I have set up a sharedCache using ASIHttprequest and it is created from the xml I parse in my subview. I was woundering if I can then access that sharedCache from my mainview to do a few things things that will speed my tables up?
any idea, suggestions, thoughts of examples would be greatly appreciated.
There's already a sharedCache provided by ASIDownloadCache. It's visible anywhere in your application (assuming you #import "ASIDownloadCache.h"), so you should be able to call [ASIDownloadCache sharedCache] and use it.
EDIT: To use several caches is not too tricky. Create a separate class which is included by both your main view and your subview. In there, define a method to return one or more ASIDownloadCache objects, and provide an implementation, similar to this:
DownloadCaches.h
#import "ASIDownloadCache.h"
#interface DownloadCaches : NSObject
+ (ASIDownloadCache *)imageCache;
#end
DownloadCaches.m
#import "DownloadCaches.h"
#implementation DownloadCaches
static ASIDownloadCache *imageCache = nil;
+ (ASIDownloadCache *)imageCache
{
if(imageCache == nil)
{
imageCache = [[ASIDownloadCache alloc] init];
// set imageCache-specific options here
}
return imageCache;
}
#end
You only ever need to call [DownloadCaches imageCache] and it will be initialised if not already, and then returned to you.
Related
I got a question about subclassing.
I start with my first view:
in my .h file:
#interface viewAController : UIViewController
in my .m file:
-(void)viewDidLoad
{
[super viewDidLoad];
NSLog(#"Begin view");
udpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_main_queue()];
NSError *error = nil;
if (![udpSocket bindToPort:12345 error:&error]) //check ff of dit werkt!
{
NSLog(#"F you");
return;
}
NSLog(#"Derde line");
if (![udpSocket beginReceiving:&error])
{
NSLog(#"Screw you!");
return;
}
}
Porting and beginreceiving goes well.
and then when I subclass viewAController:
#interface viewBController : viewAController
in my .m file:
-(void)viewDidLoad{
[super viewDidLoad];
}
I am expecting that my subclass [viewBController], will display all of the NSLogs, because Im calling the super viewDidLoad.
Instead it is saying: F you!
Oke I understand that I can only bind once to the port, BUT Im expecting an error message, this does not show.
So I delete the binding and then I get Screw you, apparently I cannot say beginreceiving when Im not binding to a port. Without these two methods it works just fine though, it is printing everything out of the parent.
QUESTIONS:
Should I bind? I actually only need to listen to port 12345, should I just implement this differently?
Should I work without bind and without beginreceiving? I think I prefer with binding so that I wont listen to all of my ports.
Why cant I do beginreceiving when I dont bind?
How can I show the error?? Cause it is not printing any errors ...
greetz
What you are doing is right.But i have only one question to ask whether you have added the object of derived ViewController to some View.
Unless you wont add it you wont get the didLoad Of your superclass get fired.
Check by adding the object of your derived View to SomeView.
This is wrong you are doing
NSLog("#Hi there!");
you have to use
NSLog(#"Hi there!");
And if this is a typo (I hope it is) you have to add your sub class to some where using add subview or pushing it.
I am stuck on what is supposed to be a very simple thing to do: have a Core Data Entity store / display (through bindings) an image assigned as a transformable attribute.
I've read many related posts on the Stack (e.g., see here and here), but am still having trouble with it, after having developed sample code and researched other articles (e.g., see here as well as here). This is related to my earlier question, which I still have not resolved.
I created a simple doc-based Core Data App to demonstrate the problem. The Core Data managed object is called "TheEntity" and the attribute "theImageAtt." The entity as defined in Core Data is shown below (ImageValueTransformer is the NSValueTransformer):
I let XCode generate the NSManagedObject subclass header and implementation files (I left out the code for the "name" attribute to make it simpler):
// TheEntity.h
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
#import "ImageValueTransformer.h"
#interface TheEntity : NSManagedObject
#property (nonatomic, retain) NSImage * theImageAtt;
#end
-----------------------
// TheEntity.m
#import "TheEntity.h"
#implementation TheEntity
#dynamic theImageAtt;
#end
Below are the header and implementation files for my "ImageValueTransformer." Lots of examples of this on the Stack and elsewhere (the tiff rep is arbitrary).
