popbackstackimmediate illegalstateexception片段已添加

Question

我正在玩下面的代码 我有3个frags和3个按钮 我在按下每个按钮时调用此方法。

当我按照以下顺序崩溃时，FragmentA已经添加了错误 A-＆GT; B-＆GT; C-＆GT; A-＆GT; B-＆GT; C-＆GT; A-> B（崩溃popBackStackImmediate时崩溃）

我无法理解为什么会崩溃:(

protected void setContent(@IdRes int containerResId, @NonNull Class<? extends Fragment> fragment, Bundle extras) {
        final String tag = fragment.getName();
        Log.i("PLAYFRAGTAG","-----------------------------------------------------------------------------");
        Fragment frg = fragmentManager.findFragmentByTag(tag);
        Fragment frgA = fragmentManager.findFragmentByTag("com.playfrag.FragmentA");
        Fragment frgB = fragmentManager.findFragmentByTag("com.playfrag.FragmentB");
        Fragment frgC = fragmentManager.findFragmentByTag("com.playfrag.FragmentC");


        Log.i("PLAYFRAGTAG","stat : A "+(frgA!=null?frgA.isAdded():"null") +" B "+(frgB!=null?frgB.isAdded():"null")+" C "+(frgC!=null?frgC.isAdded():"null"));

        boolean addToBackStack = (frg == null);
        boolean fragmentPopped = false;
        if (frg == null) {
            try {
                frg = fragment.newInstance();
                // loadExtras(frg, extras);
            } catch (InstantiationException e) {
                Log.e("Exception  " + tag, e.toString());
            } catch (IllegalAccessException e) {
                Log.e("IllegalAccessException" + tag, e.toString());
            }
        } else {
            //loadExtras(frg, extras);
            fragmentPopped = fragmentManager.popBackStackImmediate(tag, 0);
        }
        if (frg == null) {
            throw new IllegalArgumentException("Fragment could not be instantiated.");
        }
        Log.i("PLAYFRAGTAG","popd : "+fragmentPopped);
        if (fragmentPopped) {
            return;
        }

        addToBackStack = addToBackStack && (fragmentManager.getFragments() != null && (fragmentManager.getFragments().size() > 0));
        FragmentTransaction ft = fragmentManager.beginTransaction();

        Log.i("PLAYFRAGTAG","stat : A "+(frgA!=null?frgA.isAdded():"null") +" B "+(frgB!=null?frgB.isAdded():"null")+" C "+(frgC!=null?frgC.isAdded():"null"));

        Log.i("PLAYFRAGTAG","-----------------------------------------------------------------------------");

        if (!frg.isAdded()) {
            ft.replace(containerResId, frg, tag);
        } else if (frg.isDetached()) {
            ft.attach(frg);
        }
        if (addToBackStack) {
            ft.addToBackStack(tag);
        }
        ft.commitAllowingStateLoss();
    }