我无法为我的应用中的下一个按钮添加功能。它应该在每次按下时更改文本。

I cannot add functionality to the next button in my app. It should change the text every time it's pressed. Though, in my case, what it does is change the text for once and then goes to sleep! What should I do? I searched the website but couldn't find any way!I cannot add functionality to the next button i