同样是之前的存储四个textField的例子

在项目中创建后缀为” .xcdatamodel “的存储文件，在其attribute中创建属性，lineNum和lineText，类型为integer116和String

 

然后直接上代码：

- (void)applicationWillResignActive:(NSNotification *)notification {    //获取appDelegate    BIDAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];    //获取上下文context    NSManagedObjectContext *context = [appDelegate managedObjectContext];        NSError *error;        for (int i = 1; i <= 4; i++) {        NSString *fieldName = [NSString stringWithFormat:@"line%d", i];        UITextField *theField = [self valueForKey:fieldName];        //创建提取请求        NSFetchRequest *request = [[NSFetchRequest alloc] init];        //创建托管对象（Managed Objects）        NSEntityDescription *entityDescription = [NSEntityDescription                                                  entityForName:@"Line"                                                  inManagedObjectContext:context];        //为请求设置Entity，指定希望的对象实体        [request setEntity:entityDescription];                //谓词（predicate）（断言？）类似于SQL中的where语言        //这句的意思是通知提取请求仅搜索lineNum 属性设置为i 的对象        NSPredicate *pred = [NSPredicate                             predicateWithFormat:@"(lineNum = %d)", i];        //设置断言        [request setPredicate:pred];                NSManagedObject *theLine = nil;                //执行提取请求,执行之后，context将跟踪你对该数组（objects）中返回的托管对象（theLine）的任何修改，最终发送sava：时保存        NSArray *objects = [context executeFetchRequest:request                                                  error:&error];                if (objects == nil) {            NSLog(@"There was an error!");            // Do whatever error handling is appropriate        }        if ([objects count] > 0)//原本存在，因为有设置断言，所以这里的count=1            theLine = [objects objectAtIndex:0];        else//初次存储            theLine = [NSEntityDescription                       insertNewObjectForEntityForName:@"Line"                       inManagedObjectContext:context];                [theLine setValue:[NSNumber numberWithInt:i] forKey:@"lineNum"];        [theLine setValue:theField.text forKey:@"lineText"];            }    //保存数据    [context save:&error];}

 

 

viewDidLoad中

- (void)viewDidLoad {
       [super viewDidLoad]; // Do any additional setup after loading the view from its nib.     BIDAppDelegate *appDelegate =     [[UIApplication sharedApplication] delegate];     NSManagedObjectContext *context = [appDelegate managedObjectContext];     NSEntityDescription *entityDescription = [NSEntityDescription                                               entityForName:@"Line"                                               inManagedObjectContext:context];     NSFetchRequest *request = [[NSFetchRequest alloc] init];     [request setEntity:entityDescription];     NSError *error;     NSArray *objects = [context executeFetchRequest:request error:&error]; if (objects == nil) {
           NSLog(@"There was an error!"); // Do whatever error handling is appropriate     } for (NSManagedObject *oneObject in objects) {
           NSNumber *lineNum = [oneObject valueForKey:@"lineNum"];         NSString *lineText = [oneObject valueForKey:@"lineText"];         NSString *fieldName = [NSString                                stringWithFormat:@"line%d", [lineNum integerValue]];         UITextField *theField = [self valueForKey:fieldName];         theField.text = lineText;     }     UIApplication *app = [UIApplication sharedApplication];     [[NSNotificationCenter defaultCenter] addObserver:self         selector:@selector(applicationWillResignActive:)         name:UIApplicationWillResignActiveNotification object:app]; }