How can resolve R in Android?

I was run the program to guess random number but in case R, their should be "R cannot be resolved to a variable" error comes many time . And i am also try to import android.R; but could not work without errorless. error comes in to "main" or "R.layout.main". so please fix the problem.

public class GuessGame extends Activity {
    Button btnGuess;
   private EditText enter;
   private GuessGame mcontext;
   private Double guess;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    final Random rand= new Random();
    final int numberToGuess= rand.nextInt(20);
    int numberOfTries=0;

        final boolean win= false;
        btnGuess= (Button)findViewById(R.id.btnGuess);
        enter= (EditText)findViewById(R.id.EnterNumber);

        TextView tv= (TextView) findViewById(R.id.dislpayResult);
        guess=new Double(enter.getText().toString());


     btnGuess.setOnClickListener(new OnClickListener() {
         private AlertDialog show;
         @Override
            public void onClick(View v) {
             while(win == false){
                 if((enter.getText().length() == 0) || (enter.getText().toString() == "")){

                     show= new AlertDialog.Builder(mcontext).setTitle("Error Was Found")
                        .setMessage("Input are Emppty")
                        .setPositiveButton("Ok", null).show();
            }
            else if(guess == numberToGuess){
                //win = true;
                Toast.makeText(GuessGame.this, "You have win", Toast.LENGTH_SHORT).show();
            }
            else if(guess < numberToGuess){
                Toast.makeText(GuessGame.this, "You guess is to low", Toast.LENGTH_SHORT).show();
            }
            else if(guess > numberToGuess){
                Toast t=Toast.makeText(GuessGame.this, "You guess is to high", Toast.LENGTH_SHORT);
                t.show();
            }
          }
        }
    });
    tv.setText("You win");
    tv.setText("Yhe Number was" + numberToGuess);
    tv.setText("Tries times" + numberOfTries);
   }

}

Edited:

Tricks to solve this problem:

Once you have changed all the names of your resources, just clean the project ( Project>Clean..), wait a few seconds, and your R.java file will come back home. Getting the R.java file back should get rid of most of your errors, but if it didn’t, check all your class’ imports for the “import android.R” and if it is there, delete it and clean the project.

More details Solution go to : Details Solution about this article

回答1:

The R.java file should be automatically generated by Android. Try the following:

If you are using Eclipse try "project clean" to regenerate the file.
Try to fix all errors not related to the R file and then retry the "project clean" option. Other errors (e.g. your xml layout files) can "stall" a new build of the R file via project clean.
Make sure your project is an Android project and you have an android.jar file on your classpath.

回答2:

You might not have android minimum SDK version properly configured.

Please check what Android version you have added in your project and what AVD version you have created.

If you have added AVD for API level 7 [Android 2.1] then cross check if it is matching with project.properties file entry as: