首先描述下所要实现的功能点：
MainActivity使用Fragment实现底部菜单，底部共有四个菜单按钮，分别对应：AFragment，BFragment，CFragment，DFragment。其中AFragment是默认显示。
点击CFragment中的一个button后跳转到第二个Activity界面：SecondActivity。
SecondActivity返回键有两个：button01、button02.其中button01返回的是CFragment；button02返回的是AFragment。
问题出现了：
button01可以返回到MainActivity中的CFragment,但是button02却没实现返回到MainActivity中的AFragment,无论是在SecondActivity中使用finish()，还是使用Intent跳转，都不能实现返回到MainActivity中的AFragment。
最后想到了广播机制来实现（我总感觉应该有更简单更好的方法，，却始终没找到，迫不得已使用广播机制）。
去出现了另外一个问题：
Fragment java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState。
最后fragmentTransaction.commitAllowingStateLoss()替换掉fragmentTransaction.commit()解决问题。
最后再浏览下代码：
import java.util.ArrayList;import android.annotation.SuppressLint;import android.app.Activity;import android.app.AlertDialog;import android.app.Dialog;import android.content.BroadcastReceiver;import android.content.Context;import android.content.DialogInterface;import android.content.Intent;import android.content.IntentFilter;import android.graphics.Color;import android.graphics.drawable.Drawable;import android.os.Bundle;import android.support.v4.app.FragmentManager;import android.support.v4.app.FragmentTransaction;import android.view.MotionEvent;import android.view.View;import android.view.View.OnClickListener;import android.widget.ImageButton;import android.widget.TextView;import com.nostra13.universalimageloader.cache.disc.naming.Md5FileNameGenerator;import com.nostra13.universalimageloader.core.ImageLoader;import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;import com.nostra13.universalimageloader.core.assist.QueueProcessingType;public class MainActivity extends BaseActivity {private static final String LOG_TAG = MainActivity.class.getSimpleName();private FragmentManager fragmentManager;private TextView txt_home;private TextView txt_find;private TextView txt_collection;private TextView txt_setting;private FragmentTransaction transaction;private HomeFragment homeFragment;private FindFragment findFragment;private CollectionFragment collectionFragment;private SettingFragment settingFragment;private ImageButton imgbtn_voice;private final static int SCANNIN_GREQUEST_CODE = 65537;private BackBroadcast backBroadcast;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);ResourceHelper.activityContext = this;setContentView(R.layout.activity_main);initImageLoaderConfi();initView();}/** * 底部菜单切换 */private void initView() {fragmentManager = getSupportFragmentManager();txt_home= (TextView) findViewById(R.id.home_text);txt_find= (TextView) findViewById(R.id.find_text);txt_collection = (TextView) findViewById(R.id.collection_text);txt_setting = (TextView) findViewById(R.id.setting_text);txt_home.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {setTabSelection(0);}});txt_find.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {setTabSelection(1);}});txt_collection.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {setTabSelection(2);}});txt_setting.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {setTabSelection(3);}});setTabSelection(0);}@SuppressLint("NewApi")public void setTabSelection(int index) {clearSelection();transaction = fragmentManager.beginTransaction();hideFragments(transaction);switch (index) {case 0:// 当点击了tab时，改变控件的图片和文字颜色Drawable drawable01 = this.getResources().getDrawable(R.drawable.home_home_pressed);txt_home.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawable01, null, null);txt_home.setTextColor(Color.parseColor("#2786c8"));if (homeFragment == null) {homeFragment = new HomeFragment();transaction.add(R.id.content, homeFragment);} else {transaction.show(homeFragment);}break;case 1:Drawable drawable02 = this.getResources().getDrawable(R.drawable.home_find_pressed);txt_find.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawable02, null, null);txt_find.setTextColor(Color.parseColor("#2786c8"));if (findFragment == null) {findFragment = new FindFragment();transaction.add(R.id.content, findFragment);} else {transaction.show(findFragment);}break;case 2:Drawable drawable03 = this.getResources().getDrawable(R.drawable.home_collection_pressed);txt_collection.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawable03, null, null);txt_collection.setTextColor(Color.parseColor("#2786c8"));if (collectionFragment == null) {collectionFragment = new CollectionFragment();transaction.add(R.id.content, collectionFragment);} else {transaction.show(collectionFragment);}break;case 3:Drawable drawable04 = this.getResources().getDrawable(R.drawable.home_setting_pressed);txt_setting.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawable04, null, null);txt_setting.setTextColor(Color.parseColor("#2786c8"));if (settingFragment == null) {settingFragment = new SettingFragment();transaction.add(R.id.content, settingFragment);} else {transaction.show(settingFragment);}break;}transaction.commitAllowingStateLoss(); //该处是重点，如果使用transaction.commit()会一直崩溃报错。}// 每次选中之前先清楚掉上次的选中状态@SuppressLint("NewApi")private void clearSelection() {txt_home.setTextColor(Color.parseColor("#82858b"));Drawable drawableHome = this.getResources().getDrawable(R.drawable.home_home_normal);txt_home.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawableHome, null, null);txt_find.setTextColor(Color.parseColor("#82858b"));Drawable drawableFind = this.getResources().getDrawable(R.drawable.home_find_normal);txt_find.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawableFind, null, null);txt_collection.setTextColor(Color.parseColor("#82858b"));Drawable drawableMy = this.getResources().getDrawable(R.drawable.home_collection_normal);txt_collection.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawableMy, null, null);txt_setting.setTextColor(Color.parseColor("#82858b"));Drawable drawableMore = this.getResources().getDrawable(R.drawable.home_setting_normal);txt_setting.setCompoundDrawablesRelativeWithIntrinsicBounds(null, drawableMore, null, null);}// 先隐藏掉所有的Fragment，以防止有多个Fragment显示在界面上的情况private void hideFragments(FragmentTransaction transaction) {if (homeFragment != null) {transaction.hide(homeFragment);}if (findFragment != null) {transaction.hide(findFragment);}if (collectionFragment != null) {transaction.hide(collectionFragment);}if (settingFragment != null) {transaction.hide(settingFragment);}}@Overrideprotected void onResume() {super.onResume();//setTabSelection(0);backBroadcast = new BackBroadcast();registerReceiver(backBroadcast, new IntentFilter(Constant.HOME_BACK_ACTION));}@Overrideprotected void onDestroy() {super.onDestroy();unregisterReceiver(backBroadcast);}private class BackBroadcast extends BroadcastReceiver{@Overridepublic void onReceive(Context context, Intent intent) {String temp = intent.getAction();if (temp.equals(Constant.HOME_BACK_ACTION)) {setTabSelection(0);}}}@Overrideprotected void onSaveInstanceState(Bundle outState) {super.onSaveInstanceState(outState);}}顺便把布局也贴出来吧：
人生的失败往往是在关键时刻少了坚持。
