Subclassing UITextField / Delegate

[splitbrain]

Hi

I want to attach certain functionality to UI elements and to make it easier reusable I'd like to subclass the original UI elements. But it looks I'm missing something.

Here's what I did:

#import <UIKit/UIKit.h>
@interface UIMyField : UITextField <UITextFieldDelegate> {

}

- (id)initWithFrame:(CGRect)frame;
@end

#import "UIMyField.h"
@implementation UIMyField

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        self.delegate = self;
    }
    self.text = @"init";
    return self;
}

- (void)textFieldDidBeginEditing:(UITextField *)textField {
    textField.text = @"foo";
}

- (void)dealloc {
    [super dealloc];
}
@end

I then changed the class of a textfield in InterfaceBuilder to MyField but it seems that neither the initWithFrame nor the textFieldDidBeginEditing is ever called. What did I miss? Is there an example on how to subclass and extend core UI elements somewhere?

[beowulf573]

Try

- (id)initWithCoder:(NSCoder *)inCoder;

[splitbrain]

Excellent, initWithCoder worked :-). I assume initWithCoder is used when the class is instantiated by the InterfaceBuilder and initWithFrame when instantiating it yourself?

Thanks for your help.

- (id)initWithCoder:(NSCoder *)inCoder {
    if (self = [super initWithCoder:inCoder]) {
        self.delegate = self;
    }
    self.text = @"initcoder";
    return self;
}

[splitbrain]

Hmm looks like I called success too early :-( For some reason the program now freezes when I press a keyboard button.

The culprit seems to be the self delegation:

self.delegate = self;

Removing the line restores the keyboard functionality but my textFieldDidBeginEditing doesn't work anymore of course.

So what's the proper way to attach a default handler to this event to my subclass?

[beowulf573]

I was doing the exact same thing this weekend and ran into locking issues when implementing an empty shouldChangeCharactersInRange message. So far I've not come up with a solution but did read of other people experiencing it.

[CowTipper]

i don't think delegates were ever intended to be sent to self. if you're looking at creating a default handler that will be used whenever any instance of your subclassed UITextField is loaded, you can try making a small handler class, and then have it set that class as its delegate on init, ie:.

SomeClass.h:

@class DefaultHandlerClass

@interface SomeClass : UITextField

{
   DefaultHandlerClass *dClass;
}

@property (nonatomic,retain) DefaultHandlerClass *dClass

SomeClass.m:

@synthesize dClass;

//...

- (id)initWithCoder:(NSCoder *)inCoder {
    if (self = [super initWithCoder:inCoder]) {
        dClass = [[DefaultHandlerClass alloc] init]
        self.delegate = dClass;
    }
    self.text = @"initcoder";
    return self;
}

- (void)setDelegate:(id)aDelegate
{
  [self setDelegate:dClass];
  [dClass setDelegate:aDelegate];
}

- (id)delegate
{
  return [dClass delegate];
}

- (void)dealloc
{
   self.delegate = nil;
   if ( dClass != nil ) [dClass release];
   [super dealloc];
}

DefaultHandlerClass.h:

@interface DefaultHandlerClass <UITextFieldDelegate>

{
  id delegate
}

@property (nonatomic,assign) id delegate;

DefaultHandlerClass.m

@implementation DefaultHandlerClass

@synthesize delegate;

- (void)textFieldDidBeginEditing:(UITextField *)textField
{
   //...do your custom stuff here...
  
  //now forward message to this class' delegate
  if ( [delegate respondsToSelectore:@selector(textFieldDidBeginEditing:)] )
   {
      [delegate textFieldDidBeginEditing:textField];
   }
}

//... other delegate methods...

a little messy, and untested, but you get the idea.

[Paco]

Found a much easier way to do this:

You first need to create the delegate:

mydelegate.h:

#import <Foundation/Foundation.h>
@interface mydelegate : NSObject <UITextFieldDelegate>{}
- (void)textFieldDidEndEditingUITextField *)textField;
@end

mydelegate.m:
#import "mydelegate.h"
@implementation mydelegate
- (void)textFieldDidEndEditingUITextField *)textField
{
//do your stuff...
}
@end

Then, you need to create the class that extend the UITextField:

myTextField.h:

#import <UIKit/UIKit.h>
#import "mydelegate.h"
@interface myTextField : UITextField{}
@end


myTextField.m:

#import "myTextField.h"
@implementation myTextField
- (id)initWithFrameCGRect)frame
{
self = [super initWithFrame:frame];
if (self)
{
//Set the delegates to catch events
self.delegate = [[mydelegate alloc] init];
}
return self;
}
@end

And this is how is done!!