[OC Runtime编程指南_翻译]一、介绍 & 二、运行时版本和平台
[OC Runtime编程指南_翻译]三、与运行时交互
[OC Runtime编程指南_翻译]四、消息传递
[OC Runtime编程指南_翻译]五、动态方法解析
[OC Runtime编程指南_翻译]六、消息转发
[OC Runtime编程指南_翻译]七、类型编码
[OC Runtime编程指南_翻译]八、声明属性注:pdf翻译文档百度云下载链接,密码:zcs2
当编译器遇到属性声明(请参阅 _Objective-C _编程语言中 声明属性)时,它会生成与封闭类、类别或协议相关联的描述性元数据。您可以使用支持在类或协议上按名称查找属性、以**@encode
**字符串形式获取属性类型以及以C字符串数组形式复制属性属性列表的函数来访问此元数据。声明的属性列表可用于每个类和协议
。
属性类型和功能
**Property
**结构定义属性描述符的不透明句柄。
typedef struct objc_property *Property;
可以使用函数**class_copyPropertyList
和protocol_copyPropertyList
**分别检索与类
(包括加载的类别)和协议
相关联的属性数组
:
objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)
objc_property_t *protocol_copyPropertyList(Protocol *proto, unsigned int *outCount)
例如,给定以下类声明:
@interface Lender : NSObject {
float alone;
}
@property float alone;
@end
可以使用以下方法获取属性列表
:
id LenderClass = objc_getClass("Lender");
unsigned int outCount;
objc_property_t *properties = class_copyPropertyList(LenderClass, &outCount);
您可以使用 **property_getName
**函数来发现属性的名称
:
const char *property_getName(objc_property_t property)
可以使用函数**class_getProperty
和protocol_getProperty
**分别获取对类和协议中给定名称的属性的引用
:
objc_property_t class_getProperty(Class cls, const char *name)
objc_property_t protocol_getProperty(Protocol *proto, const char *name, BOOL isRequiredProperty, BOOL isInstanceProperty)
可以使用**property_getAttributes
函数来发现属性的名称和@encode
** type字符串。有关编码类型字符串的详细信息,请参阅 类型编码;有关此字符串的详细信息,请参阅 Property Type String和 Property Attribute Description Examples。
const char *property_getAttributes(objc_property_t property)
将这些组合在一起,可以使用以下代码打印与类关联的所有属性的列表:
id LenderClass = objc_getClass("Lender");
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(LenderClass, &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
fprintf(stdout, "%s %s\n", property_getName(property), property_getAttributes(property));
}
属性类型字符串
可以使用**property_getAttributes
函数来发现属性的名称、@encode
** type字符串以及属性的其他属性。
字符串以**T
开头,后跟@encode
类型和逗号
,以V
**结尾,后跟支持实例变量的名称
。其中,属性由以下描述符指定,用逗号分隔:
Table 7-1 声明的属性类型编码
Code | Meaning |
---|---|
R | The property is read-only (readonly).属性为只读(只读)。 |
C | The property is a copy of the value last assigned (copy). |
& | The property is a reference to the value last assigned (retain). |
N | The property is non-atomic (nonatomic). |
G | The property defines a custom getter selector name. The name follows the G (for example, GcustomGetter,). |
S | The property defines a custom setter selector name. The name follows the S (for example, ScustomSetter:,). |
D | The property is dynamic (@dynamic). |
W | The property is a weak reference (__weak). |
P | The property is eligible for garbage collection. |
t | Specifies the type using old-style encoding. |
示例, 请参见 Property Attribute Description Examples.
Property Attribute 描述示例
根据这些定义:
enum FooManChu { FOO, MAN, CHU };
struct YorkshireTeaStruct { int pot; char lady; };
typedef struct YorkshireTeaStruct YorkshireTeaStructType;
union MoneyUnion { float alone; double down; };
下表显示了示例属性声明和属性**property_getAttributes
**返回的相应字符串:
Property declaration | Property description |
---|---|
@property char charDefault; | Tc,VcharDefault |
@property double doubleDefault; | Td,VdoubleDefault |
@property enum FooManChu enumDefault; | Ti,VenumDefault |
@property float floatDefault; | Tf,VfloatDefault |
@property int intDefault; | Ti,VintDefault |
@property long longDefault; | Tl,VlongDefault |
@property short shortDefault; | Ts,VshortDefault |
@property signed signedDefault; | Ti,VsignedDefault |
@property struct YorkshireTeaStruct structDefault; | T{YorkshireTeaStruct="pot"i"lady"c},VstructDefault |
@property YorkshireTeaStructType typedefDefault; | T{YorkshireTeaStruct="pot"i"lady"c},VtypedefDefault |
@property union MoneyUnion unionDefault; | T(MoneyUnion="alone"f"down"d),VunionDefault |
@property unsigned unsignedDefault; | TI,VunsignedDefault |
@property int (*functionPointerDefault)(char *); | T^?,VfunctionPointerDefault |
@property id idDefault; | |
Note: the compiler warns: “no ‘assign’, ‘retain’, or ‘copy’ attribute is specified - ‘assign’ is assumed” | T@,VidDefault |
@property int *intPointer; | T^i,VintPointer |
@property void *voidPointerDefault; | T^v,VvoidPointerDefault |
@property int intSynthEquals; In the implementation block: @synthesize intSynthEquals=_intSynthEquals; | Ti,V_intSynthEquals |
@property(getter=intGetFoo, setter=intSetFoo:) int intSetterGetter; | Ti,GintGetFoo,SintSetFoo:,VintSetterGetter |
@property(readonly) int intReadonly; | Ti,R,VintReadonly |
@property(getter=isIntReadOnlyGetter, readonly) int intReadonlyGetter; | Ti,R,GisIntReadOnlyGetter |
@property(readwrite) int intReadwrite; | Ti,VintReadwrite |
@property(assign) int intAssign; | Ti,VintAssign |
@property(retain) id idRetain; | T@,&,VidRetain |
@property(copy) id idCopy; | T@,C,VidCopy |
@property(nonatomic) int intNonatomic; | Ti,VintNonatomic |
@property(nonatomic, readonly, copy) id idReadonlyCopyNonatomic; | T@,R,C,VidReadonlyCopyNonatomic |
@property(nonatomic, readonly, retain) id idReadonlyRetainNonatomic; | T@,R,&,VidReadonlyRetainNonatomic |