Help with Showing and Hiding a UIImage

lukeirvin · January 2012

I'm working on adding a QR code in an app.

I'd like to have it set to only show the image when something has been placed in a UITextField

I'm trying something like this:


if ( (string = [NSString stringWithFormat:@\"%@\", aTextField.text]) )
{

        UIImage * image = [QREncoder encode:string];
    
        aImageView = [[UIImageView alloc] initWithImage:image];

        .... more code

       [aViewController.view addSubview:aImageView];
    
       [aImageView release];
}
    
else
{
     [self.aImageView removeFromSuperview];
}

The image is always there though

Any ideas to what I'm doing wrong?

msencenb · January 2012

I believe this:

if ( (string = [NSString stringWithFormat:@"%@", aTextField.text]) )

Will always evaluate to true because the stringWithFormat will return an "empty string" even if there is no text.

Perhaps try something more like this:


string = [NSString stringWithFormat:@\"%@\", aTextField.text]
if ([string length] != 0) {

}

lukeirvin · February 2012

makes much more sense, but the image is still always showing :(

msencenb · February 2012

lukeirvin;405834 said:
makes much more sense, but the image is still always showing :(

Is the text field hooked up correctly?

lukeirvin · February 2012

Yes I believe so. Should string be a property and synthesized?

If I do this [string length] == 0, then the image never shows no matter what

But if i try != or > it always shows

msencenb · February 2012

oh sorry. String should be a local variable. (Also I don't like the variable name string)

NSString *text = [NSString stringWithFormat:@\"%@\", aTextField.text]
if ([text length] != 0) {

}

lukeirvin · February 2012

still always shows image

msencenb · February 2012

Ok let's try a different tactic:

if ([aTextField.text isEqualToString:@\"\"]) {

} else {

}

lukeirvin · February 2012

got it working! Used that method and had to change one line of code.

Thank you much for you help :)

lukeirvin · February 2012

Found a new issue:

If I leave the text field empty no QR Image appears

If I enter in text, a QR Image will appear. If I go back and remove the text then proceed, the QR Image is still there.

Everything I have tried so far hasn't fixed this... Tried releasing it in a couple of places but that was not the case.

Thoughts?

Duncan C · February 2012

lukeirvin;406093 said:
Found a new issue:

If I leave the text field empty no QR Image appears

If I enter in text, a QR Image will appear. If I go back and remove the text then proceed, the QR Image is still there.

Everything I have tried so far hasn't fixed this... Tried releasing it in a couple of places but that was not the case.

Thoughts?

Add a log statement:

NSLog(@\"aTextField.text = '%@'. length = %d\", aTextField.text, [aTextField.text length]);

Then your if statement:

if ([aTextField.text length] != 0)
{
  //generate a QR code
}
else
{
  clear out the QR code
}

Then run the program and see what you are getting in the console log when you type in something, then try to erase it.

That will let you figure out what's going wrong.

RickSDK · February 2012

i can't tell if you are saying your triggering code is off or your "make image disappear" code is not working, but to make an image disappear I usualy use this line:

aImageView.alpha=0;

lukeirvin · February 2012

malloc: *** error for object 0x8ac0260: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

lukeirvin · February 2012

Never mind on that one. I was releasing the object too many times.

Looking great now! Thanks for the help :)

Narender Mudgal · February 2012

I don't know if you did it knowingly but in if loop you were using assignment operator = not comparison operator == so it will assign something like empty string to string variable and the statement will be true so it will always go in.

lukeirvin · February 2012

Right, I knew to avoid that :)

One last question. The image is being generated when I want and it looks great on screen. But when I email it or save it the image becomes blurry. Has anyone had an issue like this before? I tried doing the same method as before to make the image sharper but that did not work :-/

Duncan C · February 2012

RickSDK;406102 said:
i can't tell if you are saying your triggering code is off or your "make image disappear" code is not working, but to make an image disappear I usualy use this line:

aImageView.alpha=0;

You should use aImageView.hidden=true instead.

That takes disables it and cleanly hides it, rather than forcing the graphics engine to composite the image with the surroundings, like it has to do when the alpha is not 1.0

lukeirvin · February 2012

Still haven't found a solution to my blurry image.

I'm having the same issue this developer is having:

objective c - kCAFilterNearest maginifcation filter (UIImageView) - Stack Overflow

I have tried the recommended method:



    aImageView.frame = CGRectIntegral(aImageView.frame);

but no luck. Any thoughts on what to try?

Duncan C · February 2012

lukeirvin;406259 said:
Right, I knew to avoid that :)

One last question. The image is being generated when I want and it looks great on screen. But when I email it or save it the image becomes blurry. Has anyone had an issue like this before? I tried doing the same method as before to make the image sharper but that did not work :-/

Post the code that you are using to export the image. My guess is that you are saving it to a different size and/or JPEG compressing it, both of which will result in a loss of image quality.

lukeirvin · February 2012

This makes my QR image:


        UIImage * image = [QREncoder encode:aTextField.text];
    
        aImageView = [[UIImageView alloc] initWithImage:image];
    
        CGFloat aSize = self.view.bounds.size.width - kPadding * 13;
    
        aImageView.frame = CGRectMake(605, 20, 100, 100);
    
        aImageView.frame = CGRectMake(kPadding, (self.view.bounds.size.height - aSize) / 2, aSize, aSize);
    
        [aImageView layer].magnificationFilter = kCAFilterNearest;
            
        aImageView.center = CGPointMake(680, 80);
    
        [secondVeiwController.view addSubview:aImageView];

In my second view a user can email a PDF attachment that has the image among other information in it. The image becomes blurry in the PDF

lukeirvin · February 2012

Thoughts on this?

Do I need to be doing any image code when making my PDF?

lukeirvin · February 2012

This is where I make my PDF (forgot to include this):


    NSMutableData * pdfData = [NSMutableData data];
    UIGraphicsBeginPDFContextToData(pdfData, self.view.bounds, nil);
    UIGraphicsBeginPDFPage();
    CGContextRef pdfContext = UIGraphicsGetCurrentContext();
    [secondViewController.layer renderInContext:pdfContext];
    UIGraphicsEndPDFContext();

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