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。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);
}
}
}
我以前对于这种需求是在一个Activity中使用RelativeLayout，在其中加入多个布局（类似Fragment），当点击下方Tab时设置布局的visibility的，思想是一样的，但这样实现起来很是丑陋，所以不建议使用。
如果有更好的实现方案希望您可以告诉我哦～
