UIView subclass: drawRect not called

Question

I am a beginner in iOS programming, so sorry if my question is a stupid question.

I am trying to make an app which performs custom drawing on a loaded image.

To do it, I found out that a solution is to subclass UIView and edit the drawRect method.

I made that on the following code which activates on an IBAction linked to a button in the Interface Builder storyboard file.

UIImageView *image = [[UIImageView alloc] initWithImage: [UIImage imageNamed:     @"SampleImage.jpg"]]; 
image.frame = previewView.frame;
[image setContentMode:UIViewContentModeScaleAspectFit];       

[previewView addSubview:image];

customView *aCustomView = [[customView alloc] initWithFrame: CGRectMake(image.bounds.origin.x, image.bounds.origin.y, image.bounds.size.width, image.bounds.size.height)];
[previewView addSubview:aCustomView];

customView is the UIView subclass that I created, whose init and drawRect methods are set like this:

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    NSLog(@"INITIALIZING");
    if (self) {
        // Initialization code
        [self setBackgroundColor:[UIColor clearColor]];
    }
    return self;
}


- (void)drawRect:(CGRect)rect
{
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    NSLog(@"DRAWING");

    CGContextClearRect(ctx, rect);

    CGContextSetRGBFillColor(ctx, 0, 255, 0, 0.3);
    CGContextFillEllipseInRect(ctx, rect); 

    CGContextSetRGBStrokeColor(ctx, 255, 0, 0, 1);
    CGContextSetLineWidth(ctx, 2);
    CGContextStrokeEllipseInRect(ctx, rect);
}

The problem that I have is that no drawing is made and on NSLog I have the "INITIALIZING" message, but not the "DRAWING" drawing.

So basically it makes the initWithFrame, but it doesn't call the drawRect method.

Could you please point me what am I doing wrong?

Answer 1

1. Make sure your new view class is subclassing the UIView, not the UIImageView.
2. To make sure the new view is showing up, you will need to do [viewContainer addSubView:] to get the drawRect to be called.

Ref from the doc:

The UIImageView class is optimized to draw its images to the display. UIImageView will not call drawRect: a subclass. If your subclass needs custom drawing code, it is recommended you use UIView as the base class.

https://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIImageView_Class/Reference/Reference.html

Answer 2

Paolo,

Here are a few things you can try:

1. in initWithFrame, check that the frame variable contains what you would expect it to: NSLog(@"Frame: %@", NSStringFromCGRect(frame));
2. Try calling [preview setNeedsDisplay]; after adding it to its superview

Lastly, I would change

image.frame = previewView.frame;

with:

image.bounds = CGRectMake(0, 0, previewView.frame.size.width, previewView.frame.size.height);

Answer 3

May be the question is aCustomView's frame is (0,0,0,0).
You can try to pass a constant CGRect param, like this : CGRectMake(5, 5, 100, 100)。