Objective-C exam [closed]

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I had a job interview yesterday and they said list all thats wrong with this code: Think I got most but not sure...

MyView.h:

#import "UIKit.h"

@interface MyView : UIView {
  NSString* name;
  UIButton* button;
}           

@property(assign, copy) NSString* dateString;
@property(nonatomic, retain) UIButton* button;

- (void)buttonPressed;     

@end

MyView.m:

#import "MyView.h"           

@implementation MyView      

@synthesize dateString, button;           

- (id)init {
  self = [super init];
  if (self != nil) {
    button = [UIButton initWithFrame:CGRectMake(0, 0, 50, 50)];
    [button setImage:[UIImage imageNamed:@"buttonImage.png"] forState: UIControlStateNormal];
    [button addTarget:self 
               action:@selector(buttonPressed)
     forControlEvents:UIControlEventTouchUpInside];
    [button release];
    [self addSubview:button];

    NSDateFormatter *headerDateFormatter = [[[NSDateFormatter alloc] init] autorele开发者_如何学Case];        
    [headerDateFormatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease]];       
    [headerDateFormatter setDateFormat:@"EEE, d MMM yyyy HH:mm:ss Z"];
    [self setDateString:[headerDateFormatter stringFromDate: [NSDate date]]];
    [headerDateFormatter release];               

    for(NSInteger i=0; i<=10; i++){       
      NSLog(@"i = ", i);          
    }                
}

-(void)buttonPressed {
  NSLog(dateString);      
}

- (void)dealloc {
  [button removeFromSuperView];
  [button release];
  [dateString release];
  [super dealloc];
 } 

---

Answer:

==========

[headerDateFormatter release];

not necessary as already autoreleased

==========

NSLog(@"i = ", i);          

should be

NSLog(@"i = %d", i);         

==========

 [button release];
          [self addSubview:button];

WRONG WAY ROUND

[self addSubview:button];   //addSubView retains button
[button release];           //so release after

=========

NSLog(dateString); 

NSLog(@"%@",dateString); 

=========

          - (void)dealloc {
          [button removeFromSuperView];   //unnecessary - whole view is about to be dealloc'd no need to break it apart

=========

you could also set images for other states for the button you only set it for one

  [button setTitle:title forState:UIControlStateNormal];

        [button setTitle:title forState:UIControlStateHighlighted];

        [button setTitle:title forState:UIControlStateSelected];

=========

- (void)buttonPressed {

Event handler
- (void)buttonPressed:(UIButton *)button {

---

Lots of things wrong...

#import "UIKit.h"

Should be #import <UIKit/UIKit.h>

@interface MyView : UIView {
  NSString* name;
  UIButton* button;
}           

@property(assign, copy) NSString* dateString;

Should be (nonatomic, copy)

@property(nonatomic, retain) UIButton* button;

- (void)buttonPressed;     

@end

The rest looks reasonable.

#import "MyView.h"           

@implementation MyView      

@synthesize dateString, button;           

- (id)init {
  self = [super init];

This should be calling the designated initializer: initWithFrame:

  if (self != nil) {
    button = [UIButton initWithFrame:CGRectMake(0, 0, 50, 50)];

This should probably be self.button = ...; Also, there's no +initWithFrame: method. It's -initWithFrame:.

    [button setImage:[UIImage imageNamed:@"buttonImage.png"] forState:UIControlStateNormal];
    [button addTarget:self 
               action:@selector(buttonPressed)
     forControlEvents:UIControlEventTouchUpInside];
    [button release];

The button should not be released, since we do not have an owning reference to it. If we used self.button = ... above, then we still wouldn't release it here, because the property is declared as retain.

    [self addSubview:button];

    NSDateFormatter *headerDateFormatter = [[[NSDateFormatter alloc] init] autorelease];        
    [headerDateFormatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease]];       
    [headerDateFormatter setDateFormat:@"EEE, d MMM yyyy HH:mm:ss Z"];
    [self setDateString:[headerDateFormatter stringFromDate: [NSDate date]]];
    [headerDateFormatter release];     

The extra release on the formatter is wrong, since we autorelease'd it already.

    for(NSInteger i=0; i<=10; i++){       
      NSLog(@"i = ", i);          

This is missing the %d (or %i or whatever)

    }                
}

The return self; statement is missing.

-(void)buttonPressed {
  NSLog(dateString);      

You shouldn't ever log strings directly. This should be NSLog(@"%@", dateString);

}

- (void)dealloc {
  [button removeFromSuperView];

This is unnecessary, but is fine to have here.

  [button release];

This is technically incorrect since we never retained button in the initializer. However, if we fixed the initializer to correctly retain the button, then this is correct.

  [dateString release];
  [super dealloc];
 } 

Also, the name ivar is never used.

---

A few more:

• The ivar name is never used and should be removed.

• The for loop in -init doesn't do anything useful (except provide a forum for the incorrect NSLog()) and should be removed.

• The designated initializers for UIView are -initWithFrame: and -initWithCoder:. At the very least, MyView's -init should call either [self initWithFrame:] or [super initWithFrame:], but it would be better to just override -initWithFrame: in the first place.

• -buttonPressed should not return dateString directly, but should instead use the property accessor: self.dateString

A couple that you got wrong:

• The [button release]; in -init isn't just in the wrong place, it's just plain wrong. The button property is marked retain, so the object should not release the button (assuming it was properly alloc'ed in the first place) in -init. If you fix the order of the -retain and -addSubView: in -init, the code will work until either the button setter or -dealloc releases the button again, at which point you'll probably crash.

• The -buttonPressed method is fine as an action -- no need to make it -(void)button:(UIButton*)button. In Cocoa Touch, actions can take zero, one, or two parameters. It would be nice, however, if the action were marked with IBAction to better communicate its purpose.

---

#import "UIKit.h" 

should be

#import <UIKit/UIKit.h>

and

button = [UIButton initWithFrame:CGRectMake(0, 0, 50, 50)]; was never alloced.

---

You are missing

@property(assign, copy) NSString* dateString; 

You cannot have the property as both assign and copy.

---

That button init also doesn't have the alloc call before initWithFrame. While you're on the button, I don't even know if button has that method. As of current sdk, you would use the class method UIButton buttonWithType to init a button.

---

Another error - dateString is property, it should be called with self. Also seems to be to link it with some class field or getter metod