问来自以编程方式创建的按钮的Android catch onclick事件

EN

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.Button;


public class MainActivity extends Activity implements View.OnClickListener {

int wrapContent = LinearLayout.LayoutParams.WRAP_CONTENT;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    LinearLayout linLayout = new LinearLayout(this);

    linLayout.setOrientation(LinearLayout.VERTICAL);

    LinearLayout.LayoutParams linLayoutParam = new 
    LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 
    LinearLayout.LayoutParams.MATCH_PARENT);
    setContentView(linLayout, linLayoutParam);


        LinearLayout.LayoutParams lpView = new 
        LinearLayout.LayoutParams(wrapContent, wrapContent);

            Button btn = new Button(this);
            btn.setText("Button");
            linLayout.addView(btn, lpView);

}//fin de onCreate


@Override
public void onClick(View view) {

    switch (view.getId()) {

        case R.id.btn:  //Here the problem begins with error 'btn'

            break;


    }

   }
}