UIButton上的标签类型UIButtonTypeCustom没有显示

I want to add a borderless UIButton to my view. Using the interface builder, I do this by dragging a Round Rect Button from the object library. Then, on the attributes inspector, change the Type to Custom and leave the title to "Button." Everything is okay with the interface builder. But, this is not the case with the programmatic approach. Programmatically, this is how I do it:I want to add a borderless UIButton to my view.