UIButton根据不同的状态设置layer 这需要用到KVO，监听button的highlighted属性的变化，在监听回调里根据监听到的属性值设置layer
设置监听如下
[button addObserver:self forKeyPath:@"highlighted" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
监听回调如下
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
UIButton * bt = (UIButton* )object;
if([keyPath isEqualToString:@"highlighted"])
{
if(bt.state == UIControlStateNormal) {
bt.layer.bordColor = [UIColor redColor].CGColor;
} else{
bt.layer.bordColor = [UIColor black].CGColor;
}
}
