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];
}
本文转自老Zhan博客园博客，原文链接：http://www.cnblogs.com/mybkn/archive/2012/03/31/2427157.html，如需转载请自行联系原作者
