android 中FragmentActivity中模拟返回键返回上一个Activity效果

package com.example.fragmentdemo;

import android.app.Activity;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {
    private FragmentManager mFragmentManager;
    private Fragment1 fragment1;
    private Fragment2 fragment2;
    private Button button1;
    private FragmentTransaction fragmentTransaction;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //新建两个Fragment
        fragment1 = new Fragment1();
        fragment2 = new Fragment2();
        mFragmentManager = getFragmentManager();
        //Fragment事务
        fragmentTransaction = mFragmentManager.beginTransaction();
        //增加执行的动画效果 动画不能用我们的Tween动画，后面会有代码
        fragmentTransaction.setCustomAnimations(R.anim.animation_view, R.anim.animation_view_exit);
        //加入1个Fragment
        fragmentTransaction.add(R.id.myFrameLayout, fragment1);
        fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        fragmentTransaction.commit();
        button1 = (Button)findViewById(R.id.button1);
        button1.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View v) {
                fragmentTransaction = mFragmentManager.beginTransaction();
                //执行动画，显示fragment2
                fragmentTransaction.setCustomAnimations(R.anim.animation_view, R.anim.animation_view_exit);
                if (fragment2.isAdded()) {
                    fragmentTransaction.commit();
                }else{
                    fragmentTransaction.add(R.id.myFrameLayout, fragment2);
                    fragmentTransaction.addToBackStack(null);
                    fragmentTransaction.commit();
                }
            }
        });
        
    }

    @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;
    }
    
    @Override
    protected void onResume() {
        
        super.onResume();
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        mFragmentManager.popBackStack();
        
    }
    
    
}