// ImageValueTransformer.h
#import <Foundation/Foundation.h>
#interface ImageValueTransformer : NSValueTransformer
#end
-------------------------------
// ImageValueTransformer.m
#import "ImageValueTransformer.h"
#implementation ImageValueTransformer
+ (BOOL)allowsReverseTransformation {return YES;}
+ (Class)transformedValueClass {
return [NSData class]; // have also tried: return [NSImage class];
}
- (id)transformedValue:(id)value {
NSData *data = [value TIFFRepresentation];
return data;
}
- (id)reverseTransformedValue:(id)value {
NSImage *imageRep = [[NSImage alloc] initWithData:value];
return imageRep;
}
#end
The Value Transformer can be initialized / registered by allocating an instance of it in MyDocument.m, but in the end, it doesn't matter that much as long as the transformer header is imported into the theEntity Header (see above). I have experimented with this and it does not remove the error I get below. For reference, there is earlier discussion on whether or not the value transformer needs to be registered (see the comments by CornPuff and Brian Webster).
Back to the problem at hand, a good code example from Apple is here which shows an alternative initialization of the value transformer, I tried that setup too.
Putting this into action, I have a method to load a test image and assign it to the transformable attribute in MyDocument.m (from a selected Entity instance in an NSTable):
- (IBAction)addImg:(id)sender {
NSImage *theImg = [[NSImage alloc] initWithContentsOfFile:#"/Desktop/testImage.jpg"];
//[theImageView setImage:theImg]; // as a test, this displays ok
// "theEntities" below are defined as an IBOutlet to my Array Controller:
[theEntities setValue:theImg forKeyPath:#"selection.theImageAtt"];
NSLog(#"after setting the image ..."); // this never logs
}
Zeroing-in on where the code breaks, the line below:
[theEntities setValue:theImg forKeyPath:#"selection.theImageAtt"];
gives the error:
Cannot create BOOL from object <4d4d002a 0003717e 8989898a 8a8a8b8b 8b8b8b8b
8a8a8a89 89898888 88878787 8a8a8a89 89898888 88888888 88888889 89898a8a
8a8a8a8a 8b8b8b88 88888787 87898989 8a8a8a89 89898a8a 8a8c8c8c 8b8b8b8a
8a8a8888 .... and so on for the size of the Image array ...
If I comment out the said line above then my NSTable populates just fine (so the bindings and array controller seem ok), but of course with no image in the NSImageView.
As a check, the conversion code used in the Image Transformer works as expected (this is tested separately from the value transformer):
// Image to Data Conversion:
NSImage *imageIn = [[NSImage alloc] initWithContentsOfFile:#"testImage.jpg"];
NSData *imgData = [imageIn TIFFRepresentation];
NSImage *imageOut = [[NSImage alloc] initWithData:imgData];
[theImageDisplay setImage:imageOut];
What am I missing on this?
I found that the error reported above, namely,
Cannot create BOOL from object ...
does not occur when using an Image Well or Image Cell (subclasses of NSImageView) rather than the Custom View that I was trying to write to earlier.
So for now I'm using the default value transformer rather than a custom value transformer. This is a workable solution, but academically speaking, it would be nice to know why the default Custom View led to errors when binding to a Core Data attribute (defined as transformable in the Core Date Model).
Digging into this a little further, the Image Well inherits from NSImageView, so at least one difference is that they are distinct with regard to the "editable" property (Image Wells are editable which plays well with Drag-n-Drop). So in an attempt to reconcile these two, I set my Custom View to editable, thinking that this might resolve the problem:
theImageView = [[NSImageView alloc] init];
[theImageView setEditable:YES];
But it must be something else, this does not resolve the error above. For now at least, I have a workable solution. Should others encounter this, I hope these notes are helpful!
I want to have an static UIImage so I could access it from different classes. I've tried this way, but didn't worked:
Made Constans.h file with:
static UIImage *myImage;
And after that I import this header where it's needed. I thought that at this moment myImage was static and any changes made on this object would be visible everywhere. But it looks like every class is working on it's own myImage instance. Is there any way to have such static UIImage?
