我是Android开发的新手，我没有太多的SO币。 基本上，我的项目有一个主屏幕活动，它包含3个选项卡，分别是MyGiftsFragment，FriendsGiftsFragment和AboutMeFragment。我在这里实现了tablayout和viewpager。问题是，当我登录应用程序时，第一页（MyGiftsFragment）为空，没有加载任何内容（有时它已加载。）但是当我刷到最后一个选项卡（AboutMeFragment）并返回第一个选项卡时，内容将会加载。这只有在我刷到最后一个标签时才有效。
由于我的英语限制，我不确定我是否清楚地解释了这个问题。如果您需要任何进一步的信息，请发表评论。我搜索了“setUserVisibleHint”和“setOnPageChangeListener（pageChangeListener）”，但似乎它们不是我想要的。任何建议将被认真考虑。非常感谢你。
以下是我的MainScreenActivity代码。
public class MainScreenActivity extends AppCompatActivity {
private static final String TAG = MainScreenActivity.class.getName();
FirebaseAuth mAuth;
private DrawerLayout mDrawerLayout;
private FloatingActionButton fab;
private ArrayList<Gift> mGiftArray;
private RecyclerView mRecyclerView;
private boolean doubleBackToExitPressedOnce = false;
private DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FacebookSdk.sdkInitialize(getApplication().getApplicationContext());
mAuth = FirebaseAuth.getInstance();
setContentView(R.layout.activity_main_screen);
/** Setup Toolbar and ActionBar. */
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
ActionBar actionBar = getSupportActionBar();
actionBar.setHomeAsUpIndicator(R.drawable.ic_menu);
actionBar.setDisplayHomeAsUpEnabled(true);
/** Setup DrawerLayout. */
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
NavigationView navigationView = (NavigationView) findViewById(R.id.navigation_view);
/** 1.Setup drawer header content: Title and profile picture. */
View drawerHeader = navigationView.getHeaderView(0);
NetworkImageView drawerPicture = (NetworkImageView) drawerHeader.findViewById(R.id.drawer_picture);
NetworkImageView coverPicture = (NetworkImageView) drawerHeader.findViewById(R.id.cover_picture);
/** Fetch data from SharePreferences. */
SharedPreferences mSharedPreferences = this.getSharedPreferences("test", Activity.MODE_PRIVATE);
String drawerPictureUrl = mSharedPreferences.getString("picture", "");
String coverPictureUrl = mSharedPreferences.getString("cover", "");
ImageLoader imageLoader = MySingleton.getInstance(MainScreenActivity.this.getApplicationContext()).getImageLoader();
drawerPicture.setImageUrl(drawerPictureUrl, imageLoader);
coverPicture.setImageUrl(coverPictureUrl, imageLoader);
/** 2.Setup drawer body content: Name, E-mail and birthday. */
/** Fetch data from SharePreferences. */
String username = mSharedPreferences.getString("username", "");
String email = mSharedPreferences.getString("email", "");
String birthday = mSharedPreferences.getString("birthday", "");
Menu menu = navigationView.getMenu();
MenuItem nav_name = menu.findItem(R.id.navigation_item_name);
nav_name.setTitle(username);
MenuItem nav_email = menu.findItem(R.id.navigation_item_email);
nav_email.setTitle(email);
MenuItem nav_birthday = menu.findItem(R.id.navigation_item_birthday);
nav_birthday.setTitle(birthday);
/** Setup item onSelectedListener. */
navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
Intent intent;
if (menuItem.getItemId() == R.id.navigation_item_name) {
mDrawerLayout.closeDrawers();
intent = new Intent(MainScreenActivity.this, AddGiftsActivity.class);
startActivity(intent);
return true;
}
if (menuItem.getItemId() == R.id.navigation_item_email) {
mDrawerLayout.closeDrawers();
intent = new Intent(MainScreenActivity.this, AddGiftsActivity.class);
startActivity(intent);
return true;
}
if (menuItem.getItemId() == R.id.navigation_item_birthday) {
mDrawerLayout.closeDrawers();
intent = new Intent(MainScreenActivity.this, AddGiftsActivity.class);
startActivity(intent);
return true;
}
if (menuItem.getItemId() == R.id.navigation_item_payment) {
mDrawerLayout.closeDrawers();
intent = new Intent(MainScreenActivity.this, AddGiftsActivity.class);
startActivity(intent);
return true;
}
if (menuItem.getItemId() == R.id.navigation_item_refresh) {
mDrawerLayout.closeDrawers();
finish();
startActivity(getIntent());
return true;
}
