I have a little problem, when I have to access to one class I create a new instance
Class *class = [[Class alloc] init];
the problem is that I don't want to create a new instance but use the current instance, I want only to communicate between two class...how can I pass a value without create a new instance?
You can use a Singleton class to create a shared object that can be accessed for the lifetime of the app, here's a simple (though not 100% foolproof) way to create one:
+ (id) sharedInstance {
static Foo *__sharedInstance;
if (nil == __sharedInstance) {
__sharedInstance = [[Foo alloc] init];
}
return __sharedInstance;
}
More here
If you just want to perform specific operations, or get information from the class, you can use a class method by using "+" instead of "-" in the method name like so:
+ (void) doSomething {
NSLog(#"This class is %#", self);
}
Then you can simply call [Class doSomething] to perform operations without having to create a new instance.
Related
I need to update the value of a NSProgressIndicator through a class different from the one where the outlet was defined.
Es:
In class A.h I define the outlet for the NSProgressIndicator and link it.
In class A.m I have a method to update the doubleValue of the Indicator.
In class B.m I call, through an istance of class A, the method but nothing happens.
Istead if i call the same method within class A it works fine.
What am I missing ?
//REQUESTED CODE:
//Class A (AppDelegate)
A.m
//Other stuff
-(void)update_indicator:(double)value {
//Method that updates the value of the indicator
[progress_indicator setDoubleValue:(double)value];
[progress_indicator setNeedsDisplay:YES];
}
//Class B (Drawing class - subclass of NSView)
B.m
- (void)drawRect:(NSRect)dirtyRect
{
[super drawRect:dirtyRect];
//Create istance;
A *istance = [[A alloc] init]; //Alloc class A and init it
[A update_indicator:50.0];
//Other code..
}
The strange thing is that if I call -(void)update_indicator:(double)value within class A, where the outlet is defined, it works fine, if I call it from B it is being called but the progress bar is not showing.
If A is the delegate class of the application you can get the good instance using this [[NSApplication sharedApplication]delegate], instead of creating a new instance.
Otherwise, you should make class A a singleton.
Take a lock at this example http://www.galloway.me.uk/tutorials/singleton-classes/
I am able to support the Make New command of AppleScript for my app, however the returned 'specified object' (an NSUniqueIDSpecifier) for the core data managed object is useless. The following AppleScript returns the error message:
error "SpellAnalysis got an error: Invalid key form." number -10002 from level id "x-coredata:///Levels/tC5A49E01-1CE1-4ED6-8F6B-BC0AE90E279A2"
tell application "SpellAnalysis"
set thisLevel to make new «class Slev» with properties {«class Saln»:3}
get properties of thisLevel
end tell
So the newly created Levels object can not be acted upon in AppleScript. I've combed the Web for a solution to this and the closest thing I have found is Bill Cheeseman's example app, "WareroomDemo" which specifically deals with Cocoa Scriptability for Core Data apps (the Sketch example does not use Core Data). Unfortunately, it is a dated example, running only on pre-64-bit XCode and I can't actually run it--I can only look at the code. His app's Make Command may have the same limitations for all I know.
The returned 'objectSpecifier' is unable to refer to the created object either as a safe-guard against corrupting Core Data's organizing scheme, or perhaps because the returned object is an un-cashed 'fault'. I think the latter possibility is unlikely because I can force the fault to cash (by getting a property value on the managed object) , yet I get the same error message with the AppleScript.
Here is the method that creates my class:
- (id)newScriptingObjectOfClass:(Class)class forValueForKey:(NSString *)key withContentsValue:(id)contentsValue properties:(NSDictionary *)properties { // Creates a new Lesson object in response to the AppleScript 'make' command.
