【发布时间】：2017-05-06 17:02:15
【问题描述】：
在我的应用程序中，我有两个片段：FragmentA 和 FragmentB，它们是在 SlidingMenu 的帮助下从我的MainActivity 加载的。
当显示FragmentB 时，它会立即在后台启动AsyncTask 以从服务器加载数据。加载过程由活动的SwipeRefreshLayout 反映给用户。
加载完成后，FragmentB 的 UI 会在传递给 MyAsyncClass 的委托的帮助下使用加载的数据进行刷新。
我现在面临以下问题：
只要调用了我的委托中的processFinish，我就会在swipeRefreshLayout.setRefreshing(false) 的帮助下停止SwipeRefreshLayout 的刷新。
如果用户在后台任务仍在进行时返回FragmentA，则在大约 20% 的情况下，FragmentB 仍处于用户界面中FragmentA 的背景中（请参见下面的屏幕截图） .
正如您在图片中看到的那样，显示了FragmentA（文本“尚未播放曲目”来自FragmentA），但在背景中您仍然可以看到FragmentB。
如前所述，这并非 100% 的情况，因此不应该是背景/透明度问题。如果我注释掉swipeRefreshLayout.setRefreshing(false)，那么问题是不可重现的，但不知何故我需要停止SwipeRefreshLayout，以防用户留在FragmentB。
知道导致这种行为的原因吗？
异步响应接口：
public interface AsyncResponse {
void processFinish(String result);
}
FragmentB 类：
public class FragmentB extends MyFragment implements SwipeRefreshLayout.OnRefreshListener, AsyncResponse {
private SwipeRefreshLayout swipeRefreshLayout;
private View view;
private RecyclerView recyclerView;
public FragmentB () {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.songs_list, container, false);
swipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.swipe_refresh_layout);
swipeRefreshLayout.setOnRefreshListener(this);
swipeRefreshLayout.setColorSchemeColors(getResources().getColor(R.color.colorPrimary));
// Set the adapter
Context context = view.getContext();
recyclerView = (RecyclerView) view.findViewById(R.id.listinclude);
recyclerView.setLayoutManager(new LinearLayoutManager(context));
recyclerView.addItemDecoration(new DividerItemDecoration(getActivity(), R.drawable.divider));
List<Song> songsList = databaseHandler.getAllSongs();
setVisibilities(songsList);
this.recyclerViewAdapter = new RecyclerViewAdapter(songsList, mListener, false, false);
recyclerView.setAdapter(this.recyclerViewAdapter);
swipeRefreshLayout.setRefreshing(true);
receive();
return view;
}
private void setVisibilities(List<Song> songsList) {
ViewFlipper viewFlipper = (ViewFlipper) view.findViewById(R.id.viewFlipper);
if (songsList.isEmpty() && viewFlipper.getDisplayedChild() == 0) {
viewFlipper.setDisplayedChild(1);
} else if (!songsList.isEmpty() && viewFlipper.getDisplayedChild() == 1) {
viewFlipper.setDisplayedChild(0);
}
}
@Override
public void onRefresh() {
if (MyOnlineHelper.isOnline(getContext())) {
receive();
} else {
swipeRefreshLayout.setRefreshing(false);
}
}
private void receive() {
new MyAsyncClass(this, getContext()).execute("receiving");
}
@Override
public void processFinish(String output) {
// refreshUI
swipeRefreshLayout.setRefreshing(false);
}
}
FragmentA 类：
public class FragmentA extends MyFragment implements AsyncResponse {
private View view;
private RecyclerView recyclerView;
public FragmentA() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
List<Song> songsList = myDatabaseHandler.getAllSongs();
view = inflater.inflate(R.layout.home_list, container, false);
// Set the adapter
Context context = view.getContext();
recyclerView = (RecyclerView) view.findViewById(R.id.listinclude);
recyclerView.setLayoutManager(new LinearLayoutManager(context));
recyclerView.addItemDecoration(new DividerItemDecoration(getActivity(), R.drawable.divider));
setVisibilities(songsList);
this.recyclerViewAdapter = new RecyclerViewAdapter(songsList, mListener, false, true);
recyclerView.setAdapter(this.recyclerViewAdapter);
return view;
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
}
private void setVisibilities(List<Song> songsList) {
ViewFlipper viewFlipper = (ViewFlipper) view.findViewById(R.id.viewFlipper);
if (songsList.isEmpty() && viewFlipper.getDisplayedChild() == 0) {
viewFlipper.setDisplayedChild(1);
} else if (!songsList.isEmpty() && viewFlipper.getDisplayedChild() == 1) {
viewFlipper.setDisplayedChild(0);
}
}
@Override
public void processFinish(String output) {
// does something
}
}
MyAsyncClass：
public class MyAsyncClass extends AsyncTask<String, Integer, String> {
private AsyncResponse delegate;
private Context mContext;
private MyDatabaseHandler myDatabaseHandler;
public MyAsyncClass(AsyncResponse delegate, Context context) {
this.delegate = delegate;
this.mContext = context;
}
@Override
protected String doInBackground(String... params) {
// calling webservice and writing it to the database
}
@Override
protected void onPostExecute(String result) {
delegate.processFinish(result);
super.onPostExecute(result);
}
}
MainActivity-类：
public class MainActivity extends AppCompatActivity implements MyFragment.OnListFragmentInteractionListener, AsyncResponse {
