Question

我想创建一个简单的函数来完成从核心数据中获取数据的大量工作

目前

    NSArray * FetchResult = [self fetchEntities: entityForName sortKey: sortKey PredicateString:PredicateString];

我收到编译器警告说

-   (NSArray *)fetchEntities: (NSString *) entityForName sortKey: (NSString *) sortKey PredicateString: (NSString *)PredicateString is not found.

但是谁在乎呢？我知道我应该调用[self class] fetchEntities而不是[self fetchEntities ...]但它是一个类函数。自我已经提到了课程。那有什么问题？

+(NSManagedObject *)FirstfetchEntity: (NSString *) entityForName sortKey: (NSString *) sortKey PredicateString: (NSString *)PredicateString
{
    NSArray * FetchResult = [self fetchEntities: entityForName sortKey: sortKey PredicateString:PredicateString];

    if ([FetchResult count]==0)
    {
        return nil;
    }
    else
    {
        return [FetchResult objectAtIndex:0]; //return the First
    }
}

+(NSArray *)fetchEntities: (NSString *) entityForName sortKey: (NSString *) sortKey PredicateString: (NSString *)PredicateString
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];


    NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init]autorelease];
    NSEntityDescription *entity = [NSEntityDescription entityForName:entityForName inManagedObjectContext:[self managedObjectContext]];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sortDescriptor = [[[NSSortDescriptor alloc] initWithKey:sortKey ascending:NO]autorelease];
    NSArray *sortDescriptors = [[[NSArray alloc] initWithObjects:sortDescriptor, nil]autorelease];
    [fetchRequest setSortDescriptors:sortDescriptors];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:PredicateString];
    [fetchRequest setPredicate:predicate];

    NSError *error = nil;
    NSArray *fetchedObjects = [[self managedObjectContext] executeFetchRequest:fetchRequest error:&error];
    if (fetchedObjects == nil) {
        // Handle the error
    }

    return fetchedObjects;
    [pool release];
}

Answer 1

问题很简单，在编译第一个方法时，编译器不知道第二个方法。您应该在调用之前定义第二个方法，如果方法不会公开使用，可能使用私有接口。

如果您要将方法设为私有方式，请在类实现之前加上类似的内容：

@interface <MyClassName> ()
   + (NSArray *)fetchEntities: (NSString *) entityForName sortKey: (NSString *) sortKey PredicateString: (NSString *)PredicateString;
@end

班级功能中的自我参考班级权利？

1 个答案: