动态获取属性

动态获取属性变量名, 类型, atomic/nonatomic, strong/weak/copy/retain/assgn, read
相关函数:

  • objc_getClass or [self class] 获取类
  • class_copyIvarList 获取变量列表
  • ivar_getName 获取变量名称
  • ivar_getTypeEncoding 获取变量相关类型属性, 通过 Type encoding 表示. Type Coding
  • class_getProperty
  • property_getName
  • property_getAttributes
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/** 
 * Describes the instance variables declared by a class.
 * 
 * @param cls The class to inspect.
 * @param outCount On return, contains the length of the returned array. 
 *  If outCount is NULL, the length is not returned.
 * 
 * @return An array of pointers of type Ivar describing the instance variables declared by the class. 
 *  Any instance variables declared by superclasses are not included. The array contains *outCount 
 *  pointers followed by a NULL terminator. You must free the array with free().
 * 
 *  If the class declares no instance variables, or cls is Nil, NULL is returned and *outCount is 0.
 */
OBJC_EXPORT Ivar *class_copyIvarList(Class cls, unsigned int *outCount) 
     OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);

通过 class_copyIvarList 函数获取 Ivar 变量. 该函数返回一个 Ivar 数组.

需要注意的是, 该函数只显示当前类的变量, 父类的不显示. 如果当前类没有定义属性变量, 或者输入的 cls 为 Nil, 返回的 *outcount 值为0.

若要获取包含父类的所有成员变量, 可以参考 MJExtension 的实现, 代码在 NSObject+MJMember.h 文件中.

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/**
 *  遍历所有的成员变量
 */
- (void)enumerateIvarsWithBlock:(MJIvarsBlock)block;

回到主题, 获取到 Ivar 之后, 通过 ivar_getName 可以获取到变量的名称, 使用自动合成属性时变量名前会加入下划线 _.

使用 ivar_getTypeEncoding 获取变量的类型, NSFoundation对象返回的字符串是其类型名, 如 “NSNumber” 类型的变量, 则返回 @"NSNumber".

其他返回类型使用 Type Coding
.

Code Meaning
c A char
i An int
s A short
l A long
q A long long
C An unsigned char
I An unsigned int
S An unsigned short
L An unsigned long
Q An unsigned long long
f A float
d A double
B A C++ bool or a C99 _Bool
v A void
* A character string (char *)
@ An object (whether statically typed or typed id)
# A class object (Class)
: A method selector (SEL)
[array type] An array
{name=type…} A structure
(name=type…) A union
bnum A bit field of num bits
^type A pointer to type
? An unknown type (among other things, this code is used for function pointers)