CODEWITHSUNDEEP
objective-c
Curnelious
Curnelious

Reputation: 1

A very scary message from iOS

Lately i am sometimes getting this very strange message during operation of my app, with no crash. (mainly the app now just get images from the net ) . I thing it has to do with me drawing a rect around image , the message is :

<Error>: CGContextStrokeRect: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context  and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.

the rect drawing :

-(UIImage*)imageWithBorderFromImage:(UIImage*)source
{

    CGSize size = [source size];

    UIGraphicsBeginImageContext(size);
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    [source drawInRect:rect blendMode:kCGBlendModeNormal alpha:1.0];

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetRGBStrokeColor(context,(255/255.f),(255/255.f),(255/255.f), 1.0);
    CGContextStrokeRect(context, rect);
    UIImage *testImg =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return testImg;
}

Upvotes: 0

Views: 235

Answers (3)

Rich
Rich

Reputation: 8202

You're [source size] is possibly occasionally CGSizeZero - put a check in and return nil.

+(UIImage*)imageWithBorderFromImage:(UIImage*)source
{
    CGSize size = [source size];

    if (CGSizeEqualToSize(size, CGSizeZero)) {
        return nil;
    }

    UIGraphicsBeginImageContext(size);
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    [source drawInRect:rect blendMode:kCGBlendModeNormal alpha:1.0];

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetRGBStrokeColor(context,(255/255.f),(255/255.f),(255/255.f), 1.0);
    CGContextStrokeRect(context, rect);
    UIImage *testImg =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return testImg;
}

You can simiplify your above code by the way using the newer non-CG methods - this shows that you do not need to use CGContext directly...

+(UIImage*)imageWithBorderFromImage:(UIImage*)source
{
    CGSize size = [source size];

    if (CGSizeEqualToSize(size, CGSizeZero)) {
        return nil;
    }

    UIGraphicsBeginImageContext(size);
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    [source drawInRect:rect blendMode:kCGBlendModeNormal alpha:1.0];
    [[UIColor whiteColor] setStroke];
    UIRectFrame(rect);
    UIImage *testImg =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return testImg;
}

EDIT: I've also made your methods class methods as there is no reason to use an instance method - unless you want to call [source imageWithBoarder] instead - in my opinion this is a bit neater :)

Upvotes: 1

Taylor Halliday
Taylor Halliday

Reputation: 640

The call to UIGraphicsGetCurrentContext() is probably returning nil.

As for your stated goal though, I think you would be better off skipping the CoreGraphics drawing route, and instead putting your UIImage in a UIImageView. If you're trying to give it a border, assign the UIImageView's layer.borderWidth and layer.borderColor properties some values. Taken out of context though, it's tough to see what you're doing, so this may/may not be the solution to your problem.

Upvotes: 2

FreeAsInBeer
FreeAsInBeer

Reputation: 12979

I would highly discourage you from using the method you're using. Drawing images yourself is verbose, error prone and less maintainable. Instead, I recommend you use an UIImageView. You can then place your drawing code within the UIImageView's drawRect method as described here. Otherwise, your graphics context will be nil.

Performing drawing outside of the drawRect method is highly discouraged.

Upvotes: 1

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