Question

如果我在添加对象时保存在循环外部，而不是在循环中执行此操作，是否会丢失数据？要求外面保存要快得多。

外圈：

for(NSMutableDictionary *result in data){
            [manager newManagedCaf];
            for (NSString *name in result){
                if ([name isEqualToString:@"contact"]){
                NSNumber *num = [NSNumber numberWithInteger:[[result valueForKey:name] integerValue]];
                    [[manager cafCards] setValue:num forKey:name];
                }
                else{
                    [[manager cafCards] setValue:[result valueForKey:name] forKey:name];
                }
            }
            [[manager cafCards] setValue:[NSNumber numberWithBool:YES] forKey:@"synced"];
            }
        }
    if(![[manager cafCards].managedObjectContext save:&error]){
        NSLog(@"Unable to save managed object context.");
        NSLog(@"%@, %@", error, error.localizedDescription);
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"Error: %@", [error localizedDescription]] message:@"Database not working, try again later or inform IT." delegate:self cancelButtonTitle:@"Back" otherButtonTitles:nil, nil];
        [alert show];
        [self getImages:0 con:con withManager:manager];
   }

内圈：

 for(NSMutableDictionary *result in data){
                [manager newManagedCaf];
                for (NSString *name in result){
                    if ([name isEqualToString:@"contact"]){
                    NSNumber *num = [NSNumber numberWithInteger:[[result valueForKey:name] integerValue]];
                        [[manager cafCards] setValue:num forKey:name];
                    }
                    else{
                        [[manager cafCards] setValue:[result valueForKey:name] forKey:name];
                    }
                }

                [[manager cafCards] setValue:[NSNumber numberWithBool:YES] forKey:@"synced"];
                if(![[manager cafCards].managedObjectContext save:&error]){
                    NSLog(@"Unable to save managed object context.");
                    NSLog(@"%@, %@", error, error.localizedDescription);
                    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"Error: %@", [error localizedDescription]] message:@"Database not working, try again later or inform IT." delegate:self cancelButtonTitle:@"Back" otherButtonTitles:nil, nil];
                    [alert show];
                }
            }

当我把错误处理放在外面时，

得到以下错误：

[2664:3215894] Unable to save managed object context.
    2017-06-07 14:48:22.644 [2664:3215894] (null), (null)
    2017-06-07 14:48:22.778 [2664:3215894] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.

Answer 1

没有数据丢失。

这甚至是批处理操作后提交数据（一次）的推荐方法。

但是你也应该在保存行之后移出显示Unable to save...的错误处理。（顺便说一句：UIAlertView已被弃用了很长时间。）

NSObject - 保存循环与外部循环

1 个答案: