}
return _myTabBar;
}

- (void)viewWillAppear:(BOOL)animated {

NSLog(@"viewWillAppear之前, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);

// 替换掉系统使用的tabBar
{
//2.1 使用KVC替换（会编译成如下消息代码）
[self setValue:self.myTabBar forKeyPath:@"tabBar"];

//2.2 直接使用消息代码，向当前控制器对象，发送一个消息，寻找SEL为@selector(setTabBar:)的方法实现
//objc_msgSend(self, @selector(setTabBar:), self.myTabBar);
}

[super viewWillAppear:animated];

NSLog(@"viewWillAppear之后, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);
}

- (void)viewDidLoad {


NSLog(@"viewDidLoad之前, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);

[super viewDidLoad];

[self setupChildViewControllers];

NSLog(@"viewDidLoad之后, tabbarVC.tabbar = %@, tabbarVC.tabbar.subviews = %@\n", self.tabBar, self.tabBar.subviews);
}

- (void)setupChildViewControllers {

UIViewController *vc1 = [[UIViewController alloc] init];
vc1.view.backgroundColor = [UIColor redColor];
vc1.tabBarItem.title=@"1";

UIViewController *vc2 = [[UIViewController alloc] init];
vc2.view.backgroundColor = [UIColor blueColor];
vc2.tabBarItem.title=@"2";

//用来在tabBar中间添加按钮的
UIViewController *vc3 = [[UIViewController alloc] init];
vc3.view.backgroundColor = [UIColor yellowColor];
//如果中间没有对应的ViewController，就不用添加

UIViewController *vc4 = [[UIViewController alloc] init];
vc4.view.backgroundColor = [UIColor grayColor];
vc4.tabBarItem.title=@"4";

UIViewController *vc5 = [[UIViewController alloc] init];
vc5.view.backgroundColor = [UIColor purpleColor];
vc5.tabBarItem.title=@"5";

[self addChildViewController:vc1];
[self addChildViewController:vc2];
[self addChildViewController:vc3];
[self addChildViewController:vc4];
[self addChildViewController:vc5];
}

@end

修改MyTabBarControlelr，之前创建child controllers的代码，中间添加一个controller，这个控制器的item用来完成在tabBar上中间位置，添加不规则按钮

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- (void)setupChildViewControllers {

UIViewController *vc1 = [[UIViewController alloc] init];
vc1.view.backgroundColor = [UIColor redColor];
vc1.tabBarItem.title=@"1";

UIViewController *vc2 = [[UIViewController alloc] init];
vc2.view.backgroundColor = [UIColor blueColor];
vc2.tabBarItem.title=@"2";

//修改，用来在tabBar中间添加按钮的
UIViewController *vc3 = [[UIViewController alloc] init];
vc3.view.backgroundColor = [UIColor yellowColor];

UIViewController *vc4 = [[UIViewController alloc] init];
vc4.view.backgroundColor = [UIColor grayColor];
vc4.tabBarItem.title=@"4";

UIViewController *vc5 = [[UIViewController alloc] init];
vc5.view.backgroundColor = [UIColor purpleColor];
vc5.tabBarItem.title=@"5";

[self addChildViewController:vc1];
[self addChildViewController:vc2];
[self addChildViewController:vc3];
[self addChildViewController:vc4];
[self addChildViewController:vc5];
}

接下来去我们自己定义的MyTabBar类，重写系统布局方法，在TabBar上添加一个自己的UIButton，并设置frame显示.

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#import "MyTabBar.h"

@interface MyTabBar ()

/**
*  添加在TabBar中间位置的不规则按钮
*/
@property (nonatomic, strong) UIButton *middleButton;

@end
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@implementation MyTabBar

- (UIButton *)middleButton {
if (!_middleButton) {

_middleButton = [UIButton buttonWithType:UIButtonTypeCustom];
[_middleButton addTarget:self action:@selector(middleClick:) forControlEvents:UIControlEventTouchUpInside];

UIImage *img = [UIImage imageNamed:@"middle"];
[_middleButton setImage:img forState:UIControlStateNormal];

//让按钮的大小随背景图片大小
[_middleButton sizeToFit];
}
return _middleButton;
}

- (void)layoutSubviews {

//1. 先执行系统UITabbar的布局UITabBarButton的代码
[super layoutSubviews];

//2. 完成按钮添加布局
CGFloat imageH = self.middleButton.currentImage.size.height;
CGFloat imageW = self.middleButton.currentImage.size.width;
CGFloat topInset = imageH - self.bounds.size.height;

//将不规则按钮添加到TabBar中间的位置
[self addSubview:self.middleButton];

self.middleButton.frame = CGRectMake(CGRectGetMidX(self.bounds) - imageW/2.0,
-topInset,
imageW,
imageH);

}


- (void)middleClick:(id)sender {

}

@end

对上述代码继续优化，当在TabBar添加中间的按钮时，但是不需要多一个UIViewController

#第一处修改、MyTabBarControlelr去掉添加中间item对应的ViewController

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@implementation MyTabBarControlelr

- (void)setupChildViewControllers {

UIViewController *vc1 = [[UIViewController alloc] init];
vc1.view.backgroundColor = [UIColor redColor];
vc1.tabBarItem.title=@"1";

UIViewController *vc2 = [[UIViewController alloc] init];
vc2.view.backgroundColor = [UIColor blueColor];
vc2.tabBarItem.title=@"2";

//用来在tabBar中间添加按钮的
//    UIViewController *vc3 = [[UIViewController alloc] init];
//    vc3.view.backgroundColor = [UIColor yellowColor];
//如果中间没有对应的ViewController，就不用添加

UIViewController *vc4 = [[UIViewController alloc] init];
vc4.view.backgroundColor = [UIColor grayColor];
vc4.tabBarItem.title=@"4";

UIViewController *vc5 = [[UIViewController alloc] init];
vc5.view.backgroundColor = [UIColor purpleColor];
vc5.tabBarItem.title=@"5";

[self addChildViewController:vc1];
[self addChildViewController:vc2];
//    [self addChildViewController:vc3];
[self addChildViewController:vc4];
[self addChildViewController:vc5];
}

@end

#第二处修改、MyTabBar，优化布局所有的tabBarButton

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#import <UIKit/UIKit.h>

@interface RDTabBar : UITabBar

@end
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#import "RDTabBar.h"

@interface RDTabBar ()

@property (nonatomic, strong) UIButton *middleButton;

@end

@implementation RDTabBar

- (UIButton *)middleButton {
if (!_middleButton) {

_middleButton = [UIButton buttonWithType:UIButtonTypeCustom];
[_middleButton addTarget:self action:@selector(middleClick:) forControlEvents:UIControlEventTouchUpInside];

UIImage *img = [UIImage imageNamed:@"tabBar_publish_icon"];
[_middleButton setImage:img forState:UIControlStateNormal];

//让按钮的大小随背景图片大小
[_middleButton sizeToFit];
}
return _middleButton;
}

- (void)layoutSubviews {
[super layoutSubviews];
[self layoutOtherNomalItem];
[self layoutMiddleButton];
}

- (void)layoutOtherNomalItem {

CGFloat x = 0;
CGFloat y = 0;
CGFloat w = self.bounds.size.width / (self.items.count + 1);
CGFloat h = self.bounds.size.height;

NSInteger middleIndex = (self.items.count + 1) / 2;

NSInteger index = 0;

for (UIView *subView in self.subviews) {
if ([subView isKindOfClass:NSClassFromString(@"UITabBarButton")]) {
CGRect frame = CGRectMake(x + index * w,
y,
w,
h);
subView.frame = frame;
index++;
if (index == middleIndex) {
index++;
}
}
}
}

- (void)layoutMiddleButton {

CGFloat imageH = self.middleButton.currentImage.size.height;
CGFloat imageW = self.middleButton.currentImage.size.width;
CGFloat topInset = imageH - self.bounds.size.height;

[self addSubview:self.middleButton];

self.middleButton.frame = CGRectMake(CGRectGetMidX(self.bounds) - imageW/2.0,
-topInset,
imageW,
imageH);
}

- (void)middleClick:(id)sender {

}

@end

如上就是不需要给中间按钮添加一个对应的UIViewController对象到TabBarController的实现.

Contents
  1. 1. 苹果KVC文档
    1. 1.1. 一切都建立在key-value coding 键值对
    2. 1.2. key 和 keyPath
    3. 1.3. Getting Attribute Values Using Key-Value Coding
    4. 1.4. Setting Attribute Values Using Key-Value Coding
    5. 1.5. Key-Value Coding Accessor Methods
    6. 1.6. NSArray、NSSet Ivar Getter Indexed Accessors
    7. 1.7. NSMutableArray、NSMutableSet Ivar Mutable Indexed Accessors
    8. 1.8. @property声明的属性做了一些什么
    9. 1.9. kvc设置对象的实例变量 与 调用对象属性方法 的区别
    10. 1.10. KVC实际上是根据key查找Class中对应的Ivar，继而对找到的Ivar进行值的存取
    11. 1.11. 使用KVC修改私有成员变量Ivar的值
    12. 1.12. 还可以直接使用runtime函数，直接获取key对应的Ivar，进而进行实例变量值的存取
    13. 1.13. 所以我觉得setValue:forKey:的底层实现可能是利用runtime完成:
    14. 1.14. key找不到时，处理异常
    15. 1.15. KVC键值对赋值提供两种方式
    16. 1.16. 使用valueForKeyPath:直接读取一个对象的数组内每一个对象的变量值，并进行基本运算
    17. 1.17. dictionaryWithValuesForKeys:/setValuesForKeysWithDictionary: ，对象与字典之间的快速转换
    18. 1.18. 使用KVC替换TabBarController内部使用的TabBar、TabBarButton，完成不规则的TabBar样式
    19. 1.19. AppDelegate.m实例化TabBarController
    20. 1.20. 找到TabBarController在什么时刻完成向内部TabBar添加TabBarButton的时刻
    21. 1.21. #小结
    22. 1.22. 所以知道了TabBarButton被添加的时刻。那么我们可以在此刻，将系统的TabBar对象替换成我们自己的定义的TabBar对象，让系统将后续的TabBarButton，添加到我们替换的TabBar对象上。
    23. 1.23. 修改MyTabBarControlelr，之前创建child controllers的代码，中间添加一个controller，这个控制器的item用来完成在tabBar上中间位置，添加不规则按钮
    24. 1.24. 接下来去我们自己定义的MyTabBar类，重写系统布局方法，在TabBar上添加一个自己的UIButton，并设置frame显示.
    25. 1.25. 对上述代码继续优化，当在TabBar添加中间的按钮时，但是不需要多一个UIViewController
    26. 1.26. #第一处修改、MyTabBarControlelr去掉添加中间item对应的ViewController
    27. 1.27. #第二处修改、MyTabBar，优化布局所有的tabBarButton