How to get the filename from a given UIImage object?
No you can't, since you can construct a UIImage from pure data without a file.
UIImage does not store the file name it was loaded from. You need to save it separately somewhere on download for future usage.
Related
I need to save an image picked by an image picker on disk and than associate it to a managed object.
I want to store the image path in the managed object (imagePath attribute is nsstring) but I don't know how to call the image because it must be always available until user delete the managed object.
I thought to call every image with managed object's ID but I believe that it is too long and it's still temporary when I try to save my image...
How can I call every image for each managed object?
Thank you!
If you are going to store it on disk why not just store it in core data using the Transformable type.
You can shorten the managed object id using something like:
NSString *_id=[[self.objectID URIRepresentation] lastPathComponent];
Using the managed object's ID turned into a file name string is actually ideal since it is guaranteed to be unique. The length of the name is hardly an issue to the file system.
I'm creating an UIImage like this:
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
Am I responsible for releasing this?
No.
Return Value
An autoreleased image
object containing the contents of the
current bitmap graphics context.
(doc link)
Read the documentation here. As it's written there, it returns an autoreleased object. You don't have to release it. If you want to keep it, you need to retain it somehow.
Just a guess: I make an attribute and make it's type "binary". But in the end, how would I use that? I guess there is an NSData behind the scenes? So that attribute actually takes an NSData?
This question has been asked a number of times and the answer is a bit more complex.
When it comes to binary data you should determine how to store it based on the expected size of data you are going to be working with. The rule is:
Less than 100K;store as a binary property in your main table
Less than 1M; store as a binary property in a ancillary table to avoid over fetching
Greater than 1M; store on disk and store its file path in the Core Data table.
In addition, when you are storing images, it is recommended to store them in a standard format such as JPG or PNG. By using the transformable property type you can actually have your subclass give the appearance of accessing the UIImage class when the actual store is a PNG representation. I go into this in detail in the bog post on Cocoa Is My Girlfriend.
Update
The reason behind storing > 1M binary data on disk is because of the cache. The NSPersistentStoreCoordinator will keep a cache of data so that when your app asks for the "next" object it doesn't need to go back out to disk. This cache works really well. However it is small, very small on iOS. If you pull in a big piece of binary data you can easily blow out that entire cache and your entire app suffers greatly.
That's correct, use binary which is represented as a NSdata object, then u can use uiimages imageWithData class method in order to retrieve your images.
Marcus's answer works, but it's not the easy way - and, AFAICT, it's not how Apple "intends" you to do it. In theory, you should be able to just mark the image as "Transformable", and CD would do everything automatically.
That doesn't work because UIImage is "missing" the implementation of NSCoding - Apple's serialization system - and so the default transformer from CD has no idea how to save an image.
The alternative, which requires a little code, but is still simpler than Marcus's approach ... allegedly you run into Apple's bugs. Apple's CoreData implementation (allegedly) has been broken since 2008 - the custom transformers are ignored for any data-store of type "Binary".
Going back to "CD would do everything automatically, if only UIImage were setup right" ... IMHO, UIImage ought to be serializable, even if the "Default" serialization isn't ideal for all cases. If you fix that, then lo and behold ... CoreData starts saving/laoding UIImage instances with zero coding from you.
Here's code to make your UIImage instances all serializable. All you have to do is import this category / copy paste this category into the classes where you want the "upgraded" UIImage version.
#implementation UIImage (MyCategory)
- (void)encodeWithCoder:(NSCoder *)encoder
{
[encoder encodeDataObject:UIImagePNGRepresentation(self)];
}
- (id)initWithCoder:(NSCoder *)decoder
{
NSData *data = [[decoder decodeDataObject] retain];
return [[UIImage alloc] initWithData:data];
}
#end
My app involves a user being able to drag specific items such as volume sliders and UIImage views. My goal is to be able to save the locations of the items so that the user can not have to drag the items again after re-launch. Unfortunately, I have seen errors along taking the 'saving CGRect rect = item.frame to NSuserDefaultsorNSKeyedArchiver' route. Any other suggestions?
You could use NSStringFromgCGRect() and CGRectFromString() to store them.
If you're using keyed archiving on iPhone, UIKit specifically supports an addition that looks like this: -encodeCGRect:forKey: and does precisely what you want. See the Apple docs for NSCoder's UIKit additions.
If you're using NSUserDefaults, you don't get the luxury of using an explicit encoder for CGRects, but as some other answers say, you could save them as strings using NSStringFromCGRect() and its reverse.
You would probably encode CGRect using NSData and then store NSData object using NSUserDefaults or NSKeyedArchiver.
I'm not sure what errors exactly are you referring in your question, maybe more explanation needed?
You have to convert the floats in the CGRect to NSNumbers and then put them in a Dictionary.
If you need to store a lot of CGRects, I recommend creating a little lightweight class with the CGRect elements as archivable NSNumber attributes. Create an initializer that takes a CGRect. Then write quick NSCoder protocol methods so the entire object can be archived
That way you can you quickly and easy convert, store and then retrieve the CGRects.
Some kind of serialization available in iPhone OS? Is that practically possible or should I quickly forget about that?
I am making a tiny app that stores some inputs in an NSMutableArray. When the user leaves, the inputs should stay alive until he/she returns to continue adding or removing stuff to/from that array.
When the app quits, there must be some way to store all the stuff in the array in a file. Or must I iterate over it, rip everything out and write it i.e. comma-separated somewhere, then the next time go in again, read the stuff in, and iterate over the lines in the file to make an array with that data? That would be hard like a brick. How to?
The easy way, since you already have an NSArray object is to write the array to disk using
- (BOOL)writeToFile:(NSString *)path atomically:(BOOL)flag
and read it back in with:
- (id)initWithContentsOfFile:(NSString *)aPath
or
+ (id)arrayWithContentsOfFile:(NSString *)aPath
You can also use NSCoder.
You can probably search sof for the right code.
So long as the objects in the array implement NSCoding (NSString and NSValue do; if you're storing your own objects it's relatively straightforward), you can use:
[NSKeyedArchiver archiveRootObject: array toFile: filePath];
to save and:
array = [NSKeyedUnarchiver unarchiveObjectWithFile: filePath];
to load.
You can similarly load/save to NSData.
The iPhone SDK is designed to store data using SQLite tables.
You can use NSPropertyListSeralization, since NSArray is a type of property list. You can find more information here.