java - RecyclerView onClickListener 显示错误

Question

我正在使用 Java 和 Firebase 开发一个 Android 应用。我想将一个 onClickListener 添加到我的 recyclerView 中，将其定向到显示内容的其他 Activity 。我的问题是，当我向适配器添加 onClickListener 时，应用程序将崩溃。 Logcat 显示了这些错误。

2020-04-12 12:46:06.382 14440-14440/com.eNotification.getnotify E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.eNotification.getnotify, PID: 14440
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RelativeLayout.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.eNotification.getnotify.ImageAdapter.onBindViewHolder(ImageAdapter.java:50)
        at com.eNotification.getnotify.ImageAdapter.onBindViewHolder(ImageAdapter.java:20)
        at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7065)
        at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7107)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2303)
        at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1627)
        at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
        at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at androidx.swiperefreshlayout.widget.SwipeRefreshLayout.onLayout(SwipeRefreshLayout.java:625)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1083)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:446)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1791)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1635)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1544)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:764)
        at android.view.View.layout(View.java:19693)
        at android.view.ViewGroup.layout(ViewGroup.java:6079)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2541)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2257)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1437)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6886)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1029)
        at android.view.Choreographer.doCallbacks(Choreographer.java:841)
        at android.view.Choreographer.doFrame(Choreographer.java:772)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1015)
2020-04-12 12:46:06.383 14440-14440/com.eNotification.getnotify E/AndroidRuntime:     at android.os.Handler.handleCallback(Handler.java:794)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:176)
        at android.app.ActivityThread.main(ActivityThread.java:6651)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824) 

这是我的代码。

主要 Activity

package com.eNotification.getnotify;

import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.Query;
import com.google.firebase.database.ValueEventListener;

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


public class MainActivityHomePage extends AppCompatActivity {
    private RecyclerView mRecyclerView;
    private ImageAdapter mAdapter;

    private ProgressBar mProgressCircle;

    private DatabaseReference mDatabaseRef;
    private List<Upload> mUploads;

    private SwipeRefreshLayout swipeRefreshLayout;

    private FirebaseAuth mAuth;


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

        mRecyclerView = findViewById(R.id.recyclerView);
        mRecyclerView.setHasFixedSize(true);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mProgressCircle = findViewById(R.id.progressCircle);
        mUploads = new ArrayList<>();

        mAuth = FirebaseAuth.getInstance();
        mDatabaseRef = FirebaseDatabase.getInstance().getReference("Messages");
        read();

    }

        private void read(){
        mDatabaseRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot postSnapshot : dataSnapshot.getChildren()){
                    Upload upload = postSnapshot.getValue(Upload.class);
                    mUploads.add(upload);
                }
                LinearLayoutManager linearLayoutManager = new LinearLayoutManager(MainActivityHomePage.this);
                linearLayoutManager.setReverseLayout(true);
                linearLayoutManager.setStackFromEnd(true);
                mRecyclerView.setLayoutManager(linearLayoutManager);
                mAdapter = new ImageAdapter(MainActivityHomePage.this,mUploads);
                mRecyclerView.setAdapter(mAdapter);
                mProgressCircle.setVisibility(View.INVISIBLE);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(MainActivityHomePage.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
                mProgressCircle.setVisibility(View.INVISIBLE);
            }
        });

        swipeRefreshLayout = findViewById(R.id.swipeRefreshLoyout);
        swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                swipeRefreshLayout.setRefreshing(false);
            }
        });
    }

    /*@Override
    protected void onStart() {
        super.onStart();

        FirebaseUser currentUser = FirebaseAuth.getInstance().getCurrentUser();
        if (currentUser == null){
            backToLogin();
            }
    }*/

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.slide_button,menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()){
            case R.id.other:
            case R.id.logout:
                logout();

        }
        return super.onOptionsItemSelected(item);
    }

    private void logout(){
        mAuth.signOut();
        backToLogin();
        Toast.makeText(this, "Logout successful", Toast.LENGTH_SHORT).show();
    }

    private void backToLogin() {
        Intent intent = new Intent(MainActivityHomePage.this,MainActivityLogIn.class);
        startActivity(intent);
        finish();
    }
}

适配器类

package com.eNotification.getnotify;

import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.squareup.picasso.Picasso;

import java.util.List;

public class ImageAdapter extends RecyclerView.Adapter<ImageAdapter.ImageViewHolder> {

    private Context mContext;
    private List<Upload> mUploads;

    public ImageAdapter(Context context,List<Upload> uploads){
        mContext = context;
        mUploads = uploads;
    }