Edit:
Property in AppDelegate works fine. I have now static UIImage, but still I don't have effect I was expecting.
I have an UIImageView in ViewController. I load an image to my delegate.myImage and after I do:
delegate.myImage = [UIImage imageNamed:#"blah.png"];
myImageView.image = delegate.myImage;
Image is loaded, but after I want to change it in AppDelegate, but when I change myImage this way:
delegate.myImage = [UIImage imageNamed:#"blah2.png"];
nothing change in myImageView. It's like myImageView.image = delegate.myImage copied memory address of myImage so after if I change reference of myImage it's not affecting myImageView.image. I wanted to have an UIImage that after any changes it would also affect myImageView.
Is there other way than having an reference to myImageView in AppDelegate?
Rather than making an explicitly application-wide image, just use [UIImage imageNamed:]. This handles caching of the image for you! Whereever you need to use the image, just access it like so:
[UIImage imageNamed:#"imageName.png"]
Note: this will cause there to be a single copy of the image in memory. You can't unload it -- but newer versions of iOS may unload it behind the scenes upon low memory conditions.
See also the API docs for [UIImage imageNamed:].
Btw, imageNamed is often used for small images that get used multiple times -- e.g. table cell images -- but there's no reason to not use it on large images if you genuinely want a static app-wide image.
The keyword static makes a variable local to the compilation unit where it id defined. This means you can safely have the same symbol defined in multiple .c files; all those declarations will not collide and each file will have its own private symbol.
Put simply, if you really want to define a global variable that is accessed by any part of your program, you do not need the static keyword. In this case, though, the "trick" is declaring the variable in a header file (that you include everywhere the global should be visible) like this:
extern UIImage *myImage;
and then provide a definition for that variable in one single place (.c file) without the static keyword. The extern keyword tells the compiler that the definition for that symbol is not found inside of the current compilation unit (.c file), but in a different one.
Now, as many others have pointed out, you could better do that by means of a singleton, although it is usually recognized that using a singleton to mask a global variable is usually a way to mask a design problem.
That's a C problem (not specifically related to Objective-C or iOS)
The static keyword make the variable sticky inside its compilation unit.
When you #include (or #import in ObjC) a header, that's like if its content were copied & pasted into the file that includes it. As a reminder, ".h" files are not compiled (they are just included in ".m" files that themselves compile)
So that works exactly the same way as if you were typing the same lines of code you have in your .h in any file that #include it.
This explains why in each of your source files that #include "Constants.h" they each see a different instance of the myImage variable.
Instead you should:
Use the Singleton Pattern, that is specifically made for such cases
Or use the static keyword in an implementation file ("Constants.m") to make this variable sticky inside the compilation unit of this "Constants.m" file
I highly recommand to go with the Singleton Pattern for such cases anyway. More info on Singleton Pattern here in the Apple official DevPedia
You can create a #property (nonatomic, retain) UIImage *image; in your app delegate and in every class you want to use the image you can create AppDelegate *delegate=(AppDelegate *)[[UIApplication sharedApplication] delegate]; and then access to the UIImage from the delegate object like this :
[imageView setImage:[delegate image]];
Or you can use a class like this :
header file
#interface Data : NSObject
#property (nonatomic, strong) UIImage *image;
+ (Data *)sharedInstance;
+ (id)allocWithZone:(NSZone*)zone;
- (id)init;
- (id)copyWithZone:(NSZone *)zone;
#end
implementation file
#implementation Data
#synthesize image;
static Data *sharedInstance=nil;
+ (Data *)sharedInstance {
if (sharedInstance == nil) {
sharedInstance = [[super allocWithZone:NULL] init];
}
return sharedInstance;
}
+ (id)allocWithZone:(NSZone*)zone {
return [self sharedInstance];
}
- (id)init
{
self = [super init];
if (self) {
}
return self;
}
- (id)copyWithZone:(NSZone *)zone {
return self;
}
#end
Then, you have to import Data.h in every class you want and then use :
UIImageView *imageView=[[UIImageView alloc] init];
[imageView setImage:[[Data sharedInstance] image]];
This works great for me :)
Use the singleton pattern.