// Documentation for 'newScriptingObject…' states that to create a new class object when using Core Data, you intercede using the following method (or you can subclass the NSCreateCommand's 'performDefaultImplementation' method and put your NSManagedObject init code there):
if (class == [Levels class]) {
//NSLog(#"class: %#",class);
NSEntityDescription *levelsEntity = [NSEntityDescription
entityForName:#"Levels"
inManagedObjectContext:levelsDBase];
NSManagedObject *levelObject = [[NSManagedObject alloc] initWithEntity:levelsEntity insertIntoManagedObjectContext:levelsDBase];
SLOG(#"lessonObject: %#", lessonObject);
NSString *levelNumberString = [[properties objectForKey:#"levelNumber"] stringValue];
SLOG(#"levelNumberString: %#", levelNumberString);
[levelObject setValue:levelNumberString forKey:#"levelNumber"];
return levelObject; // When using Core Data, it seems that you return the newly created object directly
}
return [super newScriptingObjectOfClass:(Class)class forValueForKey:(NSString *)key withContentsValue:(id)contentsValue properties:(NSDictionary *)properties];
}
Here is my object specifier method:
- (NSScriptObjectSpecifier *)objectSpecifier {
// This NSScriptObjectSpecifiers informal protocol returns a unique ID specifier specifying the absolute string of the URI representation of this managed object. // AppleScript return value: 'level id <id>'.
// The primary container is the application.
NSScriptObjectSpecifier *containerRef = nil; // I understand that if the application is the container, this is value you use for the container reference
NSString *uniqueID = [[[self objectID] URIRepresentation] absoluteString];
return [[[NSUniqueIDSpecifier alloc] initWithContainerClassDescription:[NSScriptClassDescription classDescriptionForClass:[NSApp class]] containerSpecifier:containerRef key:#"levelsArray" uniqueID:uniqueID] autorelease];
}
The problem lies with the specifier method. The Sketch example actually uses the technique that I needed. I overlooked it many times because I didn't see how it would apply to Core Data managed objects. Instead of returning the objects uniqueID, you make it return the managedObject index using the 'indexOfObjectIdenticalTo:' method as follows:
- (NSScriptObjectSpecifier *)objectSpecifier {
NSArray *levelsArray = [[NSApp delegate] levelsArray]; // Access your exposed to-many relationship--a mutable array
unsigned index = [levelsArray indexOfObjectIdenticalTo:self]; // Determin the current objects index
if (index != (unsigned)NSNotFound) {
// The primary container is the document containing this object's managed object context.
NSScriptObjectSpecifier *containerRef = nil; // the appliation
return [[[NSIndexSpecifier allocWithZone:[self zone]] initWithContainerClassDescription:[NSScriptClassDescription classDescriptionForClass:[NSApp class]] containerSpecifier:containerRef key:#"levelsArray" index:index] autorelease];
} else {
return nil;
}
}
Note that this method resides within a subclass of your Core Data managedObject--in this case, the 'Levels' class. The 'self' within the 'indexOfObjectIndenticalToSelf:' method refers to the current managedObject ('Levels') being handled. Also, be sure to provide the specifier (accessor) type to your 'sdef' file, like this:
<element type="level">
<cocoa key="levelsArray"/>
<accessor style="index"/>
</element>
Quick Question:
I am creating an object from the MainWindowController:
about = [[About alloc]init];
In the Class About I do my Init:
-(id)init{
if(!_viewAbout){
[NSBundle loadNibNamed:#"About" owner:self];
[NSApp beginSheet:self.viewAbout modalForWindow:*?????* modalDelegate:self didEndSelector:NULL contextInfo:NULL];
}
return self;
}
My problem is that the Window is created in the MainWindowController. My question is how to call/send a message to the creator of the class if the class itself doesn't know the master class?
If I understand you correctly, most classes have self.superclass and just super, like
[super someMethod....
or
[self.superclass blegh....
Or are you asking for the class that creates another class ? If that is the case, you need to declare the creator class inside the other one, some (id) variable would do the trick.
But the most popular design pattern on the mac is the delegate pattern, and once you start using that you will love it. Declaring a delegate is usually the way Cocoa and UIKit do things, but other programming languages might not. Obj-C doesn't have any magic variables like python f.ex. has. Either you have a delegate or you have a declared variable which you would set right after the init/alloc stuff.
