Android RadioGroup.check() onCheckedChanged 回调 3 次 FragmentTransaction.commit() 不会 立即 起作用

昨天遇到了个Android问题，java.lang.IllegalStateException: Fragment already added. backtrace里边没有自己的代码.(好像是fragment重复添加)

问题情境大概，主界面 四个Tab, FragmentTransaction.add() show() commit() 在 onCheckedChangeListener中，来切换四个fragment，有个需要需要在代码中点击radiobutton的地方（programmatically），结果出问题了，每当点击一个radiobutton处理逻辑大概这样，判端这个指定的FragmentManager.getFragmentByTag(),if null,就 FragmentTransaction.add(fragment…);

上代码片段

setOnCheckedChangeListener

radioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {            @Override            public void onCheckedChanged(RadioGroup group, int checkedId) {//                if(checkedId == radioGroup.getCheckedRadioButtonId()){//                    return;//                }                ZLog.d("MainPage setOnCheckedChangeListener now checked " + checkedId + "  last checked " + lastCheckId);                fragmentTransaction = fragmentManager.beginTransaction();                switch (checkedId) {                    case R.id.one:                        hideOtherFragment("one");                        addOrShowFragment("one", firstFragment);                        break;                    case R.id.two:                        hideOtherFragment("two");                        addOrShowFragment("two", secondFragment);                        break;                    case R.id.three:                        hideOtherFragment("three");                        addOrShowFragment("three", thirdFragment);                        break;                    case R.id.four:                        hideOtherFragment("four");                        addOrShowFragment("four", fourthFragment);                        break;                    case R.id.radio_user:                        hideOtherFragment("user");                        addOrShowFragment("user", userFragment);                        break;                }                ZLog.d("radioGroup onCheckedChange");                fragmentTransaction.commit();                fragmentManager.executePendingTransactions(); //重点                currFragment.scrollTop();//在commit前滚动到顶部                markChecked(checkedId);            }        });

radioGroup.check()

touristSubscription1 = RxBroadcast.fromLocalBroadcast(this, touristnotaccess)                .observeOn(AndroidSchedulers.mainThread())                .doOnNext(new Action1<Intent>() {                    @Override                    public void call(Intent intent) {//                        radioGroup.check(R.id.radio_user);//重点                          RadioButton b = (RadioButton) findViewById(R.id.radio_user);                          b.setChecked(true);                    }                })                .doOnError(new Action1<Throwable>() {                    @Override                    public void call(Throwable throwable) {                        throwable.printStackTrace();                    }                })                .subscribe(new Action1<Intent>() {                    @Override                    public void call(Intent intent) {                    }                });

fragmentTransaction

private void addOrShowFragment(String tag, BaseFragment fragment) {        ZLog.d("addOrShowFragment " + fragmentManager.getFragments() + "  tag " + tag + "  isAdd " + fragment.isAdded());        if (fragmentManager.findFragmentByTag(tag) == null) {            fragmentTransaction.add(R.id.fragments_content, fragment, tag);        } else if (!fragment.isAdded()) {            fragmentTransaction.replace(R.id.fragments_content, fragment, tag);        } else {            fragmentTransaction.show(fragment);        }        currFragment = fragment;    }

RadioGroup.check(layoutid) onCheckedChangeListener#onCheckChanged()调用了 3 次(1 原来的radiobutton，2将要的radiobutton， 3将要的radiobutton)
确实调用了三次，stackoverflow上老外看了源码了，调用了三次。问题在于，第三次调用的时候，判断 将要显示的fragment是否存在于FragmentManager.getFragments()中，明摆着第二次已经add了，已经commit了，FragmentManager.getFragments()还没有，原来commit()不会立即产生效果。解决方式，radiobutton.setChecked(true）替代。

FragmentTransaction.commit()不会立即产生效果。解决方式，FragmentManager.executePendingTransactions(); 立即产生效果

两种解决方式任选其一即可，都选也没事。

Reference (stackoverflow)

• radiogroup-calls-oncheckchanged-three-times

• oncreateview-isnt-called-immediately-after-fragmenttransaction-commit