Weird appearance about button selected

Question

I'm sure I set right images for different states. But the UIButtons looks not good. Like this:

Anyone knows why? Many thanks in advance!

Answer 1

从system更改为Custom然后尝试，

[UIButton buttonWithType:UIButtonTypeCustom]; 

Answer 2

我没有在所有状态下都输入任何单词（包括空格），我将颜色设置为白色，但效果很好，我认为这可能是由于自动布局引起的。