Question

我正在尝试将视频的网址保存到核心数据。为此，我创建一个包含URL的字符串，将其保存到核心数据，然后在另一个视图控制器中检索它。在其他View Controller中检索它时，我收到此错误：Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSURL initWithString:relativeToURL:]: nil string parameter'我已经知道保存的URL包含URL，但在接收时，它是nill。我该如何解决这个问题。

以下是保存网址的代码：

- (void) saveVideo {

    NSManagedObjectContext *context = [self managedObjectContext];

    TimeTravelDetails *timeTravelDetails = [NSEntityDescription insertNewObjectForEntityForName:@"TimeTravelDetails" inManagedObjectContext:context];

    NSString *stringForSave = [self.videoURL absoluteString];
    NSLog(@"String being saved: %@", stringForSave);

    [timeTravelDetails setValue: stringForSave forKey:@"urlString"];

    NSError *error = nil;

    if (![self.managedObjectContext save:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    } else {
        NSLog(@"URL String saved");
        NSLog(@"String being saved: %@", stringForSave);
    }

    //NSLog(@"%@", self.videoURL);

}

以下是我检索它：

- (void) getUrl {

    NSManagedObjectContext *context = [self managedObjectContext];

    TimeTravelDetails *timeTravelDetails = [NSEntityDescription insertNewObjectForEntityForName:@"TimeTravelDetails" inManagedObjectContext:context];

    NSString *stringForURL = [[NSString alloc] init];
    stringForURL = timeTravelDetails.urlString;
    NSLog(@"The string has been recieved: %@", stringForURL);
    self.finalURL = [[NSURL alloc] initWithString:stringForURL];

}

Answer 1

在getUrl函数中，您再次创建一个新的核心数据对象（将新的obj插入数据库），而不是查询已保存的数据。像下面这样的sg应该可以用于查询db：

 NSManagedObjectContext *moc = [self managedObjectContext];
 NSEntityDescription *entityDescription = [NSEntityDescription
                                              entityForName:@"TimeTravelDetails" inManagedObjectContext:moc];
 NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entityDescription];

 NSError* error;
 NSArray *saved_time_travel_details = [moc executeFetchRequest:request error:&error];

保存和接收URL无效

1 个答案: