IOS_UIButton去掉系统的按下高亮置灰效果

setAdjustsImageWhenHighlighted // default is YES. if YES, image is drawn darker when highlighted(pressed)

_foldOrOpenButton = [UIButton buttonWithType:UIButtonTypeCustom];

[_foldOrOpenButton addTarget:self action:@selector(foldOrOpen:) forControlEvents:UIControlEventTouchUpInside];