Android Question - "Id cannot be resolved or is not a field" error?

Question

I keep getting this error... should I just make "id" a field? My code:

public void onCreate(Bundle icicle) {  
     super.onCreate(icicle);  
     setContentView(R.layout.main); 

     ImageView mainimage = (ImageView) findViewById(R.id.mainanim); 
     mainimage.setBackgroundResource(R.anim.mainanim); 
     mainanimation = (AnimationDrawable) mainimage.getBackground(); 

How exactly do you fix this?

Answer 1

Do not modify the R class. The error means there's something syntactically wrong with your XML layouts and R cannot be auto-generated. Try looking there and post the xml code you're not sure about, if any.

Answer 2

Look at your import statements at the top. If you are saying import android.R, then there that is a problem. It might not be the only one as these 'R' errors can be tricky, but it would definitely definitely at least part of the problem.

If that doesn't fix it, make sure your eclipse plugin(ADT) and your android SDK are fully up to date, remove the project from the emulator/phone by manually deleting it from the OS, and clean the project (Launch Eclipse->Project->Clean...). Sounds silly to make sure your stuff is fully up to date, but the earlier versions of the ADT and SDK has a lot of annoying bugs related to the R files that have since been cleared up.

Just FYI, the stuff that shows up in the R class is generated from the stuff in your project res (aka resources) folder. The R class allows you to reference a resource (such as an image or a string) without having to do file operations all over the place. It does other stuff too, but that's for another answer. Android OS uses a similar scheme - it has a resources folder and the class android.R is the way to access stuff in the android resources folder. The problem arises when in a single class you are using both your own resources, and standard android resources. Normally you can say import at the top, and then reference a class just using the last bit of the name (for example, import java.util.List allows you to just write List in your class and the compiler knows you mean java.util.List). When you need to use two classes that are named the same thing, as is the case with the auto-generated R class, then you can import one of them and you have to fully qualify the other one whenever you want to mean it. Typically I import the R file for my project, and then just say android.R.whatever when I want an android resource.

Also, to reiterate Andy, don't modify the R file automatically. That's not how it's meant to be used.