使用NSPredicate的方法减少代码重复

Question

我有这两个类方法，每个方法都带有它的谓词。它们的功能是保存将在mapKit和UITable View中显示的信息。但我看到重复的代码，除了谓词;我的问题是：我怎样才能避免这些重复？

+ (NSArray*)spotType:(NSString*)type{
    NSPersistentContainer *persistenceContainer = [AppDelegate sharedDelegate].persistentContainer;
    NSPredicate* predicate = [NSPredicate predicateWithFormat:@"type =%@", type];
    NSManagedObjectContext *context = persistenceContainer.viewContext;
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Spot"];
    [request setPredicate:predicate];
    NSError *error;
    NSArray *result = [context executeFetchRequest:request error:&error];
    if (error != nil) {
        NSLog(@"[Spot spotType] -> %@", [error localizedDescription]);
        return nil;
    }
    return result;
}

+ (NSArray*)spotWithType:(NSString*)type{
    NSPersistentContainer *persistenceContainer = [AppDelegate sharedDelegate].persistentContainer;
    NSPredicate* predicate = [NSPredicate predicateWithFormat:@"NOT (type = %@)", type];
    NSManagedObjectContext *context = persistenceContainer.viewContext;
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Spot"];
    [request setPredicate:predicate];
    NSError *error;
    NSArray *result = [context executeFetchRequest:request error:&error];
    if (error != nil) {
        NSLog(@"[Spot spotWithType] -> %@", [error localizedDescription]);
        return nil;
    }
    return result;
}

Answer 1

减少代码重复的最基本方法是将公共代码放入共享私有方法中：

- (NSArray*)getSpotType:(NSString*)type withPredicate:(NSString*) pred andMessage:(NSString*)message {
    NSPersistentContainer *persistenceContainer = [AppDelegate sharedDelegate].persistentContainer;
    NSPredicate* predicate = [NSPredicate predicateWithFormat:pred, type];
    NSManagedObjectContext *context = persistenceContainer.viewContext;
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Spot"];
    [request setPredicate:predicate];
    NSError *error;
    NSArray *result = [context executeFetchRequest:request error:&error];
    if (error != nil) {
        NSLog(message, [error localizedDescription]);
        return nil;
    }
    return result;
}
- (NSArray*)spotType:(NSString*)type {
    return [MyClass getSpotType:type withPredicate:@"type =%@" andMessage:@"[Spot spotType] -> %@"];
}
- (NSArray*)spotWithType:(NSString*)type {
    return [MyClass getSpotType:type withPredicate:@"NOT (type = %@)" andMessage:@"[Spot spotWithType] -> %@"];
}