问题描述
限时送ChatGPT账号..我在我的应用程序中添加了 tabLayout
并且 tabLayout
有 3 个表来显示三个不同的页面,现在我尝试将一个表设为 INVISIBLE 但我做不到.
我试着这样做
tabCalls.setVisibility(View.INVISIBLE);
但那行不通
Logcat 错误..
ava.lang.NullPointerException:尝试在空对象引用上调用虚拟方法void android.view.View.setVisibility(int)"在 com.example.myapplication.Fragmantmarket.MainActivityFargmain.TableInVisable(MainActivityFargmain.java:137)在 com.example.myapplication.Fragmantmarket.AboutUser.onCreateView(AboutUser.java:69)在 androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)在 androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320)在 androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187)在 androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1356)在 androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1434)在 androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1497)在 androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)在 androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2169)在 androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1992)在 androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1947)在 androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1818)在 androidx.fragment.app.BackStackRecordmitNowAllowingStateLoss(BackStackRecord.java:303)在 androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:246)在 androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)在 androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)在 androidx.viewpager.widget.ViewPager$3.run(ViewPager.java:273)在 android.view.Choreographer$CallbackRecord.run(Choreographer.java:927)在 android.view.Choreographer.doCallbacks(Choreographer.java:702)在 android.view.Choreographer.doFrame(Choreographer.java:635)在 android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:913)在 android.os.Handler.handleCallback(Handler.java:751)在 android.os.Handler.dispatchMessage(Handler.java:95)在 android.os.Looper.loop(Looper.java:154)在 android.app.ActivityThread.main(ActivityThread.java:6682)在 java.lang.reflect.Method.invoke(Native Method)在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
完整代码
<预><代码>公共类 MainActivityFargmain 扩展 AppCompatActivity {工具栏工具栏;TabLayout tabLayout;ViewPager viewPager;AdapterTableViewOrder 适配器TableViewOrder;TabItem tabChats;TabItem tabStatus;TabItem tabCalls;@覆盖protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.m_fragmant_view);工具栏 = findViewById(R.id.toolbar);工具栏.setTitle(getResources().getString(R.string.app_name));setSupportActionBar(工具栏);getSupportActionBar().setDisplayHomeAsUpEnabled(true);getSupportActionBar().setHomeButtonEnabled(true);tabLayout = findViewById(R.id.tablayout);tabChats = findViewById(R.id.tabChats);tabStatus = findViewById(R.id.tabStatus);tabCalls = findViewById(R.id.tabCalls);//我想要 INVISIBLEviewPager = findViewById(R.id.viewPager);tabCalls.setVisibility(View.INVISIBLE);//就像我尝试做的那样adapterTableViewOrder = new AdapterTableViewOrder(getSupportFragmentManager(), tabLayout.getTabCount());viewPager.setAdapter(adapterTableViewOrder);tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {@覆盖public void onTabSelected(TabLayout.Tab tab) {viewPager.setCurrentItem(tab.getPosition());}@覆盖public void onTabUnselected(TabLayout.Tab tab) {}@覆盖public void onTabReselected(TabLayout.Tab tab) {}});viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));}}xml 代码
<预><代码><com.google.android.material.tabs.TabItemandroid:id="@+id/tabChats"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Table1"/><com.google.android.material.tabs.TabItemandroid:id="@+id/tabStatus"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Table2"/><com.google.android.material.tabs.TabItemandroid:id="@+id/tabCalls"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Table3"/></com.google.android.material.tabs.TabLayout><androidx.viewpager.widget.ViewPagerandroid:id="@+id/viewPager"android:layout_width="match_parent"android:layout_height="wrap_content"/></LinearLayout>如果有人知道什么是错误,请告诉我.
解决方案你得到 NullPointerException
的问题,因为 TabItem
是一个特殊的小部件,不能膨胀使用 findViewById()
.
