在导航抽屉片段中保留状态

Question

我有一个导航抽屉项目，我只是使用 Android Studio 从“创建新项目 > 导航抽屉”中修改它。导航抽屉中有几个“菜单”，每个菜单都会打开不同的片段。问题是每次我使用抽屉导航时，都会重新创建片段。意思是当用户对一个fragment做了一些改动，之后当用户再次访问fragment时，这些改动就丢失了。我用过 setRetainInstance(true);但这似乎只适用于方向改变。

这是我用来显示所选片段的代码的一部分：

private void selectItem(int position) {
        mCurrentSelectedPosition = position;
        if (mDrawerListView != null) {
            mDrawerListView.setItemChecked(position, true);
        }
        if (mDrawerLayout != null) {
            mDrawerLayout.closeDrawer(mFragmentContainerView);
        }
        if (mCallbacks != null) {
            mCallbacks.onNavigationDrawerItemSelected(position);
        }

        Fragment fragment = null;
        FragmentTransaction transaction = getFragmentManager().beginTransaction();
        FragmentManager fm = getFragmentManager();

        switch (position) {
            case 0:
                fragment = fm.findFragmentByTag("fragmentDashboard");
                if (fragment == null){
                    fragment = new Dashboard();
                    transaction.replace(R.id.container, fragment, "fragmentDashboard");
                    transaction.addToBackStack(null);
                    transaction.commit();
                }else{
                    transaction.remove(getFragmentManager().findFragmentByTag("fragmentDashboard"));
                    transaction.commit();
                    fm.popBackStack();
                }

                break;
            case 1:
                fragment = fm.findFragmentByTag("fragmentExpenses");
                if (fragment == null) {
                    fragment = new Expenses();
                    transaction.replace(R.id.container, fragment, "fragmentExpenses");
                    transaction.addToBackStack(null);
                    transaction.commit();
                }else{
                    transaction.remove(getFragmentManager().findFragmentByTag("fragmentExpenses"));
                    transaction.commit();
                    fm.popBackStack();
                }

                break;


            default:
                break;
        }
    }

编辑：这个问题Save fragment state with navigation drawer 是我解决问题的最接近的解决方案，但答案太简短了......而且我在 android 开发方面还很陌生。那么有人可以帮忙吗？

Answer 1

试试这个代码 :: 而不是replacing-fragments .... 每次Hide 和Show 的片段

说明::

• 而不是destroying the fragments .... 创建fragment 为 第一次和每隔一次find the fragment and use it, instead of replacing it

---

代替代码 ::

   private void selectItem(int position) {
            mCurrentSelectedPosition = position;
            if (mDrawerListView != null) {
                mDrawerListView.setItemChecked(position, true);
            }
            if (mDrawerLayout != null) {
                mDrawerLayout.closeDrawer(mFragmentContainerView);
            }
            if (mCallbacks != null) {
                mCallbacks.onNavigationDrawerItemSelected(position);
            }

            Fragment fragment = null;
            FragmentTransaction transaction = getFragmentManager().beginTransaction();
            FragmentManager fm = getFragmentManager();

            switch (position) {
                case 0:
                    fragment = fm.findFragmentByTag("fragmentDashboard");
                    if (fragment == null){
                        fragment = new Dashboard();
                        transaction.replace(R.id.container, fragment, "fragmentDashboard");
                        transaction.addToBackStack(null);
                        transaction.commit();
                    }else{
                        transaction.remove(getFragmentManager().findFragmentByTag("fragmentDashboard"));
                        transaction.commit();
                        fm.popBackStack();
                    }

                    break;
                case 1:
                    fragment = fm.findFragmentByTag("fragmentExpenses");
                    if (fragment == null) {
                        fragment = new Expenses();
                        transaction.replace(R.id.container, fragment, "fragmentExpenses");
                        transaction.addToBackStack(null);
                        transaction.commit();
                    }else{
                        transaction.remove(getFragmentManager().findFragmentByTag("fragmentExpenses"));
                        transaction.commit();
                        fm.popBackStack();
                    }

                    break;


                default:
                    break;
            }
        }

---

使用这个：

   private void selectItem(int position) {
            mCurrentSelectedPosition = position;
            if (mDrawerListView != null) {
                mDrawerListView.setItemChecked(position, true);
            }
            if (mDrawerLayout != null) {
                mDrawerLayout.closeDrawer(mFragmentContainerView);
            }
            if (mCallbacks != null) {
                mCallbacks.onNavigationDrawerItemSelected(position);
            }

            Fragment fragment = null;
            FragmentTransaction transaction = getFragmentManager().beginTransaction();
            FragmentManager fm = getFragmentManager();

            switch (position) {
                case 0:
                    fragment = fm.findFragmentByTag("fragmentDashboard");
                    if (fragment == null){
                        fragment = new Dashboard();
                        transaction.add(R.id.container, fragment, "fragmentDashboard");
                        transaction.addToBackStack(null);
                        transaction.commit();
                    }else{
                        transaction.show(getFragmentManager().findFragmentByTag("fragmentDashboard"));
                        transaction.commit();
                        fm.popBackStack();
                    }

                    break;
                case 1:
                    fragment = fm.findFragmentByTag("fragmentExpenses");
                    if (fragment == null) {
                        fragment = new Expenses();
                        transaction.add(R.id.container, fragment, "fragmentExpenses");
                        transaction.addToBackStack(null);
                        transaction.commit();
                    }else{
                        transaction.show(getFragmentManager().findFragmentByTag("fragmentExpenses"));
                        transaction.commit();
                        fm.popBackStack();
                    }

                    break;


                default:
                    break;
            }
        }

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