Android พอเพิ่มปุ่ม Button แล้ว เปิด App แล้ว Error Unfortunely

package com.example.paint;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;

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

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

package com.example.paint;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;

public class SingleTouchEventView extends View  {
	private Paint paint = new Paint();
	  private Path path = new Path();
	 Button btn = (Button)findViewById(R.id.button1);
	 //Button btn2 = (Button)findViewById(R.id.button2);
	  public SingleTouchEventView(Context context, AttributeSet attrs) {
	    super(context, attrs);
	    
	    paint.setAntiAlias(true);
	    paint.setStrokeWidth(6f);    
	    paint.setStyle(Paint.Style.STROKE);
	    paint.setStrokeJoin(Paint.Join.ROUND);
	    paint.setColor(Color.BLACK);
	    
			
	   /* btn2.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				paint.setColor(Color.BLACK);
			}
		});*/
	    
	    
	  }

	  @Override
	  protected void onDraw(Canvas canvas) {
	    canvas.drawPath(path, paint);
	    
	  }

	  @Override
	  public boolean onTouchEvent(MotionEvent event) {
	    float eventX = event.getX();
	    float eventY = event.getY();

	    switch (event.getAction()) {
	    case MotionEvent.ACTION_DOWN:
	      path.moveTo(eventX, eventY);
	      return true;
	    case MotionEvent.ACTION_MOVE:
	      path.lineTo(eventX, eventY);
	      break;
	    case MotionEvent.ACTION_UP:
	      // nothing to do
	      break;
	    default:
	      return false;
	    }

	    // Schedules a repaint.
	    invalidate();
	    return true;
	  }

}