第一种:runtime.h里的方法
BOOL class_addProperty(Class cls,
const char *name,
const objc_property_attribute_t *attributes,
unsigned int attributeCount)
输出:#include <objc/runtime.h> #import <Foundation/Foundation.h> @interface SomeClass : NSObject { NSString *_privateName; } @end @implementation SomeClass - (id)init { self = [super init]; if (self) _privateName = @"Steve"; return self; } @end NSString *nameGetter(id self, SEL _cmd) { Ivar ivar = class_getInstanceVariable([SomeClass class], "_privateName"); return object_getIvar(self, ivar); } void nameSetter(id self, SEL _cmd, NSString *newName) { Ivar ivar = class_getInstanceVariable([SomeClass class], "_privateName"); id oldName = object_getIvar(self, ivar); if (oldName != newName) object_setIvar(self, ivar, [newName copy]); } int main(void) { @autoreleasepool { objc_property_attribute_t type = { "T", "@"NSString"" }; objc_property_attribute_t ownership = { "C", "" }; // C = copy objc_property_attribute_t backingivar = { "V", "_privateName" }; objc_property_attribute_t attrs[] = { type, ownership, backingivar }; class_addProperty([SomeClass class], "name", attrs, 3); class_addMethod([SomeClass class], @selector(name), (IMP)nameGetter, "@@:"); class_addMethod([SomeClass class], @selector(setName:), (IMP)nameSetter, "v@:@"); id o = [SomeClass new]; NSLog(@"%@", [o name]); [o setName:@"Jobs"]; NSLog(@"%@", [o name]); } }
Steve Jobs
第二种:
- (id)valueForUndefinedKey:(NSString *)key第三种:
static char const * const ObjectTagKey; @implementation NSObject (ExampleCategoryWithProperty) @dynamic objectTag; - (id)objectTag { return objc_getAssociatedObject(self, ObjectTagKey); } - (void)setObjectTag:(id)newObjectTag { objc_setAssociatedObject(self, ObjectTagKey, newObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC); }
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