if (menuItem.getItemId() == R.id.navigation_item_logout) {
mDrawerLayout.closeDrawers();
facebookLogout();
return true;
}
return false;
}
});
/** Setup FloatingActionButton. */
fab = (FloatingActionButton)findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Context context = view.getContext();
Intent intent = new Intent(context, AddGiftsActivity.class);
context.startActivity(intent);
}
});
TabPagerAdapter adapter = new TabPagerAdapter(this, getSupportFragmentManager());
final ViewPager viewPager = (ViewPager)findViewById(R.id.viewpager);
viewPager.setAdapter(adapter);
viewPager.setCurrentItem(0);
TabLayout tabLayout = (TabLayout)findViewById(R.id.tablayout);
tabLayout.setupWithViewPager(viewPager);
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
animateFab(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
//
// viewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
// @Override
// public void onPageSelected(int position) {
// // do your work
// }
// });
}
private void animateFab(int position) {
switch (position) {
case 0:
fab.show();
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Context context = view.getContext();
Intent intent = new Intent(context, AddGiftsActivity.class);
context.startActivity(intent);
}
});
break;
case 1:
fab.show();
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Context context = view.getContext();
Intent intent = new Intent(context, AddGiftsActivity.class);
context.startActivity(intent);
}
});
break;
default:
fab.hide();
break;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
switch (id) {
case android.R.id.home:
mDrawerLayout.openDrawer(GravityCompat.START);
return true;
case R.id.action_settings:
return true;
case R.id.action_logout:
facebookLogout();
}
return super.onOptionsItemSelected(item);
}
static class TabPagerAdapter extends FragmentStatePagerAdapter {
private Context mContext;
public TabPagerAdapter(Context context, FragmentManager fm) {
super(fm);
mContext = context;
}
public Fragment getItem(int position) {
if (position == 0) {
return new MyGiftsFragment();
} else if (position == 1) {
return new FriendsGiftsFragment();
} else {
return new AboutMeFragment();
}
}
@Override
public int getCount() {
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
if (position == 0) {
return mContext.getString(R.string.my_gifts);
} else if (position == 1) {
return mContext.getString(R.string.friends_gifts);
} else {
return mContext.getString(R.string.about_me);
}
}
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
moveTaskToBack(false);
return true;
}
return super.onKeyDown(keyCode, event);
}
public void facebookLogout() {
if (mAuth.getCurrentUser() != null) {
Log.e("22", "Not sign out yet.");
} else {
Log.e("22", "Signed out already.");
}
mAuth.signOut();
if (mAuth.getCurrentUser() != null) {
Log.e("22", "Not sign out yet.");
} else {
Log.e("22", "Signed out already.");
}
LoginManager.getInstance().logOut();
Log.e("facebook", "logout");
startActivity(new Intent(MainScreenActivity.this, FacebookLoginActivity.class));
finish();
}
}
这是MyGiftsFragment
public class MyGiftsFragment extends Fragment {
private static final String TAG = MyGiftsFragment.class.getName();
private ArrayList<Gift> mGiftArray;
private RecyclerView mRecyclerView;
private SwipeRefreshLayout mSwipeRefreshLayout;
private DatabaseReference mDatabase;
private String facebookId;
public MyGiftsFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_list_view, container, false);
mRecyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerview);
mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
mGiftArray = new ArrayList<>();
SharedPreferences mSharedPreferences = this.getActivity().getSharedPreferences("test", Activity.MODE_PRIVATE);
facebookId = mSharedPreferences.getString("facebookId", "");
mDatabase = FirebaseDatabase.getInstance().getReference();
