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PREAMBLE: this question is quite obsolete, it was written when the preferred Android dev environment was Eclipse with the Android plugin.

I had a Java Android project for a while. Today, I've updated the Android dev tools to the Google's latest. And the project broke - I get a bunch of "case expressions must be constant expressions" compilation error messages.

Turns out that the R.java file is being now generated differently. Formerly, it would have a bunch of

public static final int MyID=0x12340000;

statements; now, it looks (after a clean/rebuild) like this:

public static int MyID=0x12340000;

final is gone. So all switches on resource IDs that I had (and I had a few) are wrong. What happened, please? Is it just me? What's the rationale here? Is it documented anywhere? Can I bring final back somehow?

Seva Alekseyev
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5 Answers5

40

This happened about yesterday, when the SDK/ADT 14 got released:

As of ADT 14, resource constants in library projects are no longer final. This is explained in greater detail in http://tools.android.com/tips/non-constant-fields

There's a quickfix available from ADT 14: http://tools.android.com/recent/switchstatementconversion

To quote from the rationale:

When multiple library projects are combined, the actual values of the fields (which must be unique) could collide. Before ADT 14, all fields were final, so as a result, all libraries had to have all their resources and associated Java code recompiled along with the main project whenever they were used. This was bad for performance, since it made builds very slow. It also prevented distributing library projects that didn't include the source code, limiting the usage scope of library projects.

The reason the fields are no longer final is that it means that the library jars can be compiled once and reused directly in other projects. As well as allowing distributing binary version of library projects (coming in r15), this makes for much faster builds.

Philipp Reichart
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    Makes sense, actually. I see where they're coming from. The fact that Android libraries were just linked sources as opposed to, well, compiled libraries, has been a minor pain point for me for some time. Also, kudos to Google for providing a magic refactorer. – Seva Alekseyev Oct 20 '11 at 19:27
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    This is just a consequence of an idiotic design decision by the Android team. Whenever you see some generated file with a bunch of magic number constants, you should look at it funny. Thanks, Google for breaking a bunch of your developers' source code due to complete lack of foresight. Public static ints. Much better?! – Nate Nov 12 '11 at 01:15
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    This answer is marked as solution - but I don't see it... Very nice discussions, suggestions, documentation links and etc only... What is concrete solution? What should I change in my code to fix the issue - please in a few words? Or no solution? - then please answer in one word: "no". ? – Vitaly Dec 25 '20 at 05:56
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    @RussiaDroneFlights Did you read any of the links? They say to use if-else clauses instead of switch statements if you need to do someting conditionally with resource IDs. Switch statements would require the IDs to be final, which they haven't been for slightly over nine years now. – Philipp Reichart Dec 26 '20 at 11:40
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You could switch over to using If/Else statements and the warning will go away.

Sample:

    @Override
    public void onClick(final View v) {
        //finds which button was pressed
        final int buttonView = v.getId();
        String current = fromEditText.getText().toString();
        if (buttonView == R.id.bA) {
            current += getString(R.string.a);
        }
A Pars
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5

Google recommends you use if/else conditions

http://tools.android.com/tips/non-constant-fields

To change them automatically you can place the caret on the switch keyword and press Alt + Enter on Windows (Option + Enter on Mac) and select Replace 'switch' with 'if'

DJTano
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2

You should use view binding!

android {
    ...
    viewBinding {
        enabled = true
    }
}
Muse
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1

Just add this snipped in your module-level build.gradle file:

android {
    ...
    lintOptions {
        disable 'NonConstantResourceId'
    }
}

More: https://developer.android.com/studio/write/lint#gradle

Andrei Andrushchak
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