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fragment 内的Android TabLayout

转载 作者:IT王子 更新时间:2023-10-28 23:36:17 26 4
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我正在使用 Navigation Drawer 在 fragment 之间导航,它们都使用 MainActivity 工具栏,但每个 fragment 都有自己的 TabLayout 和 3 个选项卡,并且在每个选项卡中我使用 RecyclerView 显示不同的文字和图片。

我上次使用的是 Activity 而不是 fragment ,但现在使用抽屉最好使用 fragment 。

我已经到了标签可以工作的地步,但是只要我将 ViewPager 放入并将适配器连接到标签,然后从抽屉中打开新 fragment ,我就会得到一个空指针这里可能是什么问题?

MainActivity.java

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);
}

@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) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
return id == R.id.action_settings || super.onOptionsItemSelected(item);

}

@Override
public boolean onNavigationItemSelected(MenuItem item) {
int id = item.getItemId();
Fragment fragment;

if (id == R.id.fragment_one) {
fragment = new NewFragment();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, fragment);
ft.commit();

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

fragment = new NewFragment();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, fragment);
ft.commit();

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

fragment = new NewFragment();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, fragment);
ft.commit();

}

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

activity_main.xml

<android.support.v4.widget.DrawerLayout 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/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">

<android.support.design.widget.CoordinatorLayout 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:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.xcandy.guideforfifa17.MainActivity">

<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>

<include layout="@layout/content_main" />

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

<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer" />

</android.support.v4.widget.DrawerLayout>

NewFragment.java

public class NewFragment extends Fragment {

private RecyclerView mRecyclerView;


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_fragment_one, container, false);

TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tabs);
tabLayout.addTab(tabLayout.newTab().setText("A"));
tabLayout.addTab(tabLayout.newTab().setText("B"));
tabLayout.addTab(tabLayout.newTab().setText("C"));

final ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewpager);

mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);

RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLayoutManager);


viewPager.setAdapter(new PagerAdapter
(getFragmentManager(), tabLayout.getTabCount()));
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.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) {

}
});

return view;
}

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:

RecyclerView.Adapter mAdapter = new AdapterOne();
mRecyclerView.setAdapter(mAdapter);

case 1:

mAdapter = new AdapterTwo();
mRecyclerView.setAdapter(mAdapter);

case 2:

mAdapter = new AdapterThree();
mRecyclerView.setAdapter(mAdapter);

default:
return null;
}
}

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

activity_fragment.xml

<android.support.design.widget.CoordinatorLayout 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:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context=".NewFragment">

<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">

<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:tabMode="fixed"
app:tabGravity="fill"/>

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

<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/white"/>

<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>

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

错误日志

                  --------- beginning of crash
06-23 11:19:56.985 2466-2466/com.candyx.sims E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.candyx.sims, PID: 2466
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.candyx.sims.BlankFragment.onCreateView(BlankFragment.java:38)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-23 11:23:14.912 5839-5873/com.candyx.sims D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true

[ 06-23 11:23:14.920 5839: 5839 D/ ]
HostConnection::get() New Host Connection established 0xb4125190, tid 5839
06-23 11:23:14.927 5839-5839/com.candyx.sims D/Atlas: Validating map...
06-23 11:23:15.011 5839-5873/com.candyx.sims I/OpenGLRenderer: Initialized EGL, version 1.4
06-23 11:23:15.027 5839-5873/com.candyx.sims D/OpenGLRenderer: Enabling debug mode 0
06-23 11:23:15.039 5839-5873/com.candyx.sims W/EGL_emulation: eglSurfaceAttrib not implemented
06-23 11:23:15.039 5839-5873/com.candyx.sims W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xae838600, error=EGL_SUCCESS
06-23 11:23:16.444 5839-5839/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:23:17.342 5839-5839/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:23:17.350 5839-5839/com.candyx.sims I/AppCompatViewInflater: app:theme is now deprecated. Please move to using android:theme instead.
06-23 11:23:17.369 5839-5839/com.candyx.sims D/AndroidRuntime: Shutting down VM
06-23 11:23:17.369 5839-5839/com.candyx.sims E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.candyx.sims, PID: 5839
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.candyx.sims.NewFragment.onCreateView(NewFragment.java:38)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-23 11:25:16.961 7518-7518/com.candyx.sims W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
06-23 11:25:17.078 7518-7548/com.candyx.sims D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true

