how implement radio button behavior?

I have two UIButtons. they behave like check boxes(both buttons can select at a time). But I want only one 开发者_运维百科button can select at a time (like radio buttons). How can I do it? This how I implement checkbox button feature.

if ([btnAnswer1 isSelected]) {
        [btnAnswer1 setBackgroundImage:[UIImage imageNamed:@"checkbox_unchecked.png"] forState:UIControlStateNormal];
        [btnAnswer1 setSelected:NO];

    }else {
        [btnAnswer1 setBackgroundImage:[UIImage imageNamed:@"checked.png"] forState:UIControlStateSelected];
        [btnAnswer1 setSelected:YES];
    }



    if ([btnAnswer2 isSelected]) {
        [btnAnswer2 setBackgroundImage:[UIImage imageNamed:@"checkbox_unchecked.png"] forState:UIControlStateNormal];
        [btnAnswer2 setSelected:NO];
    }else {
        [btnAnswer2 setBackgroundImage:[UIImage imageNamed:@"checked.png"] forState:UIControlStateSelected];
        [btnAnswer2 setSelected:YES];
    }

The way I usually implement radio buttons is:

-(void) radioButtonWasSelected:(RadioButton*) which
{
    //set all radio buttons to unselected
    //set 'which' to selected

    //do something with 'which'

}

Though I haven't check, just try with given modified code.

    if ([btnAnswer1 isSelected]) 
    {
        [btnAnswer1 setBackgroundImage:[UIImage imageNamed:@"checkbox_unchecked.png"] forState:UIControlStateNormal];
        [btnAnswer1 setSelected:NO];
        selected = FALSE;
        [btnAnswer2 setBackgroundImage:[UIImage imageNamed:@"checked.png"] forState :UIControlStateSelected];
        [btnAnswer2 setSelected:YES];
    }
    else 
    {
        [btnAnswer1 setBackgroundImage:[UIImage imageNamed:@"checked.png"] forState: UIControlStateSelected];
        [btnAnswer1 setSelected:YES];
        [btnAnswer2 setBackgroundImage:[UIImage imageNamed:@"checkbox_unchecked.png"] forState: UIControlStateNormal];
        [btnAnswer2 setSelected:NO];
        selected = TRUE;
    }

    if ([btnAnswer2 isSelected]) 
    {
        [btnAnswer2 setBackgroundImage:[UIImage imageNamed:@"checkbox_unchecked.png"] forState: UIControlStateNormal];
        [btnAnswer2 setSelected:NO];
        [btnAnswer1 setBackgroundImage:[UIImage imageNamed:@"checked.png"] forState: UIControlStateSelected];
        [btnAnswer1 setSelected:YES];
    }
    else 
    {
        [btnAnswer2 setBackgroundImage:[UIImage imageNamed:@"checked.png"] forState: UIControlStateSelected];
        [btnAnswer2 setSelected:YES];
        [btnAnswer1 setBackgroundImage:[UIImage imageNamed:@"checkbox_unchecked.png"] forState: UIControlStateNormal];
        [btnAnswer1 setSelected:NO];
    }