android Fragment相关问题

1.fragment的切换
以前做项目时，fragment切换总是用replace方法，这样对性能影响很大，所以换一种方式用hide和show方法进行展示。
首先定义一个全局的currentFragment

“`
private Fragment currentFragment = new Fragment();
private FragmentTransaction switchFragment(Fragment targetFragment) {
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
if(!targetFragment.isAdded()){

            if(currentFragment != null){                transaction.hide(currentFragment);            }            transaction.add(R.id.ll_main,targetFragment,targetFragment.getClass().getName());        }else{            transaction.hide(currentFragment).show(targetFragment);        }        currentFragment = targetFragment;    return transaction;}

“
然后再在切换button上直接调用即可
switchFragment(oneFg).commit();
如果想要刷新数据的话，可以利用fragment的隐藏方法:
@Override
public void onHiddenChanged(boolean hidden) {
super.onHiddenChanged(hidden);

    if(hidden){ //隐藏    }else{      //显示    }}

2.fragment重叠
hide和show容易出现fragment重叠现象
解决方法:
通过重写宿主activity的onSaveInstanceState 方法，然后不保存状态
@Override
protected void onSaveInstanceState(Bundle outState) {
// super.onSaveInstanceState(outState);
}
3.getActivity为空
解决方法：
Activity activity;
@Override
public void onAttach(Context context) {
super.onAttach(context);
activity = (Activity) context;
}
4.fragment嵌套
fragment嵌套经常出现崩溃
解决方法:
宿主fragment 使用getChildFragmentManager()；
在宿主fragment中:
@Override
public void onDetach() {
super.onDetach();
try {
//参数是固定写法
Field childFragmentManager = Fragment.class.getDeclaredField(“mChildFragmentManager”);
childFragmentManager.setAccessible(true);
childFragmentManager.set(this, null);
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}

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