Android：错误-案例表达式必须是常量表达式

Question

I have been working on an app, and recently got a new computer. I had to import my existing code into this computer. Now, when I do this I get a few errors in the build path, so I fix them. But now, I get errors in every case in my switch and case. It says: case expressions must be constant expressions.

An example of my code:

case R.id.b3:
    a.putExtra("Green", "green");
    startActivity(a);
    break;
case R.id.b4:
    a.putExtra("Pink", "pink");
    startActivity(a);
    break;

I get the errors on the ids of the button. Everything worked fine on the other computer I used, so I'm not sure why I now get this error. I did google it and I read I should replace them all with an if else statement, but that would be a major pain to replace all my switch and cases, so I'd want to avoid that.

Why this happens on my imported code?

Answer 1

This happens when your resources are defined in a library project. I believe one of the newer versions of the Android plugin requires this based on changes to the way library projects are compiled. The if-else is necessary. The IDE will do it for your automatically. If you highlight the switch keyword and press ctrl-1 you should get an option to make the change automatically.

You can read about it here .

Answer 2

Check the activity you are working with , the one that gives you the errors, and look up this line of code in it

import android.R;

delete it! perform clean and everything should work

Answer 3

自从ADT14 更改了工具链后不久以来，就没有保证id在库中是恒定的。

Answer 4

这可能是您正在使用third_party库，为了使您能够快速开发应用程序并能够使用多个库，资源ID未定义为final，因此您必须使用if / else而不是switch / case 。