title: Cannot resolve symbol 'activity_main.xml'
body: <p>I was following  <a href="https://github.com/Ajay191191/Opencv-Face-Recognition" rel="nofollow noreferrer">https://github.com/Ajay191191/Opencv-Face-Recognition</a></p>
  
  <p>The image below shows the error  where at activity_main.xml and below two red circles with the same error.
  <a href="https://i.stack.imgur.com/EBift.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EBift.png" alt="enter image description here"></a></p>
  
  <p>The code is:</p>
  
  <pre><code>package com.example.altaf.opencv_test;
  
  
  import android.content.Intent;
  import java.io.BufferedWriter;
   import java.io.File;
   import java.io.FileInputStream;
   import java.io.FileOutputStream;
   import java.io.FileWriter;
   import java.io.IOException;
   import java.io.InputStream;
   import java.io.ObjectInputStream;
   import java.io.ObjectOutputStream;
   import java.io.OutputStream;
   import java.util.HashMap;
   import java.util.Map;
  import android.support.v7.app.AppCompatActivity;
   import org.opencv.objdetect.CascadeClassifier;
  
   import android.app.Activity;
   import android.content.Intent;
   import android.graphics.Bitmap;
   import android.graphics.BitmapFactory;
   import android.os.Bundle;
   import android.os.Environment;
   import android.util.Log;
  import  android.R;
   import android.view.Menu;
   import android.view.View;
   import android.widget.Button;
   import android.widget.ImageView;
   import android.widget.TextView;
   import android.widget.Toast;
  
   public class MainActivity extends Activity {
  
       Button detect_face, add_name, take_picture;
       TextView tv;
       TextView detectedName;
       private String File_Image_TAG = new String("image_db");
       private String File_Name_TAG = new String("name_db");
       public static Map&lt;Integer, String&gt; idToImage;
       public static Map&lt;Integer, String&gt; idToName;
       public static String current_name = new String("temp");
       ImageView captured_image;
       public static boolean face_detected;
       public static File working_Dir = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/opencv");
       public CascadeClassifier haar_cascade;
       public static int ID;
       private String Name_obt;
       BufferedWriter bW;
       static File fileC;
  
       static {
           working_Dir.mkdirs();
           fileC = new File(MainActivity.working_Dir, "csv.txt");
  
       }
  
       public static boolean pictureTaken, recognized;
  
       //Preview preview;
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
  
           setContentView(R.layout.activity_main);
  
           Name_obt = getIntent().getStringExtra("Name");
           if (Name_obt != null) {
               Log.i("Ajay", "Detected Name" + Name_obt);
           }
  
  
           ButtonListener listener = new ButtonListener();
           detect_face = ((Button) findViewById(R.id.detect_face));
           detect_face.setOnClickListener(listener);
  
           take_picture = (Button) findViewById(R.id.take_picture);
           take_picture.setOnClickListener(listener);
  
           //Load from file:
           File imagefile = new File(working_Dir, File_Image_TAG);
           File nameFile = new File(working_Dir, File_Name_TAG);
           if (imagefile.exists()) {
               try {
                   FileInputStream f = new FileInputStream(imagefile);
                   ObjectInputStream s = new ObjectInputStream(f);
                   idToImage = (Map&lt;Integer, String&gt;) s.readObject();
                   MainActivity.ID = idToImage.size();
  
                   s.close();
                   Log.i("Ajay", "Database Exists");
               } catch (Exception e) {
                   e.printStackTrace();
               }
           }
           if (nameFile.exists()) {
               try {
                   FileInputStream f = new FileInputStream(nameFile);
                   ObjectInputStream s = new ObjectInputStream(f);
                   idToName = (Map&lt;Integer, String&gt;) s.readObject();
  
                   s.close();
                   Log.i("Ajay", "Database Exists");
               } catch (Exception e) {
                   e.printStackTrace();
               }
           }
  
  
           add_name = (Button) findViewById(R.id.Add_n);
           add_name.setOnClickListener(listener);
  
           tv = (TextView) findViewById(R.id.name);
           tv.setVisibility(View.GONE);
  
           detectedName = (TextView) findViewById(R.id.Detected_name);
           detectedName.setVisibility(View.GONE);
  
           captured_image = (ImageView) findViewById(R.id.captured_image);
           if (!pictureTaken) {
               captured_image.setVisibility(View.GONE);
               add_name.setVisibility(View.GONE);
               detect_face.setVisibility(View.GONE);
               take_picture.setVisibility(View.VISIBLE);
           } else {
               if (face_detected) {
                   if (!recognized) {
                       detect_face.setVisibility(View.GONE);
                       add_name.setVisibility(View.VISIBLE);
                       take_picture.setVisibility(View.GONE);
                   } else {
                       //                 TODO: Print the hash value for ID obtained.
                       detectedName.setVisibility(View.VISIBLE);
                       detectedName.setText(Name_obt != null ? Name_obt : "");
                   }
               } else
                   detect_face.setVisibility(View.VISIBLE);
               captured_image.setVisibility(View.VISIBLE);
  
  
               //         add_name.setVisibility(View.GONE);
               take_picture.setVisibility(View.GONE);
               Bitmap bmp = null;
               File f = new File(working_Dir, current_name + "_det.jpg");
               if (f.exists()) {
                   MainActivity.face_detected = true;
                   bmp = BitmapFactory.decodeFile(working_Dir.getAbsolutePath() + "/" + current_name + "_det.jpg");
               } else {
                   MainActivity.face_detected = false;
                   bmp = BitmapFactory.decodeFile(working_Dir.getAbsolutePath() + "/" + current_name + ".jpg");
               }
               captured_image.setImageBitmap(bmp);
           }
       }
  