Also your (init) call doesn't look right. Usually it looks like :
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Here you could declare your setting.
}
return self;
}
But my opinion is that if you are declaring a singular pattern, you would call a specific method in your class, like you do with so many classes on the iOS/Cocoa, like :
[someclass DefaultClass]
This would be your init class where you would do init, unless the class had been declared before and then you would just return the object.
I'm implementing support for Lion's "Resume" feature in my OS X app.
I have a custom subclass of NSViewController in which I implemented the method
encodeRestorableStateWithCoder: as:
#implementation MyClass (Restoration)
-(void)encodeRestorableStateWithCoder:(NSCoder*)coder {
[coder encodeObject:_dataMember forKey:#"object_key"]; // I get the warning below when this line is executed for the second time
}
- (void)restoreStateWithCoder:(NSCoder *)coder {
_dataMember = [coder decodeObjectForKey:#"object_key"];
}
#end
However, since I have multiple instances of MyClass, different values are saved into the same key ("object_key") and I get the following warning from Cocoa:
NSKeyedArchiver warning: replacing existing value for key
'object_key'; probable duplication of encoding keys in class hierarchy
What is the best practice to overcome this problem?
Edit: I found here that each instance automatically has its own namespace to avoid collisions, so the problem might be in the way I'm manually calling encodeRestorableStateWithCoder to different instances with the same NSCoder object without telling it that these are different instances. However, I still can't figure out how to do that properly.
Thanks in advance!
To overcome this problem, it is possible to create a new NSMutableData where each of which is written by a separate (new) NSKeyArchiver, and store them all in an array which is stored in the original NSCoder object.
Here is an example for encoding the restorable state of subitems. The decoding part can be straight-forward given this code.
- (void)encodeRestorableStateWithCoder:(NSCoder *)coder
{
[super encodeRestorableStateWithCoder:coder];
// Encode subitems states:
NSArray* subitems = self.items;
NSMutableArray* states = [NSMutableArray arrayWithCapacity: subitems.count];
for (SubItemClass* item in subitems)
{
NSMutableData* state = [NSMutableData data];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:state];
[item encodeRestorableStateWithCoder:archiver];
[archiver finishEncoding];
[states addObject:state];
}
[coder encodeObject:states forKey:#"subitems"];
}
I have a singleton in my FTP app designed to store all of the types of servers that the app can handle, such as FTP or Amazon S3. These types are plugins which are located in the app bundle. Their path is located by applicationWillFinishLoading: and sent to the addServerType: method inside the singleton to be loaded and stored in an NSMutableDictionary.
My question is this:
How do I bind an NSDictionaryController to the dictionary inside the singleton instance? Can it be done in IB, or do I have to do it in code? I need to be able to display the dictionary's keys in an NSPopupButton so the user can select a server type.
Thanks in advance!
SphereCat1
I found / made up the answer to this: I simply override the init method so when it's called from the XIB file, it still returns the singleton. I then provide a method named realInit to do an actual initialization the first time init is called.
Code:
-(id)init
{
#synchronized(self)
{
if (_sharedInstance == nil)
{
_sharedInstance = [[VayprServerTypes alloc] realInit];
}
}
[self release];
return _sharedInstance;
}
-(id)realInit
{
if (self = [super init])
{
serverTypesArray = [[NSMutableArray alloc] init];
}
return self;
}
EDIT: Of course you'll need to define _sharedInstance as a static variable at the top of your class implementation:
static ClassTypeGoesHere *_sharedInstance;
ALSO EDIT: Since you now know for sure that your init method will be called at least once, you can go ahead and replace your normal singleton sharedInstance method with this:
+(ClassTypeGoesHere *)sharedInstance
{
return _sharedInstance;
}
If anyone sees any obvious problems with this design, please let me know!
SphereCat1