UIButton在不同状态下的设置:
UIControlStateNormal 正常状态
UIControlStateHighlighted 高亮状态,按钮按下时状态,在正常状态时按下
UIControlStateSelected 选中状态
UIControlStateSelected|UIControlStateHighlighted 高亮状态,按钮按下时状态,在选中状态时按下
例如:
[btn setImage: forState:UIControlStateNormal];
[btn setImage: forState:UIControlStateHighlighted];
[btn setImage: forState:UIControlStateSelected];
[btn setImage: forState:UIControlStateSelected|UIControlStateHighlighted];