带有 TabLayout 的 Android ViewPager 片段意外地起作用

Question

我的第一个主要应用程序再次造成严重破坏。 我的主要活动上有一个 tabLayout，用于在 3 个片段之间轻松切换。这是他们的标签

-“IP信息”

-“网络扫描”

-“实用程序”...

自从我 3 个月前开始这项活动以来，我的片段就出现了奇怪的行为。最大的问题是，首次启动活动时，我的片段中没有任何内容出现。这是一个空白页。我必须切换到另一个活动，然后一次或多次返回主要活动才能显示我的内容。对我来说，空白片段的实例似乎不规则，我无法追踪为它抛出的可靠错误。

这是我的整个主要活动，如果有什么事情发生的话：

public class MainActivity extends AppCompatActivity
    implements devicesFragment.OnListFragmentInteractionListener,
                IPInfoFragment.OnFragmentInteractionListener,
                ToolsSelectionFragment.OnFragmentInteractionListener
{
public SectionsPagerAdapter mSectionsPagerAdapter;
public ViewPager mViewPager;

private SharedPreferences myprefs;
private SharedPreferences.Editor editor;
private final String PREFS_NAME = "userPrefs";

private MyDevice mydev;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    mydev = new MyDevice(this);
    new MyDeviceWorker().execute();
    myprefs = getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
    editor = myprefs.edit();

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    // Create the adapter that will return a fragment fors each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.container);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(mViewPager);
}


public void setActionBarTitle(String title){
    getSupportActionBar().setTitle(title);
}

//region ACTIONBAR
@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_main2, 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();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        //clear shared-preferences
        editor.clear();
        Intent logoutIntent = new Intent(MainActivity.this, LoginActivity.class);
        finish();
        startActivity(logoutIntent);
    }

    if (id == R.id.action_profile) {
        Intent intent = new Intent(this, ProfileActivity.class);
        startActivity(intent);
    }

    return super.onOptionsItemSelected(item);
}

@Override
public void onListFragmentInteraction(Devices device) {
}
//endregion

//region ASYNCTASK_RUNNERS
private class MyDeviceWorker extends AsyncTask {

    @Override
    protected Object doInBackground(Object[] params) {

        mydev.setListNetworkInterfaces();
        mydev.setInterfacesByDisplayName();
        mydev.getSSIDName();
        mydev.getLocalAddresses("wlan0");

        return this;
    }
}
//endregion
@Override
public void onFragmentInteraction(String title) {

}

@Override
public void onFragmentInteraction(Uri uri) {

}
//endregion

//region PAGE ADAPTER
public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class below).
        switch (position) {
            case 0:
                Parcelable wrapped = Parcels.wrap(mydev);
                return IPInfoFragment.newInstance(position + 1, wrapped);
            case 1:
                return devicesFragment.newInstance(position);
            case 2:
                return ToolsSelectionFragment.newInstance(position + 1);
            default:
                Parcelable wrappeddefault = Parcels.wrap(mydev);
                return IPInfoFragment.newInstance(position + 1, wrappeddefault);
        }
    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 3;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        switch (position) {
            case 0:
                return getText(R.string.title_fragment_IPINFO);
            case 1:
                return getText(R.string.title_fragment_NETSCAN);
            case 2:
                return getText(R.string.title_fragment_UTILITIES);
        }
        return null;
    }
}
//endregion
} 

方法：public Fragment getItem(int position) {} 是片段的膨胀。

和我的片段示例都类似地膨胀：

public ToolsSelectionFragment() {
    // Required empty public constructor
}

public static ToolsSelectionFragment newInstance(int sectionNumber) {
    ToolsSelectionFragment fragment = new ToolsSelectionFragment();
    Bundle args = new Bundle();
    args.putInt(ARG_SECTION_NUMBER, sectionNumber);
    fragment.setArguments(args);
    return fragment;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.fragment_tools_selection,container, false);
    initvar(v);
    registerButtonListeners();
    return v;
}

如果格式关闭，我们深表歉意。只是希望有人对我的问题有意见。

*********更新********* 由于缺乏解析，这是我的片段的完整代码

IPInfo 片段：

public class IPInfoFragment extends Fragment implements Serializable, myResultReceiver.Receiver  {


//region UI VARS
TextView tvStatus;
TextView tvPrivateIP;
TextView tvPrivateMAC;
TextView tvConnectionStatus;
TextView tvSSID;
TextView tvNetMask;
TextView tvFrequency;
TextView tvSignal;
TextView tvBroadcast;
TextView tvBSSID;
TextView tvNetIP;
//endregion

public myResultReceiver mReceiver;
public DatabaseHelper dbhelper;

public static String PrivateIP;
public static String PrivateMAC;
public MyDevice mydev;
public Network mynet;
public MyNet personalNet;
public User currentUser;


public final String PREFS_NAME = "userPrefs";
public SharedPreferences myprefs;
public SharedPreferences.Editor editor;