private FragmentA fragmentA = new FragmentA();
private FragmentB fragmentB;
private NavigationView navigationView;
private DrawerLayout drawer;
private Toolbar toolbar;
// index to identify current nav menu item
private static int navItemIndex = 0;
public static String CURRENT_TAG = MyConstants.TAG_FRAGMENT_A;
// toolbar titles respected to selected nav menu item
private String[] activityTitles;
// flag to load home fragment when user presses back key
private Handler mHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentA.setDatabaseHandler(this.myDatabaseHandler);
// Init UI
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mHandler = new Handler();
drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
navigationView = (NavigationView) findViewById(R.id.nav_view);
fabSendButton = (FloatingActionButton) findViewById(R.id.fab);
// Navigation view header
navHeader = navigationView.getHeaderView(0);
// load toolbar titles from string resources
activityTitles = getResources().getStringArray(R.array.sliding_menu_item_activity_titles);
// initializing navigation menu
setUpNavigationView();
if (savedInstanceState == null) {
navItemIndex = 0;
CURRENT_TAG = MyConstants.TAG_FRAGMENT_A;
loadHomeFragment();
}
}
/***
* Returns respected fragment that user
* selected from navigation menu
*/
private void loadHomeFragment() {
// set toolbar title
setToolbarTitle();
// if user select the current navigation menu again, don't do anything
// just close the navigation drawer
if (getSupportFragmentManager().findFragmentByTag(CURRENT_TAG) != null) {
drawer.closeDrawers();
return;
}
// Sometimes, when fragment has huge data, screen seems hanging
// when switching between navigation menus
// So using runnable, the fragment is loaded with cross fade effect
// This effect can be seen in GMail app
Runnable mPendingRunnable = new Runnable() {
@Override
public void run() {
// update the activity_main_header_with_item content by replacing fragments
Fragment fragment = getFragment();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out);
fragmentTransaction.replace(R.id.frame, fragment, CURRENT_TAG);
fragmentTransaction.commit();
}
};
// If mPendingRunnable is not null, then add to the message queue
if (mPendingRunnable != null) {
mHandler.post(mPendingRunnable);
}
//Closing drawer on item click
drawer.closeDrawers();
// refresh toolbar menu
invalidateOptionsMenu();
}
private Fragment getFragment() {
switch (navItemIndex) {
case 0:
return this.fragmentA;
case 1:
if (fragmentB == null) {
fragmentB = new FragmentB();
fragmentB.setDatabaseHandler(this.myDatabaseHandler);
}
return fragmentB;
default:
return this.fragmentA;
}
}
private void setToolbarTitle() {
getSupportActionBar().setTitle(activityTitles[navItemIndex]);
}
private void setUpNavigationView() {
//Setting Navigation View Item Selected Listener to handle the item click of the navigation menu
navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
// This method will trigger on item Click of navigation menu
@Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
//Check to see which item was being clicked and perform appropriate action
switch (menuItem.getItemId()) {
//Replacing the activity_main_header_with_item content with ContentFragment Which is our Inbox View;
case R.id.nav_A:
navItemIndex = 0;
CURRENT_TAG = MyConstants.TAG_FRAGMENT_A;
break;
case R.id.nav_B:
navItemIndex = 1;
CURRENT_TAG = MyConstants.TAG_FRAGMENT_B;
break;
default:
navItemIndex = 0;
}
loadHomeFragment();
return true;
}
});
ActionBarDrawerToggle actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.openDrawer, R.string.closeDrawer) {
@Override
public void onDrawerClosed(View drawerView) {
// Code here will be triggered once the drawer closes as we dont want anything to happen so we leave this blank
super.onDrawerClosed(drawerView);
}
@Override
public void onDrawerOpened(View drawerView) {
// Code here will be triggered once the drawer open as we dont want anything to happen so we leave this blank
super.onDrawerOpened(drawerView);
}
};
//Setting the actionbarToggle to drawer layout
drawer.setDrawerListener(actionBarDrawerToggle);
//calling sync state is necessary or else your hamburger icon wont show up
actionBarDrawerToggle.syncState();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main_header_with_item, menu);
return true;
}
}
【问题讨论】：
标签： android multithreading android-fragments android-asynctask swiperefreshlayout