passing __block parameters to class method (for get request)
我想创建以下类方法:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | +(void) getValue4Key:(NSString*)p_key andSet:(id)p_variable { NSString *baseURLString = <<myURL>>; @try{ AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager]; [manager GET:baseURLString parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) { NSDictionary* element = responseObject[0]; element = [element objectForKey:@"fields"]; p_variable = [element objectForKey:@"value"]; } failure:^(AFHTTPRequestOperation *operation, NSError *error) { NSLog(@"getSystemVariableKey error: %@",error); }]; } @catch (NSException *exception) { NSLog(@"exception %@", exception); } } |
两个问题:
__block类型说明符)如何将块设置为方法参数?
我不认为通过引用传递ivar的方法在以后的某个时间异步设置是一种很好的方法。如果在请求完成之前销毁了对象(在问题#2中称为
相反,您应该使用调用程序可用于设置ivar的完成块来处理此问题:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | + (void)getValue4Key:(NSString*)p_key withCompletion:(void (^)(id value))completion { NSString *baseURLString = <<myURL>>; @try{ AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager]; [manager GET:baseURLString parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) { NSDictionary* element = responseObject[0]; element = [element objectForKey:@"fields"]; id value = [element objectForKey:@"value"]; if (completion) { completion(value); } } failure:^(AFHTTPRequestOperation *operation, NSError *error) { NSLog(@"getSystemVariableKey error: %@",error); if (completion) { completion(nil); } }]; } @catch (NSException *exception) { NSLog(@"exception %@", exception); } } |
然后你会像这样调用这个函数:
1 2 3 4 | YourObject *__weak weakSelf = self; [YourObject getValue4Key:@"your_key" completion:^(id value){ weakSelf.setMe = value; }]; |
现在,如果
这有一个额外的好处,就是不需要通过引用传递ivar指针,你会注意到,在iOS框架中根本不会发生这种情况(