Android runtime change switch Activity theme

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        LinearLayout layout = (LinearLayout) findViewById(R.id.layout);
            TextView textView = new TextView(this);
            textView.setText("Text View ");
            LinearLayout.LayoutParams p = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.FILL_PARENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT
            );
            layout.addView(textView, p);

            Button buttonView = new Button(this);
            buttonView.setText("Button");
            buttonView.setOnClickListener(mThisButtonListener);
            layout.addView(buttonView, p);
        
    }
    private OnClickListener mThisButtonListener = new OnClickListener() {
        public void onClick(View v) {
            Toast.makeText(MainActivity.this, "Hello !",
                    Toast.LENGTH_LONG).show();
        }
    };
}

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

			paint.setFilterBitmap(true);
			Bitmap bitmapOrg = BitmapFactory.decodeResource(getResources(),
					R.drawable.flower_blue);
			canvas.drawBitmap(bitmapOrg, 10, 10, paint);
			int width, height;

		    Canvas c = new Canvas(b);
		    paint.setAlpha(255); //0x80
		    c.translate(0, 30);
		    c.drawBitmap(bitmapOrg, new Matrix(), paint);
		    paint.setColor(Color.BLUE);
        Path mPath = new Path();
		    mPath.addCircle(50, 50, 50, Path.Direction.CCW);
            //c.clipPath(mPath, Region.Op.UNION);
            //c.clipPath(mPath, Region.Op.DIFFERENCE);
            c.clipPath(mPath, Region.Op.INTERSECT);
            //c.clipPath(mPath, Region.Op.REPLACE);
            //c.clipPath(mPath, Region.Op.XOR);
           paint.setColor(Color.GREEN);
           paint.setAntiAlias(true);
           c.drawCircle(30, 20, 30, paint);

		    int h = bitmapOrg.getHeight();
			//canvas.drawBitmap(bitmapOrg, 10, 10, paint);
			canvas.drawBitmap(b, 0, 10 + h + 10, paint);

		}

	}
}

// Toast android.widget.Toast.makeText(Context context, CharSequence text, int duration)
// public static Toast makeText (Context context, CharSequence text, int duration) 

Toast.makeText(getApplicationContext(), "Hello world!",
                  Toast.LENGTH_SHORT).show();

// No resource found that matches the given name (at id with value @id/myButton).
 android:id="@id/myButton" // invalid id notation
 android:id="@+id/myButton" // correct


 // No resource found that matches the given name 
// (at icon with value @drawable/icons).
// exist file icons in res/drawable folder?
<application android:icon="@drawable/icons" 

//No resource found that matches the given name 
//(at theme with value @style/MyThem).
<activity android:name=".Main"
                  android:label="@string/app_name"
                  android:theme="@style/MyThem">

// Exist style MyThem  in styles.xml ?  No only MyTheme
<style name="MyTheme" parent="android:Theme">
        <item name="android:windowTitleSize">50px</item>
</style>



// exist file my_background in folder drawable ?
android:background="@drawable/my_background" // 

// no resource found that matches the given name(at "label" with value "@string/app_name")
// have you the string resource defined in res/values/strings.xml ?
<string name="app_name">"My App"</string>