DatabaseReference myWishList = mDatabase.child("user/" + facebookId + "/my_gift/" + "/wish_list");
myWishList.addChildEventListener(new ChildEventListener() {
/** Add new gift */
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
mGiftArray.clear();
/** com.jluo80.amazinggifter.MyGiftsFragment:-KMa77KnGU5hsF8dngVc*/
final String uniqueKey = dataSnapshot.getKey();
Log.e(TAG, "onChildAdded:" + uniqueKey);
/** com.jluo80.amazinggifter.MyGiftsFragment:true */
Log.e(TAG, "onChildAdded:" + dataSnapshot.getValue());
DatabaseReference ref = mDatabase.child("gift").child(uniqueKey);
ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot item) {
Log.e(TAG, "Single" + item.getKey());
System.out.println("test" + item.getValue());
Gift gift = item.getValue(Gift.class);
gift.setUnique_key(uniqueKey);
System.out.println(gift.getInitiator_id() + "&&&&&&&" + gift.getReceiver_id());
String end = gift.getDue_date();
String start = getCurrentDate();
if(gift.getProgress() <= gift.getPrice() && end.compareTo(start) >= 0) {
mGiftArray.add(gift);
mRecyclerView.setAdapter(new MyGiftRecyclerAdapter(getContext(), mGiftArray));
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.w(TAG, "getUser:onCancelled", databaseError.toException());
}
});
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
Log.e(TAG, "onChildChanged:" + dataSnapshot.getKey());
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
Log.e(TAG, "onChildRemoved:" + dataSnapshot.getKey());
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
Log.d(TAG, "onChildMoved:" + dataSnapshot.getKey());
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.w(TAG, "postComments:onCancelled", databaseError.toException());
}
});
DatabaseReference fromFriendsList = mDatabase.child("user/" + facebookId + "/my_gift/" + "/from_friends");
fromFriendsList.addChildEventListener(new ChildEventListener() {
/** Add new gift */
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
// mGiftArray.clear();
/** com.jluo80.amazinggifter.MyGiftsFragment:-KMa77KnGU5hsF8dngVc*/
final String uniqueKey = dataSnapshot.getKey();
Log.e(TAG, "onChildAdded:" + uniqueKey);
/** com.jluo80.amazinggifter.MyGiftsFragment:true */
Log.e(TAG, "onChildAdded:" + dataSnapshot.getValue());
DatabaseReference ref = mDatabase.child("gift/" + uniqueKey);
ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot item) {
Log.e(TAG, "Single" + item.getKey());
System.out.println("test" + item.getValue());
Gift gift = item.getValue(Gift.class);
gift.setUnique_key(uniqueKey);
System.out.println(gift.getInitiator_id() + "&&&&&&&" + gift.getReceiver_id());
String end = gift.getDue_date();
String start = getCurrentDate();
if(gift.getProgress() <= gift.getPrice() && end.compareTo(start) >= 0) {
mGiftArray.add(gift);
mRecyclerView.setAdapter(new MyGiftRecyclerAdapter(getContext(), mGiftArray));
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.w(TAG, "getUser:onCancelled", databaseError.toException());
}
});
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
Log.e(TAG, "onChildChanged:" + dataSnapshot.getKey());
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
Log.e(TAG, "onChildRemoved:" + dataSnapshot.getKey());
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
Log.d(TAG, "onChildMoved:" + dataSnapshot.getKey());
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.w(TAG, "postComments:onCancelled", databaseError.toException());
}
});
return rootView;
}
public String getCurrentDate() {
Calendar calendar = Calendar.getInstance();
SimpleDateFormat mdformat = new SimpleDateFormat("MM/dd/yy");
return mdformat.format(calendar.getTime());
}
}
答案 0 :(得分：1)
请在设置适配器之前添加此行。这将解决问题
viewPager.setOffscreenPageLimit(3);
屏幕外页面限制将决定在您看到页面时需要加载多少个相邻页面。因此在您的情况下将其设置为3（所有页面）。
然后您的代码将更改为，
final ViewPager viewPager = (ViewPager)findViewById(R.id.viewpager);
viewPager.setAdapter(adapter);
viewPager.setOffscreenPageLimit(3); //Add this
viewPager.setCurrentItem(0);