在 CoreData 上保存和检索 UIImage [英] Save and Retrieve of an UIImage on CoreData
问题描述
在我的应用程序中，我试图在核心数据中保存和检索图像.我能够在 UIimage 约定到 NSData 之后成功保存图像，但是当我尝试将图像作为 NSData 获取时，它显示如下所示的输出，
In my app, I am trying to save and retrieval of an image in core data. I am able to save an image successfully after convention of UIimage into NSData, But when I am trying to get an image as NSData it shows output as given below,
情况 1:当尝试从 DB 中显示为字符串时.
case 1: When trying to display as a string from DB.
<Event: 0x5b5d610> (entity: Event; id: 0x5b5ce30 <x-coredata://F51BBF1D-6484-4EB6-8583-147E23D9FF7B/Event/p1> ; data: <fault>)
情况 2:当尝试显示为数据时
case 2: When trying to display as Data
[Event length]: unrecognized selector sent to instance 0x5b3a9c0
2010-07-28 19:11:59.610 IMG_REF[10787:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Event length]: unrecognized selector sent to instance 0x5b3a9c0'
我的代码，
to save:
NSManagedObjectContext *context = [self managedObjectContext];
newsObj = [NSEntityDescription insertNewObjectForEntityForName:@"Event" inManagedObjectContext:context];
NSURL *url = [NSURL URLWithString:@"http://www.cimgf.com/images/photo.PNG"];
NSData *data = [[NSData alloc] initWithContentsOfURL:url];
uiImage = [UIImage imageWithData:data];
NSData * imageData = UIImagePNGRepresentation(uiImage);
[newsObj setValue:imageData forKey:@"imgPng"];
NSError *error;
@try{
if (managedObjectContext != nil) {
if (![managedObjectContext save:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
NSString * infoString = [NSString stringWithFormat:@"Please check your connection and try again."];
UIAlertView * infoAlert = [[UIAlertView alloc] initWithTitle:@"Database Connection Error" message:infoString delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[infoAlert show];
[infoAlert release];
}
}
}@catch (NSException *exception) {
NSLog(@"inside exception");
}
检索，
NSManagedObjectContext *context = [self managedObjectContext];
NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity1 = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:context];
[fetchRequest setEntity:entity1];
NSError *error;
NSArray * array = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (array == nil) {
NSLog(@"Testing: No results found");
}else {
NSLog(@"Testing: %d Results found.", [array count]);
}
NSData * dataBytes = [[array objectAtIndex:0] data];
image = [UIImage imageWithData:dataBytes];
[fetchRequest release];
}
@catch (NSException *exception) {
NSLog(@"inside exception");
}
Error:
Testing: 3 Results found.
2010-07-28 23:27:51.343 IMG_REF[11657:207] -[Event data]: unrecognized selector sent to instance 0x5e22ce0
2010-07-28 23:27:51.344 IMG_REF[11657:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Event data]: unrecognized selector sent to instance 0x5e22ce0'
*** Call stack at first throw:
(
0 CoreFoundation 0x02566919 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x026b45de objc_exception_throw + 47
2 CoreFoundation 0x0256842b -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
3 CoreFoundation 0x024d8116 ___forwarding___ + 966
4 CoreFoundation 0x024d7cd2 _CF_forwarding_prep_0 + 50
5 IMG_REF 0x00003b06 -[IMG_REFViewController showAction] + 353
6 UIKit 0x002bae14 -[UIApplication sendAction:to:from:forEvent:] + 119
7 UIKit 0x004c214b -[UIBarButtonItem(UIInternal) _sendAction:withEvent:] + 156
8 UIKit 0x002bae14 -[UIApplication sendAction:to:from:forEvent:] + 119
9 UIKit 0x003446c8 -[UIControl sendAction:to:forEvent:] + 67
10 UIKit 0x00346b4a -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
11 UIKit 0x003456f7 -[UIControl touchesEnded:withEvent:] + 458
12 UIKit 0x002de2ff -[UIWindow _sendTouchesForEvent:] + 567
13 UIKit 0x002c01ec -[UIApplication sendEvent:] + 447
14 UIKit 0x002c4ac4 _UIApplicationHandleEvent + 7495
15 GraphicsServices 0x02dccafa PurpleEventCallback + 1578
16 CoreFoundation 0x02547dc4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
17 CoreFoundation 0x024a8737 __CFRunLoopDoSource1 + 215
18 CoreFoundation 0x024a59c3 __CFRunLoopRun + 979
19 CoreFoundation 0x024a5280 CFRunLoopRunSpecific + 208
20 CoreFoundation 0x024a51a1 CFRunLoopRunInMode + 97
21 GraphicsServices 0x02dcb2c8 GSEventRunModal + 217
22 GraphicsServices 0x02dcb38d GSEventRun + 115
23 UIKit 0x002c8b58 UIApplicationMain + 1160
24 IMG_REF 0x00002aac main + 102
25 IMG_REF 0x00002a3d start + 53
)
terminate called after throwing an instance of 'NSException'
注意:执行 NSData * dataBytes = [[array objectAtIndex:0] data] 时会出现上述错误；线.数据模型 http://www.freeimagehosting.net/uploads/7c286931cc.png
Note: Above error is coming when going to execute NSData * dataBytes = [[array objectAtIndex:0] data]; line. Data Model http://www.freeimagehosting.net/uploads/7c286931cc.png
我花了很多时间在这上面.请帮帮我！
I spent a lot of time with this. Please help me out!
推荐答案
当您检索图像时，您正在执行获取请求并将结果存储在变量 array 中，即 array 保存了一个 NSArray 的 Event 对象.然后，稍后，您分配:
When you retrieve the image, you're performing the fetch request and storing the results in the variable array, meaning array holds an NSArray of Event objects. Then, later, you assign:
dataBytes = [array objectAtIndex:0];这意味着您声明为 NSData 的 dataBytes 现在实际上是 Event 的一个实例.然后当你去初始化图像时， imageWithData: 的部分实现调用 length 上它期望是你的 NSData 对象，但实际上是一个事件对象，因此错误信息.
This means that dataBytes, which you declared as NSData, is now actually an instance of Event. Then when you go to initialize the image, part of the implementation of imageWithData: calls length on what it expects to be your NSData object, but is actually an Event object, hence the error message.
你应该调整你的代码来阅读:
You should adjust your code to read:
dataBytes = [[array objectAtIndex:0] imgPng];这样，您将从数组中取出第一个 Event 对象，然后获取其 imgPng 属性(NSData 的一个实例，这正是您想要的).
That way, you're getting the first Event object out of the array, then fetching its imgPng property (an instance of NSData, which is what you want).
作为旁注，您在上面的行中使用 alloc-init 声明 dataBytes 可能是无关紧要的，因为您更改了 dataBytes 是之后立即来自您的 Event 的数据.
As a side note, your declaration of dataBytes using the alloc-init on the line above may be extraneous, since you change dataBytes to be the data from your Event immediately afterwards.
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