android - java.lang.NullPointerException 尝试调用虚方法 ShimmerFrameLayout.startShimmer()

Question

我找不到任何可能的原因导致我面临空指针异常。当我尝试在中调用shimmerLayout.startShimmer();方法时，我正面临着它OnCreateView。我已经检查了几次 shimmerLayout 连接是否正常。但似乎我已经完美地将微光容器与 java 代码连接起来。我仍然面临空指针异常。我认为关于微光生命周期或其他任何事情，我不知道一些事情。我也调用了shimmerLayout.stopShimmer();ingetDataToArray()方法。

片段博客.xml

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".BlogFragment">


    <com.facebook.shimmer.ShimmerFrameLayout
        android:id="@+id/shimmerFrameLayout_blog"
        android:layout_width="match_parent"
        android:layout_height="match_parent">


        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

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

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

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

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

        </LinearLayout>
    </com.facebook.shimmer.ShimmerFrameLayout>


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView_blog"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/floatingActionButton_blog"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:layout_marginEnd="38dp"
        android:layout_marginBottom="68dp"
        android:clickable="true"
        android:src="@drawable/ic_add_black_24dp"
        app:backgroundTint="#0979D3"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.954"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.931" />
</RelativeLayout>

facebook_shimmer_item.xml

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

    <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


        <TextView
            android:id="@+id/textView12"
            android:layout_width="270dp"
            android:layout_height="wrap_content"
            android:layout_marginLeft="100dp"
            android:layout_marginTop="5dp"
            android:background="@color/content_text_color" />

        <TextView
            android:id="@+id/textView14"
            android:layout_width="94dp"
            android:layout_height="wrap_content"
            android:layout_marginLeft="100dp"
            android:layout_marginTop="40dp"
            android:background="@color/content_text_color" />

        <TextView
            android:id="@+id/textView13"
            android:layout_width="80dp"
            android:layout_height="77dp"
            android:layout_marginLeft="5dp"
            android:layout_marginTop="5dp"
            android:background="@color/content_text_color" />

    </androidx.cardview.widget.CardView>

    <TextView
        android:id="@+id/textView15"
        android:layout_width="380dp"
        android:layout_height="wrap_content"
        android:layout_marginLeft="5dp"
        android:layout_marginTop="10dp"
        android:background="@color/content_text_color" />

    <TextView
        android:id="@+id/textView16"
        android:layout_width="308dp"
        android:layout_height="wrap_content"
        android:layout_marginLeft="5dp"
        android:layout_marginTop="10dp"
        android:background="@color/content_text_color" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="220dp"
        android:orientation="horizontal">


        <ImageView
            android:id="@+id/imageView3"
            app:srcCompat="@drawable/ic_watchers"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="5dp" />

        <TextView
            android:id="@+id/textView_views"
            android:layout_width="20dp"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="0" />


        <ImageView
            android:id="@+id/imageView4"
            app:srcCompat="@drawable/ic_like"
            android:layout_width="18dp"
            android:layout_height="12dp"
            android:layout_marginTop="5dp" />

        <TextView
            android:id="@+id/textView_likes"
            android:layout_width="20dp"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="0" />


        <ImageView
            android:id="@+id/imageView2"
            app:srcCompat="@drawable/ic_comments"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="5dp" />

        <TextView
            android:id="@+id/textView_comments"
            android:layout_width="20dp"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="0" />


    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="34dp"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/textView18"
            android:layout_width="123dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="@color/content_text_color" />

        <TextView
            android:id="@+id/textView19"
            android:layout_width="128dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="@color/content_text_color" />
    </LinearLayout>

</LinearLayout>

博客片段.java

package com.example.farmersapp;

import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.example.farmersapp.adapter.ListBlogItem_Adapter;
import com.example.farmersapp.model.BlogItem;
import com.facebook.shimmer.ShimmerFrameLayout;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.DocumentReference;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.QueryDocumentSnapshot;
import com.google.firebase.firestore.QuerySnapshot;
import com.google.firebase.storage.StorageReference;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;


public class BlogFragment extends Fragment {

    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";
    private String mParam1;
    private String mParam2;

    public static final String TAG = "checked";

    //widgets
    private RecyclerView recyclerViewBlogItem;
    private FloatingActionButton floatingActionButton;
    private ShimmerFrameLayout shimmerFrameLayout;

    List<BlogItem> mBlogData;


  //Firebase
  private FirebaseAuth mAuth;
  private StorageReference storageReference;
  private CollectionReference collectionReferenceBlog,collectionReferenceBlogId,collectionReferenceusers;
  private FirebaseFirestore firebaseFirestore;
  private DocumentReference documentReferenceBlogId,documentReferenceBlog;


  //adapter
  ListBlogItem_Adapter adapter;



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


    public static BlogFragment newInstance(String param1, String param2) {
        BlogFragment fragment = new BlogFragment();
        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
        View contentView = inflater.inflate(R.layout.fragment_blog, container, false);

        floatingActionButton = contentView.findViewById(R.id.floatingActionButton_blog);
        recyclerViewBlogItem = contentView.findViewById(R.id.recyclerView_blog);
        shimmerFrameLayout = container.findViewById(R.id.shimmerFrameLayout_blog);
        mBlogData = new ArrayList<>();

        shimmerFrameLayout.startShimmer();

        mAuth = FirebaseAuth.getInstance();
        collectionReferenceBlog = FirebaseFirestore.getInstance().collection("Blog");

        floatingActionButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Fragment fragment = new AddNewBlogFragment();
                FragmentManager fragmentManager = requireActivity().getSupportFragmentManager();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

                fragmentTransaction.setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_right, R.anim.enter_from_right, R.anim.exit_to_right);
                fragmentTransaction.replace(R.id.container, fragment);
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
            }
        });

        setUpRecyclerViewManual();
        getDataToArray();



        return contentView;

    }


  private void getDataToArray() {



    collectionReferenceBlog.get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
      @Override
      public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
        if(queryDocumentSnapshots.isEmpty())
        {
          Log.d(TAG,"there is nothing in blog database");
        }
        else
        {
          List<BlogItem> data = queryDocumentSnapshots.toObjects(BlogItem.class);
          adapter = new ListBlogItem_Adapter(mBlogData, getContext());
          recyclerViewBlogItem.setAdapter(adapter);
          mBlogData.addAll(data);
          Log.d("checked success:", "ok " + mBlogData);
          shimmerFrameLayout.stopShimmer();
//            shimmerFrameLayout.setVisibility(View.GONE);
        }



      }
    }).addOnFailureListener(new OnFailureListener() {
      @Override
      public void onFailure(@NonNull Exception e) {
          Log.d(TAG, "blog data load failed");
      }
    });
  }

    private void setUpRecyclerViewManual() {
        recyclerViewBlogItem.setHasFixedSize(true);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this.getContext());
//    adapter = new AlternateListAdapter_Market(mData,this.getContext());
//    marketRecyleView.setAdapter(adapter);
        Log.d("checked", "adapter called");
        recyclerViewBlogItem.setLayoutManager(layoutManager);
    }

}

例外

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.farmersapp, PID: 27402
    java.lang.NullPointerException: Attempt to invoke virtual method 'void com.facebook.shimmer.ShimmerFrameLayout.startShimmer()' on a null object reference
        at com.example.farmersapp.BlogFragment.onCreateView(BlogFragment.java:106)
        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.execPendingActions(FragmentManager.java:1849)
        at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)