ViewPager没有显示片段

Question

我无法让它发挥作用。基本应用程序的功能应该如此，但其中一个布局文件上的ViewPager根本不显示任何片段。我多次检查代码，但我找不到错误。当我尝试调试它时，我注意到它甚至没有初始化它在选择选项卡时应该使用的片段类。 我的主要活动：

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    new GetData(this).execute();

    TabLayout tab_layout = (TabLayout) findViewById(R.id.tab_layout);
    tab_layout.addTab(tab_layout.newTab().setText("CASUAL"));
    tab_layout.addTab(tab_layout.newTab().setText("RANKED"));
    tab_layout.setTabGravity(TabLayout.GRAVITY_FILL);

    final ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
    PagerAdapter adapter = new PagerAdapter(getSupportFragmentManager(), tab_layout.getTabCount());
    viewPager.setAdapter(adapter);
    tab_layout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {

        }
    });

}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.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();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.nav_stats) {
        // Handle the camera action
    } else if (id == R.id.nav_about) {

    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}
}

我的PagerAdapter：

public class PagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;

public PagerAdapter(FragmentManager fm, int NumOfTabs) {
    super(fm);
    this.mNumOfTabs = NumOfTabs;
    }

@Override
public Fragment getItem(int position) {

    switch (position) {
        case 0:
            CasualStats tab1 = new CasualStats();
            return tab1;
        case 1:
            RankedStats tab2 = new RankedStats();
            return tab2;
        default:
            return null;
        }
     }

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

使用ViewPager进行布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"><![CDATA[

        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:layout_below="@id/tab_layout"/>
]]>

<android.support.design.widget.TabLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true"
    android:id="@+id/tab_layout">

</android.support.design.widget.TabLayout>

<view
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    class="android.support.v4.view.ViewPager"
    android:layout_alignParentStart="true"
    android:id="@+id/view_pager"
    android:layout_below="@+id/tab_layout" />

</RelativeLayout>

应该在ViewPager中显示的选项卡片段的类只是普通的自动生成的Android Studio片段类。

其中一个片段：

public class CasualStats extends Fragment{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";

// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;

private OnFragmentInteractionListener mListener;

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

/**
 * Use this factory method to create a new instance of
 * this fragment using the provided parameters.
 *
 * @param param1 Parameter 1.
 * @param param2 Parameter 2.
 * @return A new instance of fragment CasualStats.
 */
// TODO: Rename and change types and number of parameters
public static CasualStats newInstance(String param1, String param2) {
    CasualStats fragment = new CasualStats();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

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

// 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 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);
}
}

xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.app.anzel.r6s.CasualStats">

<!-- TODO: Update blank fragment layout -->

<TextView
    android:text="1st fragment"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true"
    android:layout_marginStart="28dp"
    android:layout_marginTop="22dp"
    android:id="@+id/textView"
    android:visibility="visible" />
</RelativeLayout>

Answer 1

问题是您有嵌套的片段并使用getFragmentManager（）;您应该改用getChildFragmentManager（）。

java：

viewPagerAdapter = new PagerAdapter(getChildFragmentManager())

kotlin：

viewPagerAdapter = PagerAdapter(childFragmentManager)

Answer 2

我觉得有点愚蠢。问题出在我怀疑的ViewPager上。经过3小时的代码调试后，我只是将ViewPager从带有选项卡的布局移动到另一个布局，该布局基本上连接了所有布局。

Answer 3

您遗失.id，而且您不需要setupWithViewPager：

setOnTabSelectedListener

让我们看看这里： http://www.androidhive.info/2015/09/android-material-design-working-with-tabs/

你必须在适配器中覆盖tab_layout.setupWithViewPager(viewPager) 并返回标签标题。

最后，不要在xml中使用getPageTitle，创建正常的xml视图：

<view ..class>

Answer 4

试试这个：

布局中的

：

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<android.support.design.widget.TabLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true"
    android:id="@+id/tab_layout">

</android.support.design.widget.TabLayout>

<android.support.v4.view.ViewPager
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_alignParentStart="true"
    android:id="@+id/view_pager"
    android:layout_below="@+id/tab_layout" />

</RelativeLayout>

活动：

 TabLayout tab_layout = (TabLayout) findViewById(R.id.tab_layout);
    tab_layout.addTab(tab_layout.newTab().setText("CASUAL"));
    tab_layout.addTab(tab_layout.newTab().setText("RANKED"));
    tab_layout.setTabGravity(TabLayout.GRAVITY_FILL);

    final ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
    PagerAdapter adapter = new PagerAdapter(getSupportFragmentManager(), tab_layout.getTabCount());
    viewPager.setAdapter(adapter);
    viewPager.setOffscreenPageLimit(2);
    tab_layout.post(new Runnable() {
    @Override
    public void run() {
        tab_layout.setupWithViewPager(viewPager);
      }
   });
    tab_layout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {

        }
    });

PagerAdapter：

    public class PagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;

// an array of tab titles
    private String tabTitles[] = new String[]{"CASUAL", "RANKED"};

public PagerAdapter(FragmentManager fm, int NumOfTabs) {
    super(fm);
    this.mNumOfTabs = NumOfTabs;
    }

@Override
public Fragment getItem(int position) {

    switch (position) {
        case 0:
            CasualStats tab1 = new CasualStats();
            return tab1;
        case 1:
            RankedStats tab2 = new RankedStats();
            return tab2;
        default:
            return null;
        }
     }

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

     @Override
    public CharSequence getPageTitle(int position) {
        return tabTitles[position];
    }
}

Answer 5

下面的示例代码可以正常使用viewpager和tabs。尝试一下。

1. 主要活动布局

   <android.support.design.widget.AppBarLayout
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:theme="@style/AppTheme.AppBarOverlay">
   
       <android.support.v7.widget.Toolbar
           android:id="@+id/toolbar"
           android:layout_width="match_parent"
           android:layout_height="?attr/actionBarSize"
           android:background="?attr/colorPrimary"
           app:popupTheme="@style/AppTheme.PopupOverlay" />
   
   </android.support.design.widget.AppBarLayout>
   
   <android.support.design.widget.TabLayout
       android:id="@+id/tab_container"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:layout_marginTop="?attr/actionBarSize" />
   
   <include layout="@layout/content_main" />
   
   <android.support.design.widget.FloatingActionButton
       android:id="@+id/fab"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_gravity="bottom|end"
       android:layout_margin="@dimen/fab_margin"
       app:srcCompat="@android:drawable/ic_dialog_email" />
   

然后是viewpager容器布局

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/content_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginTop="?attr/actionBarSize"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.test.myapplication.MainActivity"
    tools:showIn="@layout/app_bar_main">

    <android.support.v4.view.ViewPager
        android:id="@+id/page_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#FF0000" />
</RelativeLayout>

以下是主要活动部分：

package com.test.myapplication;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TabLayout;
import android.support.v4.app.*;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        ViewPager pager = (ViewPager)findViewById(R.id.page_container);
        pager.setAdapter(new Adapter(getSupportFragmentManager()));
        TabLayout tabs = (TabLayout)findViewById(R.id.tab_container);
        tabs.setupWithViewPager(pager, true);
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camera) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }


    public static class Adapter extends FragmentStatePagerAdapter {
        private String[] titles = new String[] {"ONE", "TWO"};

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

        @Override
        public Fragment getItem(int position) {
            switch (position){
                case 0:
                    return new com.test.myapplication.Fragment();
                case 1:
                    return new Fragment1();
            }
            return null;
        }

        @Override
        public int getCount() {
            return 2;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return titles[position];
        }
    }
}

Answer 6

如果您在 NestedScrollView 中使用带有 viewpager 的任何 tablayout，请确保将 --stacktrace --info --scan Reference 在嵌套滚动视图中。请注意，如果您使用导航抽屉，您的片段可能没有嵌套滚动视图，但您的活动片段容器可能位于嵌套滚动视图内。因为即使是带有背景颜色的空布局（用于调试问题）也不会显示，所以在我的情况下，这不是视图分页器的问题，而是嵌套滚动视图的问题。

<块引用>

调试提示：代替viewpager，放置一些布局并设置一个 背景颜色以查看布局是否可见。如果布局本身 不可见，那么您的父布局有问题，大多数 可能是 NestedScrollView。