View getId is null Android

// Context instead Activity as a parameter
@Override
public void onAttach(Context context) {
    super.onAttach(context);

    Activity a;

    if (context instanceof Activity){
        a=(Activity) context;
    }

}

OnNoteClickedListener listener;
/* old emxample of usage
	@Override
	public void onAttach(Activity activity) {
		super.onAttach(activity);
		try {
			listener = (OnNoteClickedListener) activity;
		} catch (ClassCastException e) {
			throw new ClassCastException(activity.toString()
					+ " must implement OnNoteClickedListener");
		}
	}
*/
// new version of code
	@Override
	public void onAttach(Context context) {
		super.onAttach(context);

		Activity a;

		if (context instanceof Activity){
			a=(Activity) context;
			try {
				listener = (OnNoteClickedListener) a;
			} catch (ClassCastException e) {
				throw new ClassCastException(a.toString()
						+ " must implement OnNoteClickedListener");
			}
		}

	}

Map<Float,String> linkedHashMap = new LinkedHashMap<Float, String>();

 linkedHashMap.put(14.f, "text");
 linkedHashMap.put(13.f, "text");
 linkedHashMap.put(10.f, "text");
 linkedHashMap.put(11.f, "text");
 linkedHashMap.put(2.f, "text");
 linkedHashMap.put(3.f, "text");
 linkedHashMap.put(1.f, "text");
 linkedHashMap.put(7.f, "text");
 linkedHashMap.put(23.f, "text");

	for (Entry<Float,String> entry : linkedHashMap.entrySet()) {
		System.out.println(entry.getKey());
	}
14.0
13.0
10.0
11.0
2.0
3.0
1.0
7.0
23.0

Map<Float,String> hashMap = new HashMap<Float, String>();

 hashMap.put(14.f, "text");
 hashMap.put(13.f, "text");
 hashMap.put(10.f, "text");
 hashMap.put(11.f, "text");
 hashMap.put(2.f, "text");
 hashMap.put(3.f, "text");
 hashMap.put(1.f, "text");
 hashMap.put(7.f, "text");
 hashMap.put(23.f, "text");

 
 
	for (Entry<Float,String> entry : hashMap.entrySet()) {
		System.out.println(entry.getKey());
	}
// key :
1.0
14.0
3.0
13.0
2.0
7.0
11.0
23.0
10.0

public class MainActivity extends Activity {
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(new SampleView(this));
	}


	private static class SampleView extends View {

		// CONSTRUCTOR
		public SampleView(Context context) {
			super(context);
			setFocusable(true);

		}
		@Override
		protected void onDraw(Canvas canvas) {
			Paint paint = new Paint();
			
			canvas.drawColor(Color.YELLOW);
            
          // Bitmap b = Bitmap.createBitmap(200, 200, Bitmap.Config.ARGB_8888);
			
		    //  you need to insert a image flower_blue into res/drawable folder 
			Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.flower_blue);
			 Matrix mat = new Matrix();
			                mat.postRotate(90);
			                Bitmap bmpRotate = Bitmap.createBitmap(bmp, 0, 0,
			  bmp.getWidth(), bmp.getHeight(),
			  mat, true);
		   int h = bmp.getHeight();
           
           canvas.drawBitmap(bmp, 10,10, paint);
           canvas.drawBitmap(bmpRotate, 10,10 + h + 10, paint);
           
		}

	}
}

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        final AssetManager assetManager = getAssets();
        try {
			// for assets folder add empty string
                        String[] filelist = assetManager.list("");
                        // for assets/subFolderInAssets add only subfolder name
                        String[] filelistInSubfolder = assetManager.list("subFolderInAssets");
			if (filelist == null) {
			    // dir does not exist or is not a directory
			} else {
			    for (int i=0; i<filelist.length; i++) {
			        // Get filename of file or directory
			        String filename = filelist[i];
			    }
			}
                     
                        // if(filelistInSubfolder == null) ............  

		} catch (IOException e) {
			e.printStackTrace();
		}
     }