       @Override
       public boolean onCreateOptionsMenu(Menu menu) {
           getMenuInflater().inflate(R.menu.activity_main, menu);
           return true;
       }
  
       private class ButtonListener implements View.OnClickListener {
           Intent i;
  
           public void onClick(View v) {
  
               if (v.equals(findViewById(R.id.detect_face))) {
                   new Sample3View(getApplicationContext()).FindFaces(working_Dir.getAbsolutePath() + "/" + current_name, Sample3View.mCascadeFile.getAbsolutePath().toString());
                   Log.d("Ajay", "Image dir:" + working_Dir.getAbsolutePath() + "/" + current_name);
                   File f = new File(MainActivity.working_Dir, "csv.txt");
                   int return_id = -1;
                   if (f.exists() &amp;&amp; MainActivity.ID &gt; 1)
                       return_id = new Sample3View(getApplicationContext()).Find(working_Dir.getAbsolutePath() + "/" + current_name, Sample3View.mCascadeFile.getAbsolutePath().toString(), working_Dir.getAbsolutePath() + "/csv.txt");
                   MainActivity.face_detected = true;
                   String Name = null;
                   if (return_id != -1) {
                       Name = new String(idToName.get(return_id));
                       MainActivity.recognized = true;
                   }
                   startActivity(getIntent().putExtra("Name", Name));
                   //TODO : Add Face Detection
               } else if (v.equals(findViewById(R.id.Add_Name))) {
                   tv.setVisibility(View.VISIBLE);
                   if (tv.getText().toString().equals(""))
                       return;
                   String new_name = new String(tv.getText().toString());
                   //             faces.put(current_name, new ArrayList&lt;String&gt;());
                   if (idToImage == null) {
                       idToImage = new HashMap&lt;Integer, String&gt;();
                       MainActivity.ID = 0;
                   }
                   if (idToName == null)
                       idToName = new HashMap&lt;Integer, String&gt;();
  
                   idToImage.put(MainActivity.ID, MainActivity.working_Dir + "/" + new_name + ".jpg");
                   idToImage.put(MainActivity.ID, MainActivity.working_Dir + "/" + new_name + "1.jpg");
                   idToName.put(MainActivity.ID, new_name);
  
  
                   File f = new File(MainActivity.working_Dir, MainActivity.current_name + "_det.jpg");
                   if (!f.exists()) {
                       try {
                           f.createNewFile();
                       } catch (IOException e) {
                           e.printStackTrace();
                       }
                   }
  
                   File f_new = new File(MainActivity.working_Dir, new_name + ".jpg");
                   if (!f_new.exists()) {
                       try {
                           f_new.createNewFile();
                       } catch (IOException e) {
                           e.printStackTrace();
                       }
                   }
                   Log.i("Ajay", MainActivity.working_Dir + "");
                   f.renameTo(f_new);
                   f = new File(MainActivity.working_Dir, new_name + "1.jpg");
  
                   //copy the file content in bytes
                   try {
                       InputStream inStream = new FileInputStream(f_new);
                       OutputStream outStream = new FileOutputStream(f);
  
                       byte[] buffer = new byte[1024];
  
                       int length;
  
                       while ((length = inStream.read(buffer)) &gt; 0) {
  
                           outStream.write(buffer, 0, length);
  
                       }
                       inStream.close();
                       outStream.close();
                   } catch (Exception e) {
                       e.printStackTrace();
                   }
  
  
                   try {
                       File file = new File(MainActivity.working_Dir, File_Image_TAG);
                       FileOutputStream fo = new FileOutputStream(file);
                       ObjectOutputStream s = new ObjectOutputStream(fo);
                       s.writeObject(idToImage);
                       s.close();
                   } catch (Exception e) {
                       e.printStackTrace();
                   }
                   try {
                       File file = new File(MainActivity.working_Dir, File_Name_TAG);
                       FileOutputStream fo = new FileOutputStream(file);
                       ObjectOutputStream s = new ObjectOutputStream(fo);
                       s.writeObject(idToName);
                       s.close();
                   } catch (Exception e) {
                       e.printStackTrace();
                   }
                   try {
                       try {
                           bW = new BufferedWriter(new FileWriter(fileC, true));
                       } catch (IOException e) {
                           // TODO Auto-generated catch block
                           e.printStackTrace();
                       }
                       bW.append(MainActivity.working_Dir + "/" + new_name + ".jpg" + ";" + MainActivity.ID);
                       bW.newLine();
                       bW.append(MainActivity.working_Dir + "/" + new_name + "1.jpg" + ";" + MainActivity.ID);
                       bW.newLine();
                       bW.close();
                   } catch (Exception e) {
                       e.printStackTrace();
                   }
  
  
                   Toast.makeText(getApplicationContext(), "Name Added", Toast.LENGTH_SHORT).show();
                   MainActivity.ID++;
                   startActivity(getIntent());
                   MainActivity.face_detected = false;
                   MainActivity.pictureTaken = false;
                   MainActivity.recognized = false;
                   //             Log.i("Ajay","String : " + current_name);
               } else if (v.equals(findViewById(R.id.take_picture))) {
                   i = new Intent(MainActivity.this, Sample3Native.class);
                   startActivity(i);
               }
           }
       }
   }
  </code></pre>