Android, "R's" red throughout the code

I have a code which I tried to compile for the first time, and when I was about to compile it sent me two errors:

  

Error: java.lang.RuntimeException: Some file crunching failed, see logs   for details

     

Error: Execution failed for task ': app: mergeDebugResources'.

     

Error: java.lang.RuntimeException: Some file crunching failed, see logs for details

This is my code:

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    ImageView img;
    Button immg;
    private final int PICKER = 1;
    String encodedImage,foto,funcion;
    DataConnctcion dc;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        img = (ImageView)findViewById(R.id.imageView2);
        immg = (Button) findViewById(R.id.button);
        immg.setOnClickListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_send) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onClick(View v) {
        PickFile();
    }
    private void PickFile(){
        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.setType("image/*");
        try {
            startActivityForResult(
                    Intent.createChooser(intent, "Instale un administrador de archivos."), PICKER);
        }catch (android.content.ActivityNotFoundException ex){

        }
    }
    protected void onActivityResult(int requestCode, int sesultCode, Intent data){
        switch (requestCode){
            case PICKER:
                if (requestCode == RESULT_OK){
                    foto = "foto";
                    Bitmap photobmp;
                    Uri selectdImageUri = data.getData();
                    String dataFU = getRealPathFromURI(selectdImageUri);
                    photobmp = BitmapFactory.decodeFile(dataFU);
                    img.setImageBitmap(photobmp);

                    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                                           photobmp.compress(Bitmap.CompressFormat.JPEG,88,baos);
                    byte[] imageBytes = baos.toByteArray();
                                            encodedImage = Base64.encodeToString(imageBytes, Base64.DEFAULT);
                }
                break;
        }
    }
    public String getRealPathFromURI(Uri contentUri){
        Cursor cursor = null;
        try {
            String[] proj = {MediaStore.Images.Media.DATA};
            cursor = getApplicationContext().getContentResolver().query(contentUri, proj, null, null, null);
            int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
            cursor.moveToFirst();
            return cursor.getString(column_index);
        }finally {
            if (cursor != null){
                cursor.close();
            }
        }
    }
}

Can you tell me why these errors occur and how can I solve them?