Android中Fragment相互切换间不被回收的实现方法

前言

Android运行在各种各样的设备中，有小屏幕的手机，超大屏的平板甚至电视。针对屏幕尺寸的差距，很多情况下，都是先针对手机开发一套App，然后拷贝一份，修改布局以适应平板神马超级大屏的。难道无法做到一个App可以同时适应手机和平板么，当然了，必须有啊。Fragment的出现就是为了解决这样的问题。

如今市面上的应用基本上都是单Activity+多Fragment实现的了，而这类APP都有在相互切换时不被回收，即切换回原来的Fragment时还是原先的状态，这就是这里要实现的了。

这里使用Fragment的add() 、show() 、hide()实现，即显示和隐藏，这样原来的Fragment就不会被销毁了。

二话不说，贴代码，代码是最好的老师。

示例代码（注释还算详细了）

public class MainActivity extends AppCompatActivity implements View.OnClickListener { private ImageView ibOne; private ImageView ibTwo; private ImageView ibThree;  private FragmentManager mFm; private ArrayList<Fragment> mFragmentList = new ArrayList<Fragment>(); private String[] mFragmentTagList = {"OneFragment", "TwoFragment", "ThreeFragment"}; private Fragment mCurrentFragmen = null; // 记录当前显示的Fragment @Override protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.activity_main);    initView();  initData();   } private void initData() {  OneFragment oneFragment = new OneFragment();  TwoFragment twoFragment = new TwoFragment();  ThreeFragment threeFragment = new ThreeFragment();  mFragmentList.add(0, oneFragment);  mFragmentList.add(1, twoFragment);  mFragmentList.add(2, threeFragment);  mCurrentFragmen = mFragmentList.get(0);  // 初始化首次进入时的Fragment  mFm = getFragmentManager();  FragmentTransaction transaction = mFm.beginTransaction();  transaction.add(R.id.fl_show, mCurrentFragmen, mFragmentTagList[0]);  transaction.commitAllowingStateLoss(); } // findViewById private void initView() {  ibOne = (ImageView)findViewById(R.id.ib_one);  ibTwo = (ImageView)findViewById(R.id.ib_two);  ibThree = (ImageView)findViewById(R.id.ib_three);  ibOne.setOnClickListener(this);  ibTwo.setOnClickListener(this);  ibThree.setOnClickListener(this); } @Override public void onClick(View view) {  switch (view.getId()){   case R.id.ib_one:    switchFragment(mFragmentList.get(0), mFragmentTagList[0]);    break;   case R.id.ib_two:    switchFragment(mFragmentList.get(1), mFragmentTagList[1]);    break;   case R.id.ib_three:    switchFragment(mFragmentList.get(2), mFragmentTagList[2]);    break;  } } // 转换Fragment void switchFragment(Fragment to, String tag){  if(mCurrentFragmen != to){   FragmentTransaction transaction = mFm.beginTransaction();   if(!to.isAdded()){    // 没有添加过:    // 隐藏当前的，添加新的，显示新的    transaction.hide(mCurrentFragmen).add(R.id.fl_show, to, tag).show(to);   }else{    // 隐藏当前的，显示新的    transaction.hide(mCurrentFragmen).show(to);   }   mCurrentFragmen = to;   transaction.commitAllowingStateLoss();  } } // 当activity非正常销毁时被调用 @Override public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {  super.onSaveInstanceState(outState, outPersistentState);  // 重置Fragment，防止当内存不足时导致Fragment重叠  updateFragment(outState); } // 重置Fragment private void updateFragment(Bundle outState) {  mFm = getFragmentManager();  if(outState == null){   FragmentTransaction transaction = mFm.beginTransaction();   OneFragment oneFragment = new OneFragment();   mCurrentFragmen = oneFragment;   transaction.add(R.id.fl_show, oneFragment, mFragmentTagList[0]).commitAllowingStateLoss();  }else{   // 通过tag找到fragment并重置   OneFragment oneFragment = (OneFragment) mFm.findFragmentByTag(mFragmentTagList[0]);   TwoFragment twoFragment = (TwoFragment) mFm.findFragmentByTag(mFragmentTagList[1]);   ThreeFragment threeFragment = (ThreeFragment) mFm.findFragmentByTag(mFragmentTagList[2]);   mFm.beginTransaction().show(oneFragment).hide(twoFragment).hide(threeFragment);  } }}