//region FRAGMENT STUFF
private OnFragmentInteractionListener mListener;
private static final String ARG_SECTION_NUMBER = "section_number";
private static final String MYDEV_KEY = "MyDevices_Key";

public IPInfoFragment() {
    // Required empty public constructor
}

/**
 * Returns a new instance of this fragment for the given section
 * number.
 */
public static IPInfoFragment newInstance(int sectionNumber, Parcelable wrappedDev) {
    IPInfoFragment fragment = new IPInfoFragment();
    Bundle args = new Bundle();
    args.putInt(ARG_SECTION_NUMBER, sectionNumber);
    args.putParcelable(MYDEV_KEY, wrappedDev);

    fragment.setArguments(args);
    return fragment;
}


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) 

    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.fragment_ipinfo, container, false);
    ((MainActivity) getActivity()).setActionBarTitle("IP Info");


    //keep track of current user
    myprefs = getActivity().getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
    currentUser = new User(myprefs.getString("USERNAME_KEY", "---"), myprefs.getString("EMAIL_KEY", "---"), myprefs.getString("USERPASS_KEY", "---"));


    mydev = Parcels.unwrap(getArguments().getParcelable(MYDEV_KEY));
    new MyDeviceWorker().execute();

    launchNetworkSniffer(1);
    ViewPager mViewPager = (ViewPager) v.findViewById(R.id.container);


    PrivateIP = mydev.getIp();
    PrivateMAC = mydev.getMac();

    initVar(v);

    return v;
}


public void launchNetworkSniffer(int opr) {
    Intent serviceIntent = new Intent(getActivity(), NetHelper.class);

    //setup resultReceiver for service callbacks
    mReceiver = new myResultReceiver(new android.os.Handler());
    mReceiver.setReceiver(this);


    serviceIntent.putExtra(NetHelper.BUNDLE_RECEIVER2, mReceiver);
    serviceIntent.putExtra("OPR", opr);
    getActivity().startService(serviceIntent);
}


@Override
public void onAttach(Context context) {
    super.onAttach(context);
    if (context instanceof OnFragmentInteractionListener) {
        mListener = (OnFragmentInteractionListener) context; }

}

@Override
public void onDetach() {
    super.onDetach();
    mListener = null;
}

//region ASYNCTASK_RUNNERS
private class MyDeviceWorker extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... params) {
        Log.d("BACKGROUND_STARTED", "doing background stufffss**********(^*%fsdf");

        mydev.setListNetworkInterfaces();
        mydev.setInterfacesByDisplayName();
        mydev.getSSIDName();
        mydev.getLocalAddresses("wlan0");

        return null;
    }

    @Override
    protected void onPostExecute(Void v) {

        tvPrivateIP.setText(mydev.getIp().toString());
        tvPrivateMAC.setText(mydev.getMac().toString());
    }

}
//endregion


@Override
public void onReceiveResult(int resultCode, Bundle resultData) {
    Log.d("NET_DATA_RECEIVED", "processing...");

    String newnetjson = resultData.getString("DATA_");
    Log.d("DATA_", newnetjson);

    Gson gson = new Gson();
    mynet = gson.fromJson(newnetjson, Network.class);

    //region DATABASE WORK
    //confusing naming conventions but whatever, It's crunch time.
    personalNet = new MyNet(currentUser.getName(), mynet.getSSID(), mynet.getBSSID(), mynet.getSignal(), mynet.getFrequency(), mynet.getNetIP(), mynet.getBroadcast(), mynet.getNetMask());

    new Thread(new Runnable() {
        @Override
        public void run() {
            dbhelper = new DatabaseHelper(getActivity().getApplicationContext());

            //if returns true, a record exists - so just update teh times connected counter
            if (dbhelper.checkNetworkHistory(currentUser.getName(), mynet.getSSID())) {
                Log.d("DB_IPINFO_OP", "updating user history record for this network");
                dbhelper.updateNetCounter(personalNet);
            }
            else {
                Log.d("DB_IPINFO_OP", "adding new network to user history");
                dbhelper.addUserNetwork(personalNet);
            }

        }
    }).start();



