[펌] Android Support Library 를 안정감 있게 사용하는 3가지 방법.

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 출처

  : http://aroundck.tistory.com/2897

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출처 : http://www.crashlytics.com/blog/3-key-ways-to-increase-android-support-library-stability/

1. AsyncTasks and Configuration Changes

AsyncTask 를 실행시킨 fragment 가 asyntask 완료 되는 시점에서 activity 로부터 detach 되어있으면 다음과 같은 에러가 발생한다. AsyncTask 가 activity 로부터 detach 되어 있는 상황은 보통 configuration change ( 대표적으로 화면 전환 ) 의 경우에 주로 발생한다.

java.lang.IllegalStateException: Fragment MyFragment not attached to Activity

 at android.support.v4.app.Fragment.getResources(Fragment.java:551)

 at android.support.v4.app.Fragment.getString(Fragment.java:573)

이 에러를 막기 위한 한 방법으로는 AsyncTask 를 configuration change 에 대해 유지되도록 하는 것.

RetainedFragment 라는 class 를 이용하면 listener 를 통해 AsyncTask 의 상태를 listen 할 수 있다.

RetainedFragment 는 Build in class 가 아니고, thread 를 이용해서 config change 에 대해 destory 되지 않도록 하는 custom fragment 로 소스는 아래와 같다.

https://android.googlesource.com/platform/development/+/master/samples/ApiDemos/src/com/example/android/apis/app/FragmentRetainInstance.java

/*  * Copyright (C) 2010 The Android Open Source Project  *  * Licensed under the Apache License, Version 2.0 (the "License");  * you may not use this file except in compliance with the License.  * You may obtain a copy of the License at  *  *      http://www.apache.org/licenses/LICENSE-2.0  *  * Unless required by applicable law or agreed to in writing, software  * distributed under the License is distributed on an "AS IS" BASIS,  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  * See the License for the specific language governing permissions and  * limitations under the License.  */ package com.example.android.apis.app; import com.example.android.apis.R; import android.app.Activity; import android.app.Fragment; import android.app.FragmentManager; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.ProgressBar; /**  * This example shows how you can use a Fragment to easily propagate state  * (such as threads) across activity instances when an activity needs to be  * restarted due to, for example, a configuration change.  This is a lot  * easier than using the raw Activity.onRetainNonConfiguratinInstance() API.  */ public class FragmentRetainInstance extends Activity {     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);                  // First time init, create the UI.         if (savedInstanceState == null) {             getFragmentManager().beginTransaction().add(android.R.id.content,                     new UiFragment()).commit();         }     }     /**      * This is a fragment showing UI that will be updated from work done      * in the retained fragment.      */     public static class UiFragment extends Fragment {         RetainedFragment mWorkFragment;         @Override         public View onCreateView(LayoutInflater inflater, ViewGroup container,                 Bundle savedInstanceState) {             View v = inflater.inflate(R.layout.fragment_retain_instance, container, false);             // Watch for button clicks.             Button button = (Button)v.findViewById(R.id.restart);             button.setOnClickListener(new onClickListener() {                 public void onClick(View v) {                     mWorkFragment.restart();                 }             });             return v;         }         @Override         public void onActivityCreated(Bundle savedInstanceState) {             super.onActivityCreated(savedInstanceState);             FragmentManager fm = getFragmentManager();             // Check to see if we have retained the worker fragment.             mWorkFragment = (RetainedFragment)fm.findFragmentByTag("work");             // If not retained (or first time running), we need to create it.             if (mWorkFragment == null) {                 mWorkFragment = new RetainedFragment();                 // Tell it who it is working with.                 mWorkFragment.setTargetFragment(this, 0);                 fm.beginTransaction().add(mWorkFragment, "work").commit();             }         }     }     /**      * This is the Fragment implementation that will be retained across      * activity instances.  It represents some ongoing work, here a thread      * we have that sits around incrementing a progress indicator.      */     public static class RetainedFragment extends Fragment {         ProgressBar mProgressBar;         int mPosition;         boolean mReady = false;         boolean mQuiting = false;         /**          * This is the thread that will do our work.  It sits in a loop running          * the progress up until it has reached the top, then stops and waits.          */         final Thread mThread = new Thread() {             @Override             public void run() {                 // We'll figure the real value out later.                 int max = 10000;                 // This thread runs almost forever.                 while (true) {                     // Update our shared state with the UI.                     synchronized (this) {                         // Our thread is stopped if the UI is not ready                         // or it has completed its work.                         while (!mReady || mPosition >= max) {                             if (mQuiting) {                                 return;                             }                             try {                                 wait();                             } catch (InterruptedException e) {                             }                         }                         // Now update the progress.  Note it is important that                         // we touch the progress bar with the lock held, so it                         // doesn't disappear on us.                         mPosition++;                         max = mProgressBar.getMax();                         mProgressBar.setProgress(mPosition);                     }                     // Normally we would be doing some work, but put a kludge                     // here to pretend like we are.                     synchronized (this) {                         try {                             wait(50);                         } catch (InterruptedException e) {                         }                     }                 }             }         };         /**          * Fragment initialization.  We way we want to be retained and          * start our thread.          */         @Override         public void onCreate(Bundle savedInstanceState) {             super.onCreate(savedInstanceState);                          // Tell the framework to try to keep this fragment around             // during a configuration change.             setRetainInstance(true);                          // Start up the worker thread.             mThread.start();         }         /**          * This is called when the Fragment's Activity is ready to go, after          * its content view has been installed; it is called both after          * the initial fragment creation and after the fragment is re-attached          * to a new activity.          */         @Override         public void onActivityCreated(Bundle savedInstanceState) {             super.onActivityCreated(savedInstanceState);                          // Retrieve the progress bar from the target's view hierarchy.             mProgressBar = (ProgressBar)getTargetFragment().getView().findViewById(                     R.id.progress_horizontal);                          // We are ready for our thread to go.             synchronized (mThread) {                 mReady = true;                 mThread.notify();             }         }         /**          * This is called when the fragment is going away.  It is NOT called          * when the fragment is being propagated between activity instances.          */         @Override         public void onDestroy() {             // Make the thread go away.             synchronized (mThread) {                 mReady = false;                 mQuiting = true;                 mThread.notify();             }                          super.onDestroy();         }         /**          * This is called right before the fragment is detached from its          * current activity instance.          */         @Override         public void onDetach() {             // This fragment is being detached from its activity.  We need             // to make sure its thread is not going to touch any activity             // state after returning from this function.             synchronized (mThread) {                 mProgressBar = null;                 mReady = false;                 mThread.notify();             }                          super.onDetach();         }         /**          * API for our UI to restart the progress thread.          */         public void restart() {             synchronized (mThread) {                 mPosition = 0;                 mThread.notify();             }         }     } }

