setContentView()后对Button设置的监听无效了,该怎么处理

package lab.sodino.layoutdemo;

import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;

public class LayoutDemoAct extends Activity implements OnClickListener {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // Set up click listeners for all the buttons
        View linearView = findViewById(R.id.linearBtn);
        linearView.setOnClickListener(this);
        View tableView = findViewById(R.id.tableBtn);
        tableView.setOnClickListener(this);
        View frameView = findViewById(R.id.frameBtn);
        frameView.setOnClickListener(this);
        View absoluteView = findViewById(R.id.absoluteBtn);
        absoluteView.setOnClickListener(this);
        View relativeView = findViewById(R.id.relativeBtn);
        relativeView.setOnClickListener(this);
    }

    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu, menu);
        Log.d("Sodino", "Inflate menu item");
        return true;
    }

    public void onClick(View v) {
        //点击按钮进入不同的布局界面
        if (v.getId() == R.id.linearBtn) {
            //进入linearLayout界面
            setContentView(R.layout.linearlayoutdemo);
        } else if (v.getId() == R.id.tableBtn) {
            setContentView(R.layout.tablelayoutdemo);
        } else if (v.getId() == R.id.frameBtn) {
            setContentView(R.layout.framelayoutdemo);
        } else if (v.getId() == R.id.absoluteBtn) {
            setContentView(R.layout.absolutelayoutdemo);
        } else if (v.getId() == R.id.relativeBtn) {
            setContentView(R.layout.relativelayoutdemo);
        }
    }

    public boolean onOptionsItemSelected(MenuItem item) {
//        super.onOptionsItemSelected(item);
        if (item.getItemId() == R.id.backMenu) {
            setContentView(R.layout.main);
            //返回 主界面 后，如果没有再次设置监听
            //则再次返回主界面时点击相应的按钮无效
            View linearView = findViewById(R.id.linearBtn);
            linearView.setOnClickListener(this);
            View tableView = findViewById(R.id.tableBtn);
            tableView.setOnClickListener(this);
            View frameView = findViewById(R.id.frameBtn);
            frameView.setOnClickListener(this);
            View absoluteView = findViewById(R.id.absoluteBtn);
            absoluteView.setOnClickListener(this);
            View relativeView = findViewById(R.id.relativeBtn);
            relativeView.setOnClickListener(this);
            return true;
        }
        return false;
    }
}