    //region FILL UI
    if (mynet.getState()) { tvConnectionStatus.setText("Connected."); }
    else { tvConnectionStatus.setText("Disconnected"); }

    tvSSID.setText(mynet.getSSID());
    tvBroadcast.setText(mynet.getBroadcast());

    if (mynet.getFrequency() == 0) { tvFrequency.setText("----"); }
    else { tvFrequency.setText(String.valueOf(mynet.getFrequency())); }

    tvBSSID.setText(mynet.getBSSID());

    tvNetIP.setText(mynet.getNetIP());

    if (mynet.getNetMask() == 0)  { tvNetMask.setText("----"); }
    else { tvNetMask.setText(String.valueOf(mynet.getNetMask())); }

    if (mynet.getSignal() == 0) { tvSignal.setText("----"); }
    else { tvSignal.setText(String.valueOf(mynet.getSignal())); }
    //endregion
}

public interface OnFragmentInteractionListener {
    // TODO: Update argument type and name
    void onFragmentInteraction(String title);
}
//endregion


public void initVar(View v) {
    tvPrivateIP = (TextView) v.findViewById(R.id.tvPersonalIP);
    tvPrivateMAC = (TextView) v.findViewById(R.id.tvPersonalMAC);
    tvConnectionStatus = (TextView) v.findViewById(R.id.lblisConnected);
    tvSSID = (TextView) v.findViewById(R.id.tvSSID);
    tvBSSID = (TextView) v.findViewById(R.id.tvBSSID);
    tvNetMask = (TextView) v.findViewById(R.id.tvNetMask);
    tvFrequency = (TextView) v.findViewById(R.id.tvFrequency);
    tvSignal = (TextView) v.findViewById(R.id.tvSignal);
    tvBroadcast = (TextView) v.findViewById(R.id.tvBroadCast);
    tvNetIP = (TextView) v.findViewById(R.id.tvNetIP);

    tvPrivateIP.setText(PrivateIP);
    tvPrivateMAC.setText(PrivateMAC);
}

//region INET-STUFF

//gets ipv6
public String getLocalIpAddress()
{
    try
    {
        for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();)
        {
            NetworkInterface intf = en.nextElement();


            for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements();)
            {
                InetAddress inetAddress = enumIpAddr.nextElement();
                if (!inetAddress.isLoopbackAddress())
                {
                    return inetAddress.getHostAddress().toString();

                }
            }
        }
    }
    catch (SocketException ex)
    {
        Log.e("SRM", ex.toString());
    }
    return null;
}
//endregion
}

ToolsSelection 片段

public class ToolsSelectionFragment extends Fragment {

//region UI VARS
Button btnPing;
Button btnDns;
Button btnPortScan;
Button btnTraceRoute;
//endregion


private static final String ARG_SECTION_NUMBER = "section_number";
private OnFragmentInteractionListener mListener;

public ToolsSelectionFragment() {
    // Required empty public constructor
}

public static ToolsSelectionFragment newInstance(int sectionNumber) {
    ToolsSelectionFragment fragment = new ToolsSelectionFragment();
    Bundle args = new Bundle();
    args.putInt(ARG_SECTION_NUMBER, sectionNumber);
    fragment.setArguments(args);
    return fragment;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.fragment_tools_selection, container, false);
    initvar(v);
    registerButtonListeners();
    return v;
}


public void initvar(View view) {
    btnPing = (Button) view.findViewById(R.id.btnPing);
    btnDns = (Button) view.findViewById(R.id.btnDns);
    btnPortScan = (Button) view.findViewById(R.id.btnPortScan);
    btnTraceRoute = (Button) view.findViewById(R.id.btnTraceRoute);
}


public void registerButtonListeners() {
    btnPing.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(getActivity(), PingActivity.class);
            startActivity(intent);
        }
    });

    btnDns.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(getActivity(), DNSActivity.class);
            startActivity(intent);
        }
    });

    btnPortScan.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(getActivity(), PortscanActivity.class);
            startActivity(intent);
        }
    });

    btnTraceRoute.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(getActivity(), WhoisActivity.class);
            startActivity(intent);
        }
    });
}


// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
    if (mListener != null) {
        mListener.onFragmentInteraction(uri);
    }
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    if (context instanceof OnFragmentInteractionListener) {
        mListener = (OnFragmentInteractionListener) context;
    } else {
        throw new RuntimeException(context.toString()
                + " must implement OnFragmentInteractionListener");
    }
}

@Override
public void onDetach() {
    super.onDetach();
    mListener = null;
}

/**
 * This interface must be implemented by activities that contain this
 * fragment to allow an interaction in this fragment to be communicated
 * to the activity and potentially other fragments contained in that
 * activity.
 * <p>
 * See the Android Training lesson <a href=
 * "http://developer.android.com/training/basics/fragments/communicating.html"
 * >Communicating with Other Fragments</a> for more information.
 */
public interface OnFragmentInteractionListener {
    // TODO: Update argument type and name
    void onFragmentInteraction(Uri uri);
}
}

DevicesFragment：

public class devicesFragment extends Fragment implements myResultReceiver.Receiver {
public myResultReceiver mReceiver;
OnListFragmentInteractionListener mlistener;
Context context;
MydevicesRecyclerViewAdapter mydevAdapter;

private static ArrayList<Devices> devlist;
SharedPreferences netprefs;

// TODO: Customize parameter argument names
private static final String ARG_COLUMN_COUNT = "column-count";
private int mColumnCount = 1;
private OnListFragmentInteractionListener mListener;


public devicesFragment() {
}
// TODO: Customize parameter initialization
public static devicesFragment newInstance(int columnCount) {
    devicesFragment fragment = new devicesFragment();
    Bundle args = new Bundle();
    args.putInt(ARG_COLUMN_COUNT, columnCount);
    fragment.setArguments(args);
    return fragment;
}


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    if (getArguments() != null) {
        mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
    }
}


//TODO: populate devices list with a sharedPreferences list and double check there. also split up subnet into multiple threads to work faster.
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_devices_list, container, false);
    ((MainActivity) getActivity()).setActionBarTitle("Net Scan");


    devlist = new ArrayList<>();
    devlist.add(new Devices("TEST_DEVICE", true, "192.168.100.199", "00:00:00:00:00:00", true, "MOBILE", "meeseeks box"));
    devlist.add(new Devices("TEST_DEVICE2", true, "74.16.248.777", "11:11:11:11:11:11", true, "DESKTOP", "meeseeks box"));


    launchNetworkSniffer(0);
    // Set the adapter
    if (view instanceof RecyclerView) {
        Context context = view.getContext();


        RecyclerView recyclerView = (RecyclerView) view;
        if (mColumnCount <= 1) {
            recyclerView.setLayoutManager(new LinearLayoutManager(context));
        } else {
            recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
        }
        mydevAdapter = new MydevicesRecyclerViewAdapter(devlist, mListener);
        recyclerView.setAdapter(mydevAdapter);
    }
    return view;
}


//NetHelper intent service class startup
//discover network info, and get a list of devices
public void launchNetworkSniffer(int opr) {
    Intent serviceIntent = new Intent(getActivity(), NetHelper.class);

    //setup resultReceiver for service callbacks
    mReceiver = new myResultReceiver(new android.os.Handler());
    mReceiver.setReceiver(this);

    serviceIntent.putExtra(NetHelper.BUNDLE_RECEIVER, mReceiver);
    serviceIntent.putExtra("OPR", opr);
    getActivity().startService(serviceIntent);
}

@Override
public void onResume() {
    super.onResume();
    mReceiver.setReceiver(this);
}

//avoid leaks with result receiver

@Override
public void onPause() {
    super.onPause();
    mReceiver.setReceiver(null);
}


@Override
public void onAttach(Context context) {
    super.onAttach(context);

    // This makes sure that the container activity has implemented
    // the callback interface. If not, it throws an exception
    try {
        mlistener = (OnListFragmentInteractionListener) context;
    } catch (ClassCastException e) {
        throw new ClassCastException(context.toString()
                + " must implement listener");
    }
}

@Override
public void onDetach() {
    super.onDetach();
    mListener = null;
}



//receiver implemented methods
@Override
public void onReceiveResult(int resultCode, Bundle resultData) {
    Log.d("DATA_RECEIVED", "processing...");

    String newdevjson = resultData.getString("DATA_");
    Log.d("DATA_", newdevjson);

    Gson gson = new Gson();
    Devices newd = gson.fromJson(newdevjson, Devices.class);

    if (devlist != null) {
        for (Devices i : devlist) {
            if (i.getIp().equals(newd.getIp())) {
                return;
            }
        }
        Log.d("ADDING_FRAGDEVICE", newd.devName);
        devlist.add(newd);
        mydevAdapter.notifyItemInserted(devlist.size() -1);
        mydevAdapter.notifyDataSetChanged();
    }
}


public interface OnListFragmentInteractionListener {
    // TODO: Update argument type and name
    void onListFragmentInteraction(Devices device);
}
}

真的希望尽快解决这个问题。 感谢迄今为止尝试过的人。

Answer 1

使用 FragmentStatePagerAdapter 代替 FragmentPagerAdapter

 public  class MyAdapter extends FragmentStatePagerAdapter {
        public MyAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public int getCount() {
            return NUM_ITEMS;
        }

        @Override
        public Fragment getItem(int position) {
            return ArrayListFragment.newInstance(position);
        }
    }