更改组件可见性时，Android Studio空对象引用错误

如何解决更改组件可见性时，Android Studio空对象引用错误

我正在制作一个为不同用户显示相同菜单的应用程序，每个菜单都是一个片段，但是根据用户的不同，某些内容是可见的，而其他内容则不是。

但是，当我尝试将组件的可见性设置为GONE时，出现空指针异常错误，我仍在测试，因此我仅在片段xml上使用textView。

我已经尝试在TextView方法之前的if子句中初始化FragmentMenuEncomenda和onCreate()这两个我正在使用的片段类对象。在setContentView()之后，例如tabLayout和viewPager。

if子句仅用于确保用户类型正确，并且所涉及的代码如下：

public class PaginaInicialCliente extends AppCompatActivity {

    private SharedPreferences sharedpreferences;

    private TabLayout tabLayout;
    private ViewPager viewPager;

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

        tabLayout = findViewById(R.id.tabLayoutCliente);
        viewPager = findViewById(R.id.viewPagerCliente);
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());

        //fragments a adicionar
        adapter.addFragment(new FragmentMenuEncomendas(),"Encomendas");
        adapter.addFragment(new FragmentMenuOpcoes(),"Opções");

        //inicializar o tab layout
        viewPager.setAdapter(adapter);
        tabLayout.setupWithViewPager(viewPager);

        sharedpreferences = getSharedPreferences("user",Context.MODE_PRIVATE);

        if (sharedpreferences.getInt("tipo",0)==3) {
            Log.d("USER_DEBUG","Cliente");
            FragmentMenuEncomendas fragmentMenuEncomendas = new FragmentMenuEncomendas();
            
            //THE ERROR IS HERE
            fragmentMenuEncomendas.getActivity().findViewById(R.id.textViewEncomendas).setVisibility(View.GONE);
        }

    }
}

FragmentMenuEncomenda类：

public class FragmentMenuEncomendas extends Fragment {

    View v;

    public FragmentMenuEncomendas(){
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
        v = inflater.inflate(R.layout.encomendas_fragment,container,false);
        return v;
    }
}

xml文件：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/textViewEncomendas"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_name"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

我搜索的所有答案均不起作用，我不知道是否是因为我正在尝试更改on create方法中的可见性。

解决方法

因为调用该函数时未创建视图。

public class FragmentMenuEmpresas extends Fragment {

    View v;
    View textView;
    boolean isTextViewShow = false;
    boolean isViewCreated = false;

    public FragmentMenuEmpresas() {
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
        v = inflater.inflate(R.layout.empresas_fragment,container,false);
        textView = v.findViewById(R.id.textViewEncomendas);
        return v;
    }

    @Override
    public void onViewCreated(@NonNull View view,@Nullable Bundle savedInstanceState) {
        super.onViewCreated(view,savedInstanceState);

        if (isTextViewShow) {

            textView.setVisibility(View.VISIBLE);
        } else {

            textView.setVisibility(View.GONE);
        }

        isViewCreated = true;
    }

    void setIsTextViewShow() {

        if (isViewCreated) {

            textView.setVisibility(View.VISIBLE);
        } else {

            isTextViewShow = true;
        }
    }

    void setIsTextViewGone() {
        
        if (isViewCreated) {

            textView.setVisibility(View.GONE);
        } else {

            isTextViewShow = false;
        }
    }
}

然后您可以随时拨打setIsTextViewShow 或setIsTextViewGone

 FragmentMenuEncomendas fragmentMenuEncomendas = new FragmentMenuEncomendas();
                       
 fragmentMenuEncomendas.setIsTextViewShow();//show
 fragmentMenuEncomendas.setIsTextViewGone();//gone