R – Overload method (specifically drawRect:) without subclassing

overloadingsubclassinguiview

I'm using a container UIView to house a UIImageView and do some custom drawing. At this point I'd like to do some drawing on top of my subview. So overriding drawRect: in my container UIView will only draw below the subviews.

Is there a way to overload drawRect: in my subview without subclassing it?

I think method swizzling may be the answer, but I'm hoping not.

(NOTE: yes, it would have been smarter to have the UIView be the subview of the UIImageView, but unfortunately I'm committed to my mistake now.)

Best Answer

Are you sure you mean overload and not override?

Overloading -- creating a new method with the same basic name but different arguments and therefore a different selector -- could be accomplished by adding a new method category containing your new method to the existing class.

Overriding -- modifying the behavior of an existing method -- would require either monkey-patching the class's method table at runtime (for example, by swizzling) or subclassing.

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Iphone – Need to override drawrect if your UIView is merely a container

Your subviews should have their frame initialized to the bounds of the parent uiview. Subviews are in a different coordinate system that is relative to the frame of the parent.

self.onLight = [[[LoyaltyCardNumberView alloc] initWithFrame:self.bounds] autorelease];

IOS: Drawing line is appearing behind subviews

Make another custom view, that has the only job of drawing the line. Add it as a subview with the same frame as the ImageView, and call bringSubviewToFront to make sure it's in front. You might have to set some attributes on your custom view like opaque = NO and set the background color to clear ([UIColor colorWithWhite:0.0 alpha:0.0]).

By the way, don't add any subviews in drawRect. drawRect should just draw, not change the view attributes or hierarchy. You should add the ImageView and the custom line drawing view somewhere else, maybe in the init. Like so:

@implementation MyView

-(id)initWithFrame:(CGRect)frame {
    if ((self = [super initWithFrame:frame])) {
        imageView = ... // however you create your image view
        [self addSubview:imageView];
        lineView = [[MyLineView alloc] initWithFrame:imageView.frame];
        [self addSubview:lineView];
        [self bringSubviewToFront:lineView];
    }
    return self;
}

...

@end

@implementation MyLineView

-(void)drawRect:(CGRect)rect {
    // your drawing code
    // remember the coordinate system now has (0, 0) at the top left corner of the
    // image view, so adjust your drawing code accordingly
}

@end

Best Answer

Related Solutions

Iphone – Need to override drawrect if your UIView is merely a container

IOS: Drawing line is appearing behind subviews

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