Android选项菜单：页面跳转与setContentView应用

package com.example.w0502;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
    private View v1,v2,v3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
v1=getLayoutInflater().inflate(R.layout.one, null);
v2=getLayoutInflater().inflate(R.layout.second, null);
v3=getLayoutInflater().inflate(R.layout.three, null);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
//super.onCreateOptionsMenu(menu);//调用父类方法加入系统菜单；
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item){
switch(item.getItemId())
{