按钮的不同状态显示记录一下
[btn setTitle:@"正常" forState:(UIControlStateNormal)];
[btn setTitle:@"高亮" forState:(UIControlStateHighlighted)];
[btn setTitle:@"选中" forState:(UIControlStateSelected)];
[btn setTitle:@"选中高亮" forState:(UIControlStateSelected | UIControlStateHighlighted)];
[btn addTarget:self action:@selector(btnClick:) forControlEvents:(UIControlEventTouchUpInside)];