Question

ios 怎么动态向已有类添加属性

Answer 1

在ios运行过程中，有几种方式能够动态的添加属性。
1-通过runtime动态关联对象
主要用到了objc_setAssociatedObject，objc_getAssociatedObject以及objc_removeAssociatedObjects
//在目标target上添加关联对象，属性名propertyname(也能用来添加block)，值value
+ (void)addAssociatedWithtarget:(id)target withPropertyName:(NSString *)propertyName withValue:(id)value {
id property = objc_getAssociatedObject(target, &propertyName);
if(property == nil)
{
property = value;
objc_setAssociatedObject(target, &propertyName, property, OBJC_ASSOCIATION_RETAIN);
}
}
//获取目标target的指定关联对象值
+ (id)getAssociatedValueWithTarget:(id)target withPropertyName:(NSString *)propertyName {
id property = objc_getAssociatedObject(target, &propertyName);
return property;
}
优点：这种方式能够使我们快速的在一个已有的class内部添加一个动态属性或block块。
缺点：不能像遍历属性一样的遍历我们所有关联对象，且不能移除制定的关联对象，只能通过removeAssociatedObjects方法移除所有关联对象。
2-通过runtime动态添加Ivar
主要用到objc_allocateClassPair，class_addIvar，objc_registerClassPair
//在目标target上添加属性(已经存在的类不支持，可跳进去看注释)，属性名propertyname，值value
+ (void)addIvarWithtarget:(id)target withPropertyName:(NSString *)propertyName withValue:(id)value {
if (class_addIvar([target class], [propertyName UTF8String], sizeof(id), log2(sizeof(id)), "@")) {
YYLog(@"创建属性Ivar成功");
}
}
//获取目标target的指定属性值
+ (id)getIvarValueWithTarget:(id)target withPropertyName:(NSString *)propertyName {
Ivar ivar = class_getInstanceVariable([target class], [propertyName UTF8String]);
if (ivar) {
id value = object_getIvar(target, ivar);
return value;
} else {
return nil;
}
}
优点：动态添加Ivar我们能够通过遍历Ivar得到我们所添加的属性。
缺点：不能在已存在的class中添加Ivar，所有说必须通过objc_allocateClassPair动态创建一个class，才能调用class_addIvar创建Ivar，最后通过objc_registerClassPair注册class。
3-通过runtime动态添加property
主要用到class_addProperty，class_addMethod，class_replaceProperty，class_getInstanceVariable
//在目标target上添加属性，属性名propertyname，值value
+ (void)addPropertyWithtarget:(id)target withPropertyName:(NSString *)propertyName withValue:(id)value {
//先判断有没有这个属性，没有就添加，有就直接赋值
Ivar ivar = class_getInstanceVariable([target class], [[NSString stringWithFormat:@"_%@", propertyName] UTF8String]);
if (ivar) {
return;
}
/*
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);
*/
//objc_property_attribute_t所代表的意思可以调用getPropertyNameList打印，大概就能猜出
objc_property_attribute_t type = { "T", [[NSString stringWithFormat:@"@\"%@\"",NSStringFromClass([value class])] UTF8String] };
objc_property_attribute_t ownership = { "&", "N" };
objc_property_attribute_t backingivar = { "V", [[NSString stringWithFormat:@"_%@", propertyName] UTF8String] };
objc_property_attribute_t attrs[] = { type, ownership, backingivar };
if (class_addProperty([target class], [propertyName UTF8String], attrs, 3)) {
//添加get和set方法
class_addMethod([target class], NSSelectorFromString(propertyName), (IMP)getter, "@@:");
class_addMethod([target class], NSSelectorFromString([NSString stringWithFormat:@"set%@:",[propertyName capitalizedString]]), (IMP)setter, "v@:@");
//赋值
[target setValue:value forKey:propertyName];
NSLog(@"%@", [target valueForKey:propertyName]);
YYLog(@"创建属性Property成功");
} else {
class_replaceProperty([target class], [propertyName UTF8String], attrs, 3);
//添加get和set方法
class_addMethod([target class], NSSelectorFromString(propertyName), (IMP)getter, "@@:");
class_addMethod([target class], NSSelectorFromString([NSString stringWithFormat:@"set%@:",[propertyName capitalizedString]]), (IMP)setter, "v@:@");

//赋值
[target setValue:value forKey:propertyName];
}
}
id getter(id self1, SEL _cmd1) {
NSString *key = NSStringFromSelector(_cmd1);
Ivar ivar = class_getInstanceVariable([self1 class], "_dictCustomerProperty"); //basicsViewController里面有个_dictCustomerProperty属性
NSMutableDictionary *dictCustomerProperty = object_getIvar(self1, ivar);
return [dictCustomerProperty objectForKey:key];
}
void setter(id self1, SEL _cmd1, id newValue) {
//移除set
NSString *key = [NSStringFromSelector(_cmd1) stringByReplacingCharactersInRange:NSMakeRange(0, 3) withString:@""];
//首字母小写
NSString *head = [key substringWithRange:NSMakeRange(0, 1)];
head = [head lowercaseString];
key = [key stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:head];
//移除后缀 ":"
key = [key stringByReplacingCharactersInRange:NSMakeRange(key.length - 1, 1) withString:@""];
Ivar ivar = class_getInstanceVariable([self1 class], "_dictCustomerProperty"); //basicsViewController里面有个_dictCustomerProperty属性
NSMutableDictionary *dictCustomerProperty = object_getIvar(self1, ivar);
if (!dictCustomerProperty) {
dictCustomerProperty = [NSMutableDictionary dictionary];
object_setIvar(self1, ivar, dictCustomerProperty);
}
[dictCustomerProperty setObject:newValue forKey:key];
}
+ (id)getPropertyValueWithTarget:(id)target withPropertyName:(NSString *)propertyName {
//先判断有没有这个属性，没有就添加，有就直接赋值
Ivar ivar = class_getInstanceVariable([target class], [[NSString stringWithFormat:@"_%@", propertyName] UTF8String]);
if (ivar) {
return object_getIvar(target, ivar);
}
ivar = class_getInstanceVariable([target class], "_dictCustomerProperty"); //basicsViewController里面有个_dictCustomerProperty属性
NSMutableDictionary *dict = object_getIvar(target, ivar);
if (dict && [dict objectForKey:propertyName]) {
return [dict objectForKey:propertyName];
} else {
return nil;
}
}
优点：这种方法能够在已有的类中添加property，且能够遍历到动态添加的属性。
缺点：比较麻烦，getter和setter需要自己写，且值也需要自己存储，如上面的代码，我是把setter中的值存储到了_dictCustomerProperty里面，在getter中再从_dictCustomerProperty读出值。

4-通过setValue:forUndefinedKey动态添加键值
这种方法优点类似property，需要重写setValue:forUndefinedKey和valueForUndefinedKey:，存值方式也一样，需要借助一个其它对象。由于这种方式没通过runtime，所以也比较容易理解。