How to check if a uiimage view is added on a UIButton - iphone

Question

I have taken all the images from photo gallery in an array and then shown all these images on UIButtons and putt them in scroll View to show a grid view.Now when user click the button it should look like as he selected that image, for that I have taken a tick mark image and added it in a UIImageView and added that image view on the button on its click. But now when user again click the same button then how to remove that UIImageview from button when user has already selected multiple images.
Here is my code
-(void)loadImagesOnScrollView
{
scrollView.contentSize=CGSizeMake(0, 55*[assets count]);
int x=0,y=0;
for (int i=0; i<[assets count]; i++) {
ALAsset *asset = [assets objectAtIndex:i];
UIButton *btn=[UIButton buttonWithType:UIButtonTypeCustom];
btn.frame=CGRectMake(x, y, 100, 100);
btn.tag=i;
[btn setImage:[UIImage imageWithCGImage:[asset thumbnail]] forState:UIControlStateNormal];
[btn addTarget:self action:#selector(btnClkd:) forControlEvents:UIControlEventTouchUpInside];
if(i==0)
{
}
else if(i%2 ==0)
{
x=0;
y=y+110;
}
else
{
x=x+110;
}
[scrollView addSubview:btn];
}
}
-(void)btnClkd:(UIButton*)sender
{
if (sender.selected) {
sender.selected=FALSE;
}
else
{
sender.selected=TRUE;
}
if(sender.selected)
{
[sender addSubview:imgView];
}
else
{
}
}
Along this I have one more question, how to set the content size of scroll view so as it can be adjusted with any number of images.

Answer 1

when you add an image on a button on selection, set its tag = constant (say 9999) + sender.tag.
Now again on click of button check if subview with tag 9999+sender.tag exists. If yes, remove that subview from superview

Answer 2

Create a BOOL variable in your .h file eg:
BOOL isButtonClicked; // in .h file
then in your .m file
-(IBAction)onButtonClick:(UIButton *)checkBoxButton
{
if (!isButtonClicked) {
[checkBoxButton setImage:[UIImage imageNamed:#"tickMark.png"] forState:UIControlStateNormal];
isButtonClicked=YES;
}
else
{
[checkBoxButton setImage:[UIImage imageNamed:#"NormalImage.png"] forState:UIControlStateNormal];
isButtonClicked=NO;
}
}

Answer 3

To check if UIImageView is added to an UIButton use the following..
for check if the button has any UIImage
if ( [button.currentImage isEqual:[NSNull null]]) {
NSLog(#"image exist");
}
or
for check if the button has any background Image
if ( [button.currentBackgroundImage isEqual:[NSNull null]]) {
NSLog(#"background image exist");
}