如何自定义按钮的各种状态下的显示，

通过对基类uicontrol的控制实现的
- (void)commonInit {
    [self setImage:[UIImage imageNamed:@"Normal"] forState:UIControlStateNormal];
    [self setImage:[UIImage imageNamed:@"Selected"] forState:UIControlStateSelected];
    [self setImage:[UIImage imageNamed:@"Highlighted"] forState:UIControlStateHighlighted];
    [self setImage:[UIImage imageNamed:@"Selected_Highlighted"] forState:UIControlStateSelected | UIControlStateHighlighted];
}