2. Safely Performing Fragment Transactions.

Activity 가 fragment transaction 을 handle 할 수 없을 때 transaction 이 발생하면 다음과 같은 에러가 발생한다.

java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState

 at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1327)

 at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager:1338)

 at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:595)

 at android.support.v4.app.BackStackRecord.commit(BackStackRecord:574)

 at android.support.v4.app.DialogFragment.show(DialogFragment:127)

FragmentActivity 가 background 가 되고, FragmentManigerImpl 의 mStateSaved flag 가 true 되었을 때 발생한다.

이 문제를 해결하기 위해서는 onSaveInstanceState() 가 불린 후에는 fragment transaction 이 수행되면 안 된다.

위와 같은 에러는 mStateSaved flag 가 false 로 바뀌기 전에 onResume 이 불릴 경우에 발생한다.

따라서 onResume() 에서의 fragment transaction 을 피하고, onResumeFragment() 에서 수행하는 것이 좋다.

3. Managing the Cursor Lifecycle.

CursorAdapter 를 쓰다 보면 다음과 같은 에러에 봉착하곤 한다.

java.lang.IllegalStateException: this should only be called when the cursor is valid

 at android.support.v4.widget.CursorAdapter.getView(CursorAdapter.java:245)

 at android.widget.HeaderViewListAdapter.getView(HeaderViewListAdapter.java:253)

이는 CursorAdapter 의 mDataValid 가 false 로 되었을 때 발생하며, 이는

1. cursor 가 null 일 경우

2. cursor의 requery 가 끝난 경우.

3. data 에 onInvalidated 가 호출된 경우.

위의 경우에 발생한다.

CursorLoader 와 startManagingCursor() 를 동시에 사용할 경우에 위의 경우가 주로 발생한다.

CursorLoader 가 생기면서 startManagingCursor 는 deprecated 되었다.

따라서 Fragment 와 CursorLoader 를 사용할 경우에는 startManaingCursor(), stopManagingCursor() 모두를 제거해주는 것이 좋다.