UIButton with custom Type seems not to work properly

Question

something strange happened during the development of my app. I have a view with several UIButtons in it. All are using custom artwork and are UIButton with CostumType. For me everything felt right. In the simulator and on the phone.

But when I give the app in someone else's hand the person taps on a button and it won't work. It feels like the button is just reaction to a certain tap which in fact doesn't feel right (if you compare it to normal behavior).

What can I do to make it behave normal? Normal means that somebody who is used to iOS Apps can use it like he except it works.

Here is an example code for a button:

focusButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [focusButton setFrame:CGRectMake(self.bounds.size.width-(self.bounds.size.width/widthFactor)+108, self.bounds.origin.y+(self.bounds.size.height/(heightFactor*2))+2, 36, 40)];
    focusButton.contentHorizontalAlignment = false; // I think these lines doesn't effect the behavior
    focusButton.contentVerticalAlignment = false;
    [focusButton setBackgroundImage:[UIImage imageNamed:@"arrowUp.png"] forState:UIControlStateNormal];
    [focusButton setBackgroundImage:[UIImage imageNamed:@"arrowUpH.png"] forState:UIControlStateHighlighted];
    [focusButton addTarget:self action:@selector(focusOrDefocusCourse) forControlEvents:UIControlEventTouchUpInside];
    [self addSubview:focusButton];

The Button Background looks like this:

Answer 1

You may like to take a look at the UIButton property imageEdgeInsets. This allows you to make the image draw into only part of the frame, so that the touchable area is bigger than the image itself (reducing the chance of 'missing' the button). You could do the following, for example:

int touch_offset = 10;
[focusButton setFrame:CGRectMake(self.bounds.size.width-(self.bounds.size.width/widthFactor)+108-touch_offset, self.bounds.origin.y+(self.bounds.size.height/(heightFactor*2))+2-touch_offset, 36+(touch_offset*2), 40+(touch_offset*2))];
focusButton.imageEdgeInsets = UIEdgeInsetsMake(touch_offset, touch_offset, touch_offset, touch_offset);

This should make the touchable area 10 pixels wider than the image on each side, adjustable by changing the touch_offset value. As a general guideline, Apple recommend using touchable areas no smaller than 44x44 pixels.