相反,要在您的活动/片段中增加 TabItem
:
TabLayout tabLayout = findViewById(R.id.tablayout);//第一个标签项查看 item0 = ((ViewGroup) tabLayout.getChildAt(0)).getChildAt(0);//第二个标签项查看 item0 = ((ViewGroup) tabLayout.getChildAt(0)).getChildAt(1);
注意它从索引 0 开始.所以第一个标签索引是 0.
要在您的代码中解决此问题:
删除这些行
TabItem tabCalls;...tabCalls = findViewById(R.id.tabCalls);//我想要 INVISIBLE
并添加
查看tabCalls;...//tabCalls 是第三项,所以我们使用索引为 2tabCalls == ((ViewGroup) tabLayout.getChildAt(0)).getChildAt(2);
然后就可以正常设置可见性了
tabCalls.setVisibility(View.INVISIBLE);
I add tabLayout
in my app and that tabLayout
have 3 table to display three different pages now I try to make one table as INVISIBLE but I can't do it.
I try to do it like that
tabCalls.setVisibility(View.INVISIBLE);
but that not work
Logcat error ..
ava.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
at com.example.myapplication.Fragmantmarket.MainActivityFargmain.TableInVisable(MainActivityFargmain.java:137)
at com.example.myapplication.Fragmantmarket.AboutUser.onCreateView(AboutUser.java:69)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1356)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1434)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1497)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)
at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2169)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1992)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1947)
at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1818)
at androidx.fragment.app.BackStackRecordmitNowAllowingStateLoss(BackStackRecord.java:303)
at androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:246)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)
at androidx.viewpager.widget.ViewPager$3.run(ViewPager.java:273)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:927)
at android.view.Choreographer.doCallbacks(Choreographer.java:702)
at android.view.Choreographer.doFrame(Choreographer.java:635)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:913)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
full code
public class MainActivityFargmain extends AppCompatActivity {
Toolbar toolbar;
TabLayout tabLayout;
ViewPager viewPager;
AdapterTableViewOrder adapterTableViewOrder;
TabItem tabChats;
TabItem tabStatus;
TabItem tabCalls;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.m_fragmant_view);
toolbar = findViewById(R.id.toolbar);
toolbar.setTitle(getResources().getString(R.string.app_name));
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
tabLayout = findViewById(R.id.tablayout);
tabChats = findViewById(R.id.tabChats);
tabStatus = findViewById(R.id.tabStatus);
tabCalls = findViewById(R.id.tabCalls);// That I want INVISIBLE
viewPager = findViewById(R.id.viewPager);
tabCalls.setVisibility(View.INVISIBLE);// like that I try to do
adapterTableViewOrder = new AdapterTableViewOrder(getSupportFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(adapterTableViewOrder);
tabLayout.addOnTabSelectedListener(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) {
}
});
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
}
}
xml code
<com.google.android.material.tabs.TabItem
android:id="@+id/tabChats"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Table1" />
<com.google.android.material.tabs.TabItem
android:id="@+id/tabStatus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Table2" />
<com.google.android.material.tabs.TabItem
android:id="@+id/tabCalls"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Table3" />
</com.google.android.material.tabs.TabLayout>
<androidx.viewpager.widget.ViewPager
android:id="@+id/viewPager"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
If anyone know what is error tell me.
解决方案The problem that you got NullPointerException
because the TabItem
is a special widget that can't be inflated using findViewById()
.
Instead, to inflate a TabItem
in your activity/fragment:
TabLayout tabLayout = findViewById(R.id.tablayout);
// First TabItem
View item0 = ((ViewGroup) tabLayout.getChildAt(0)).getChildAt(0);
// Second TabItem
View item0 = ((ViewGroup) tabLayout.getChildAt(0)).getChildAt(1);
Notice it starts with index 0. So the first tab index is 0.
To fix that in your code:
Remove these lines
TabItem tabCalls;
...
tabCalls = findViewById(R.id.tabCalls);// That I want INVISIBLE
And add
View tabCalls;
...
// tabCalls is the third item, so we used index of 2
tabCalls = = ((ViewGroup) tabLayout.getChildAt(0)).getChildAt(2);
Then you can set the visibility normally
tabCalls.setVisibility(View.INVISIBLE);
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