addView()出错，怎么回事啊？

package my.test;
import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.widget.LinearLayout;public class TestActivity extends Activity { @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final DrawView dv = new DrawView(this);
LinearLayout  lin =(LinearLayout)this.findViewById(R.layout.main);
//dv.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.MATCH_PARENT));
dv.setMinimumWidth(300);
dv.setMinimumHeight(500); dv.setOnTouchListener(new OnTouchListener(){
public boolean onTouch(View v, MotionEvent event) {
dv.currentX = (event.getX());
dv.currentY = (event.getY());
dv.invalidate();
return true;
}
});
lin.addView(dv);//这里总出错！
}
}