privatevoidinitFragment(){mRecommendFragment=newRecommendFragment();mInvestFragment=newInvestFragment();mCla***oomFragment=newCla***oomFragment();mMineFragment=newMineFragment();mBaseFragments=newBaseFragment[]{mRecommendFragment,mInvestFragment,mCla***oomFragment,mMineFragment};}@OverridepublicvoidonClick(Viewv){//TODOAuto-generatedmethodstubswitch(v.getId()){caseR.id.llrecommend:btStatuas(mRecommendFragment,0);switchContent(mRecommendFragment);if(mRecommendFragment.getActivity()!=null){mRecommendFragment.NetFragment();}break;caseR.id.llinvest:btStatuas(mInvestFragment,1);switchContent(mInvestFragment);break;caseR.id.llcla***oom:btStatuas(mCla***oomFragment,2);switchContent(mCla***oomFragment);break;caseR.id.llmine:if(MyApplication.getInstance().getLoginInfo()!=null){btStatuas(mMineFragment,3);switchContent(mMineFragment);if(mMineFragment.getActivity()!=null){mMineFragment.refreshTitleData();}}else{Intentintent=newIntent(MainActivity.this,LoginActivity.class);intent.putExtra("fromact",Constant.FROM_ACT_MAIN);startActivityForResult(intent,0);}break;}}@OverrideprotectedvoidonActivityResult(intrequestCode,intresultCode,Intentdata){//TODOAuto-generatedmethodstubsuper.onActivityResult(requestCode,resultCode,data);switch(resultCode){case1:if(MyApplication.getInstance().getLoginInfo()==null){btStatuas(mCurrentContent,mCurrentLockIndex);switchContent(mCurrentContent);}else{btStatuas(mMineFragment,3);switchContent(mMineFragment);}break;case2:if(MyApplication.getInstance().getLoginInfo()==null){btStatuas(mRecommendFragment,0);switchContent(mRecommendFragment);}break;}}publicvoidswitchContent(Fragmentto){if(mContent!=null&&mContent!=to){FragmentTransactiontransaction=fragmentManager.beginTransaction().setCustomAnimations(android.R.anim.fade_in,android.R.anim.fade_out);if(!to.isAdded()){//先判断是否被add过transaction.hide(mContent).add(R.id.llfrag,to).commitAllowingStateLoss();//隐藏当前的fragment，add下一个到Activity中}else{transaction.hide(mContent).show(to).commitAllowingStateLoss();//隐藏当前的fragment，显示下一个}mContent=to;}}

1、上面代码是多个fragment之间进行切换显示，未添加到activity中的需要add、commit，已添加的需要hide，show。

在FragmentActivity启动时，会加载在Fragment1，当Fragment1--->Activity2----->Activity3---->FragmentActivity(Fragment1)---->Fragment2，时此时Fragmnet属于未被Add入FragmentActivity中，仅仅通过new创建了实例，内部生命周期不跑，其中getActivity == null,isAdded() == false;commit并没有立即执行，而是走正常生命周期，所以不能再activity中不能调用fragment内部方法，ui未加载都为空，不能进行ui刷新。当add过后commit执行完，内部方法可以调用。

2、关于show，hiden时fragment在别的activity中fc后返回会出现fragment显示show异常

protectedvoidonCreate(BundlesavedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);if(savedInstanceState==null){initView();initClick();initFragment();initFragmentContent();//版本检测//initData();}else{initView();initClick();initFragment();fragmentManager=getSupportFragmentManager();FragmentTransactionbeginTransaction=fragmentManager.beginTransaction();btStatuas(mRecommendFragment,0);//findViewById(R.id.llfrag)beginTransaction.replace(R.id.llfrag,mRecommendFragment);//beginTransaction.add(R.id.llfrag,mRecommendFragment);mContent=mBaseFragments[0];beginTransaction.commitAllowingStateLoss();//Toast.makeText(MainActivity.this,"",Toast.LENGTH_SHORT).show();}@OverrideprotectedvoidonSaveInstanceState(BundleoutState){//TODOAuto-generatedmethodstubsuper.onSaveInstanceState(outState);outState.putInt("index",0);}

onSaveInstanceState(Bundle outState)保存状态，当异常重新加载会走onCreate方法，通过保存状态的参数来判断