If your code is ARC follow this link http://lukeredpath.co.uk/blog/a-note-on-objective-c-singletons.html
In iPhone the AppDelegate class Acts a Static Class. so you can do the same thing which you have done in Constant.h in the YourAppDelegate Class. But dont use Static Keyword.
I am not very Sure but thinks it will work. :)
You can use UIImage category as example to get this picture.
In your .h file just add your static method.
#import <UIKit/UIKit.h>
#interface UIImage (StaticImage)
+(UIImage *)staticImage;
#end
And in your .m file do following steps:
#import "UIImage+StaticImage.h"
//This is your static image
static UIImage *myStaticImage;
#implementation UIImage (StaticImage)
+(void)initialize{
//Important to add this condition, because this method will be called for every
//child class of UIImage class
if (self == [UIImage class]){
myStaticImage = [[UIImage alloc] init];
}
}
+(UIImage *)staticImage{
//Just return your existing static image
return myStaticImage;
}
#end
I want to make a singleton containing information "title, comments, Two picture" and it saves all the information in an array
I want to do is these objects in my application I use it All The Time
#interface CarteManager : NSObject {
NSMutableArray *carteMan ;
}
#property(nonatomic,retain) NSMutableArray *carteMan;
+(CarteManager*)sharedInstance;
-(void)ajouttitre:(NSString*)txt;
-(void)ajoutcom:(NSString*)com;
-(void)ajoutimage1:(UIImage*)img;
-(void)ajoutimage2:(UIImage*)img;
#end
In order to create a Singleton you will need a static instance.
#implementation CarteManager
static CarteManager *_carteManager = nil;
+(CarteManager*)sharedInstance {
if (!_carteManager) {
_carteManager = [[CarteManager alloc] init];
}
return _carteManager;
}
// your other codes
#end
And before creating a Singleton, make sure that you really need a Singleton. Please pay special attention to Singleton: How should it be used.
You didn't state your problem. If it's how to make the object a singleton, you can find several possible implementations in the question What does your Objective-C singleton look like?.
Here is a simple one for you guys . I'm defining a class to store variables in so I can reuse those variables in different ViewControllers .
Here is how I do it, it`s obviously not working ( that's why I'm asking a question ... ):
I declare a class :
VariableStore.h
#interface VariableStore : NSObject {
int evTe;
}
#property (nonatomic) int evTe;
+ (VariableStore *)shareInstance;
#end
VariableStore.m
#implementation VariableStore
#synthesize evTe;
+ (VariableStore *)sharedInstance {
static VariableStore *myInstance = nil;
return myInstance;
}
#end
Now in my FirstViewController I want to set the value for evTe :
[[VariableStore sharedInstance] setEvte:2];
NSLog(#"value testing, %i", evTe);
And this keeps on returning 0 unfortunately, Im obviously missing something important here but I can't figure out what it is .
Later on Id like to set the value for evTe here in the FirstViewController and then reuse it back in the SecondViewController ..
You are setting your shared instance to nil and then returning it:
static VariableStore *myInstance = nil;
return myInstance;
A nil instance won't hold your variable. It's nil.
First off you shouldn't be using a singleton to pass around variables. If you're going to do that then you might as well just use global variables instead (don't do that either by, the way). Second, if you insist on using a singleton, you need to read up on how to use them.
Finally, if you want to pass variables between view controllers, you either need another view controller that is a parent to the two to facilitate passing data between them, or one needs to call the other and take the first one or its data as a parameter.
Well, you're asking for the value of evTe without calling the object to which it belongs. Try this:
NSLog(#"value testing, %i", [[VariableStore sharedInstance] evTe]);
If you keep using the singleton for a number of times, you might want to do:
VariableStore *vStore = [VariableStore sharedInstance];
so you can do:
[vStore setEvTe:2];
NSLog(#"value testing, %i", [vStore evTe]);
And look out for what Matt said about nilling your singleton ;)
I think in nslog you should output not just evTe, but [[VariableStore sharedInstance] evTe].
First, you have to declare the static variable outside the function, in a way both controllers can access.
static VariableStore* myInstance = nil;
The singleton sharedInstance should be:
if(myInstance == nil)
{
myInstance = [[VariableStore] alloc] init];
}
return myInstance;