我使用Navigation Drawer
在片段之间导航,它们都使用MainActivity工具栏,但每个片段都有自己的TabLayout
,其中有3个选项卡,在每个选项卡中,我使用RecyclerView
显示不同的文本和图像。
我上次用的是活动片而不是碎片,但现在用的是抽屉,用碎片更好。
我已经到了标签工作的地步,但是只要我把ViewPager
放进去,把适配器连接到标签上,我从抽屉里打开新的片段,我就会得到一个空指针,这里可能有什么问题?
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)
7条答案
按热度按时间ktca8awb1#
在查看您的代码后,我发现您忘记了在PagerAdapter的getItem方法中返回一个片段,该片段是您从FragmentStatePagerAdapter中覆盖的,并且在每种情况下都没有break语句,因此每次都返回一个空值。
要做到这一点,你需要为ViewPager中的每个页面创建另一个新片段,或者你可以创建一个新片段,可以在ViewPager的所有页面中使用。
您不能在父片段中定义的视图页的选项卡中使用相同的recyclerview。
activity_fragment_one.xml
我已经修复了你的片段,并创建了一个新的片段,你可以在ViewPager页面中使用。
查看分页器中每个页面的FragmentTab(或者您可以根据需要为每个页面创建不同的片段)。
fragment_tab.xml
7ajki6be2#
使用
getChildFragmentManager()
而不是getSupportFragmentManager()
nom7f22z3#
我建议在中使用
getChildFragmentManager
而不是getFragmentManager
viewPager.setAdapter(new PagerAdapter (getFragmentManager(), tabLayout.getTabCount()));
unftdfkk4#
如果没有错误日志,很难说出您在哪里以及为什么会得到
NullPointerException
。首先引起我注意的是,您没有链接
TabLayout
和ViewPager
。在为ViewPager
设置适配器后,使用以下代码:我不确定这是不是问题所在,但是给予吧:)
pzfprimi5#
嗯,不久前我实现了完全相同的应用程序设计。我有一个片段,它打算保存选项卡和ViewPager。这是一个棘手的任务,我记得我遇到了类似的问题,你没有。下面是我如何解决它:
布局顺序为:
Activity -> Fragment -> Tab Layout + ViewPager -> FragmentStatePagerAdapter -> Fragment -> RecyclerView
你的主要活动与你无关。所有的东西都是碎片。所以在你的
activity_main.xml
中去掉TabLayout。您必须行程页面巡览区中的巢状片段。所有页面内容都必须在那里,而且TabLayout必须与ViewPager位于相同的版面配置中。
我的项目有点老了,我使用了
android.support.v4.app.Fragment
,如果它有意义的话。我从你不需要的数据中剥离了源代码,所以你可能会看到引用了一些孤立的方法。该任务是显示价格列表与类别,并呈现每个类别的产品在自己的页面上,以便水平滑动将切换类别和垂直滑动-列表产品。
每个包含ViewPager和TabLayout的片段都具有以下
subfragment_price_list_pager.xml
布局:下面是
PriceListPagerFragment.class
:自定义
FragmentStatePagerAdapter
实施,PriceListCategoriesAdapter.class
:最后是
PriceListFragment
布局:PriceListFragment.class
本身没有什么特别的,只要用合适的数据示例化它的RecyclerView就可以了。sg24os4d6#
PagerAdapter
中getItem
方法错误,它返回Fragment
init您应该返回Fragment
而在片段中,您将setView
recyclerView
给它14ifxucb7#
**在容器内创建tabLayout和viewpager2可解决此问题
在导航抽屉中单击主页时:删除所有片段并显示tablayout和viewPager2,否则隐藏tablayout和viewPager2并加载片段**
XML文件
活动JAVA文件