Cannot resolve symbol R

[Josh Diamond]

Building my first android game and am getting "cannot resolve symbol R" (lines 31-39) on several java files for instance my EnemyShip class. Using Android Studio ver 2.3.3. I have enemy ship png's in my resources folder so don't really know why I'm getting this error.

package com.gamecodeschool.tappydefender;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Rect;

import java.util.Random;

public class EnemyShip{
    private Bitmap bitmap;
    private int x, y;
    private int speed = 1;

    // Detect mines leaving the screen
    private int maxX;
    private int minX;
    // Spawn mines within screen bounds
    private int maxY;
    private int minY;

    // A hit box for collision detection
    private Rect hitBox;

    // Constructor
    public EnemyShip(Context context, int screenX, int screenY){
        Random generator = new Random();
        int whichBitmap = generator.nextInt(3);
        switch (whichBitmap){
            case 0:
                bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.enemy3);
                break;

            case 1:
                bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.enemy2);
                break;

            case 2:
                bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.enemy);
                break;


        }

        scaleBitmap(screenX);

        maxX = screenX;
        maxY = screenY;
        minX = 0;
        minY = 0;


        speed = generator.nextInt(6)+10;

        x = screenX;
        y = generator.nextInt(maxY) - bitmap.getHeight();

        // Initialize the hit box
        hitBox = new Rect(x, y, bitmap.getWidth(), bitmap.getHeight());

    }

    public void update(int playerSpeed) {
        x -= playerSpeed;
        x -= speed;

        //respawn when off screen
        if (x < minX - bitmap.getWidth()) {
            Random generator = new Random();
            speed = generator.nextInt(10) + 10;
            x = maxX;
            y = generator.nextInt(maxY) - bitmap.getHeight();
        }

        // Refresh hit box location
        hitBox.left = x;
        hitBox.top = y;
        hitBox.right = x + bitmap.getWidth();
        hitBox.bottom = y + bitmap.getHeight();
    }

    //Getters and Setters
    public Bitmap getBitmap(){

        return bitmap;
    }
    public int getX() {

        return x;
    }

    public int getY() {

        return y;
    }

    public Rect getHitbox(){
        return hitBox;
    }


    // This is used by the TDView update() method to
    // Make an enemy out of bounds and force a re-spawn
    public void setX(int x) {
        this.x = x;
    }

    public void scaleBitmap(int x){

        if(x < 1000) {
            bitmap = Bitmap.createScaledBitmap(bitmap,
                bitmap.getWidth() / 3,
                bitmap.getHeight() / 3,
                false);
        }else if(x < 1200){
            bitmap = Bitmap.createScaledBitmap(bitmap,
                bitmap.getWidth() / 2,
                bitmap.getHeight() / 2,
                false);
        }
    }

}

[Ron McLeod]

R is a generated class.  You may need to manually import it in to your code.

The R class should be in the top-level package for application.  For example, in my case the top-level package for the application is: com.mcleodnet.hflink, so my code imports: import com.mcleodnet.hflink.R

package com.mcleodnet.hflink.ui;

... 

import com.mcleodnet.hflink.R;

...

public class MainActivity extends Activity implements UIMessageReceiver,
		StationDialogListener, ChannelDialogListener {

	...
        channelMenuItem.setIcon(R.drawable.ic_action_channel_green);

}

[Norm Radder]

The IDE takes care of building the R.java file.  Often an error in an XML file will cause the IDE not to generate the R.java file.  Check all the xml files for errors.

[Josh Diamond]

Getting errors in my XML files lines 3-9 e.g. cannot resolve symbol @dimen/activity_horizontal_margin

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    android:paddingBottom="@dimen/activity_vertical_margin"    tools:context="com.gamecodeschool.c1tappydefender.GameActivity">    <TextView android:text="@string/hello_world" android:layout_width="wrap_content"        android:layout_height="wrap_content" /> </RelativeLayout>

Also getting errors here from lines 3-6 e.g. line 3 cannot resolve symbol @dimen/activity_horizontal_margin
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">    <TextView android:text="High Score: 9999" android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/textHiScore"        android:layout_alignParentTop="true"        android:layout_alignParentRight="true"        android:layout_alignParentEnd="true" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Play"        android:id="@+id/buttonPlay"        android:layout_alignParentBottom="true"        android:layout_alignParentRight="true"        android:layout_alignParentEnd="true"        android:layout_marginRight="127dp"        android:layout_marginEnd="127dp"        android:layout_marginBottom="78dp" /> </RelativeLayout>

[Norm Radder]

cannot resolve symbol @dimen/activity_horizontal_margin

That value should be defined in the dimens.xml file in the res/values folder.