[ 06-23 11:25:17.081 7518: 7518 D/ ]
HostConnection::get() New Host Connection established 0xb412a1f0, tid 7518
06-23 11:25:17.082 7518-7518/com.candyx.sims D/Atlas: Validating map...
06-23 11:25:17.109 7518-7548/com.candyx.sims I/OpenGLRenderer: Initialized EGL, version 1.4
06-23 11:25:17.126 7518-7548/com.candyx.sims D/OpenGLRenderer: Enabling debug mode 0
06-23 11:25:17.134 7518-7548/com.candyx.sims W/EGL_emulation: eglSurfaceAttrib not implemented
06-23 11:25:17.134 7518-7548/com.candyx.sims W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xb41234c0, error=EGL_SUCCESS
06-23 11:25:31.030 7518-7518/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:25:32.174 7518-7518/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:25:32.187 7518-7518/com.candyx.sims I/AppCompatViewInflater: app:theme is now deprecated. Please move to using android:theme instead.
06-23 11:25:32.207 7518-7518/com.candyx.sims D/AndroidRuntime: Shutting down VM
06-23 11:25:32.207 7518-7518/com.candyx.sims E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.candyx.sims, PID: 7518
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.candyx.sims.NewFragment.onCreateView(NewFragment.java:38)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

最佳答案

查看您的代码后,我发现您忘记在 PagerAdapter 的 getItem 方法中返回您从 FragmentStatePagerAdapter 覆盖的 fragment ,并且在每种情况下都没有 break 语句,因此每次返回了一个空值。

为此,您需要为 ViewPager 中的每个页面创建另一个新 fragment ,或者您可以创建一个可以在 ViewPager 的所有页面中使用的新 fragment 。

您不能在父 fragment 中定义的 View 寻呼机选项卡中使用相同的 recyclerview。

activity_fragment_one.xml

 <android.support.design.widget.CoordinatorLayout 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:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context=".NewFragment">

<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">

<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
app:tabTextAppearance="?android:attr/textAppearanceMedium"
app:tabTextColor="#ffffff"
android:layout_height="?android:actionBarSize"
app:tabMode="fixed"
app:tabGravity="fill"/>

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

<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:background="@android:color/white"/>
</android.support.design.widget.CoordinatorLayout>

我已经修复了您的 fragment 并创建了一个新的 fragment ,您可以在 ViewPager 页面中使用它。

public class NewFragment extends Fragment {

private RecyclerView mRecyclerView;


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_fragment_one, container, false);
TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tabs);
tabLayout.addTab(tabLayout.newTab().setText("A"));
tabLayout.addTab(tabLayout.newTab().setText("B"));
tabLayout.addTab(tabLayout.newTab().setText("C"));
final ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewpager);
// mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
LinearLayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
//mRecyclerView.setLayoutManager(mLayoutManager);
viewPager.setAdapter(new PagerAdapter(getFragmentManager(), tabLayout.getTabCount()));
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setupWithViewPager(viewPager);
tabLayout.setTabMode(TabLayout.MODE_SCROLLABLE);
tabLayout.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) {

}
});

return view;
}

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:
return new FragmentTab();
case 1:
return new FragmentTab();
case 2:
return new FragmentTab();

default:
return null;
}
}

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

View Pager 中每个页面的 FragmentTab(或者您可以根据需要为每个页面创建不同的 fragment )。

public class FragmentTab extends Fragment {
RecyclerView mRecyclerView;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_tab, container, false);

mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
LinearLayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
mRecyclerView.setLayoutManager(mLayoutManager);
RecyclerView.Adapter mAdapter = new AdapterOne();
mRecyclerView.setAdapter(mAdapter);
return view;
}
}

fragment_tab.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>


</LinearLayout>

关于 fragment 内的Android TabLayout,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/35058819/

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