    @NonNull
    @Override
    public ImageViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(mContext).inflate(R.layout.activity_card_view,parent,false);
        return new ImageViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull ImageViewHolder holder, int position) {
        final Upload uploadCurrent = mUploads.get(position);
        holder.hTitle.setText(uploadCurrent.getTitle());
        holder.hDesc.setText(uploadCurrent.getDescription());
        holder.hDate.setText(uploadCurrent.getDate());
        holder.hTime.setText(uploadCurrent.getTime());
        Picasso.get()
                .load(uploadCurrent.getImage())
                .fit()
                .centerInside()
                .into(holder.hImage);

        holder.parentLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(mContext,MainActivityEventView.class);
                intent.putExtra("mTitle",uploadCurrent.getTitle());
                intent.putExtra("mDescription",uploadCurrent.getDescription());
                intent.putExtra("mDate",uploadCurrent.getDate());
                intent.putExtra("mTime",uploadCurrent.getTime());
                intent.putExtra("imageUrl",uploadCurrent.getImage());
                intent.putExtra("sentDate",uploadCurrent.getSentDate());

                mContext.startActivity(intent);
            }
        });
    }
    @Override
    public int getItemCount() {
        return mUploads.size();
    }

    public class ImageViewHolder extends RecyclerView.ViewHolder{
            public TextView hTitle,hDesc,hDate,hTime;
            public ImageView hImage;
            public RelativeLayout parentLayout;

            public ImageViewHolder(View itemView){
                super(itemView);

                hTitle = itemView.findViewById(R.id.hTitle);
                hDesc = itemView.findViewById(R.id.hDescription);
                hDate = itemView.findViewById(R.id.hDate);
                hTime = itemView.findViewById(R.id.hTime);
                hImage = itemView.findViewById(R.id.hImage);
                parentLayout = itemView.findViewById(R.id.parentLayout);
            }
        }
}

模型类

package com.eNotification.getnotify;

public class Upload {
    private String mTitle;
    private String mDescription;
    private String mDate;
    private String mTime;
    private String imageUrl;
    private String sentDate;
    private String msgKey;

    public Upload() {

    }


    public Upload(String title,String desc,String date,String time,String image, String sDate,String mKey){
        /*if (title.trim().equals("") && desc.trim().equals("") && date.trim().equals("") && time.trim().equals("") && image.trim().equals("")){
            title = "No Value";
            desc = "No Value";
            date = "No Value";
            time = "No Value";
        }*/
        mTitle = title;
        mDescription = desc;
        mDate = date;
        mTime = time;
        imageUrl = image;
        sentDate = sDate;
        msgKey = mKey;
    }

    public String getTitle(){
        return mTitle;
    }

    public void setTitle(String title){
        mTitle = title;
    }

    public String getDescription(){
        return mDescription;
    }

    public void setDescription(String desc){
        mDescription = desc;
    }

    public String getDate(){
        return mDate;
    }

    public void setDate(String date){
        mDate = date;
    }

    public String getTime(){
        return mTime;
    }

    public void setTime(String time){
        mTime = time;
    }

    public String getImage(){
        return imageUrl;
    }

    public void setImage(String image){
        imageUrl = image;
    }

    public String getSentDate() {
        return sentDate;
    }

    public void setSentDate(String sDate) {
        this.sentDate = sDate;
    }

    public String getMsgKey() {
        return msgKey;
    }

    public void setMsgKey(String msgKey) {
        this.msgKey = msgKey;
    }
}

此类在点击时显示recyclerview的内容。

package com.eNotification.getnotify;

import android.os.Bundle;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

import com.squareup.picasso.Picasso;

public class MainActivityEventView extends AppCompatActivity {
    private static final String TAG = "GalleryActivity";

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


    private void getIncomingIntent(){
        if (getIntent().hasExtra("mTitle") && getIntent().hasExtra("mDescription")
                && getIntent().hasExtra("mDate") && getIntent().hasExtra("mTime")
                && getIntent().hasExtra("imageUrl") && getIntent().hasExtra("sentDate")){

            String mTitle = getIntent().getStringExtra("mTitle");
            String mDescription = getIntent().getStringExtra("mDescription");
            String mDate = getIntent().getStringExtra("mDate");
            String mTime = getIntent().getStringExtra("mTime");
            String imageUrl = getIntent().getStringExtra("imageUrl");
            String sentDate = getIntent().getStringExtra("sentDate");
            setImage(mTitle,mDescription,mDate,mTime,imageUrl,sentDate);
        }
    }

    private void setImage(String mTitle, String mDescription, String mDate,String mTime, String imageUrl, String sentDate){

        TextView title = findViewById(R.id.eventTitle);
        title.setText(mTitle);
        TextView description = findViewById(R.id.eventDescription);
        description.setText(mDescription);
        TextView date = findViewById(R.id.eventDate);
        date.setText(mDate);
        TextView time = findViewById(R.id.eventTime);
        time.setText(mTime);
        TextView sentDay = findViewById(R.id.eventSentDate);
        sentDay.setText(sentDate);

        ImageView image = findViewById(R.id.eventImage);
        Picasso.get().load(imageUrl).into(image);

    }

}

单击时用于显示 RecyclerView 内容的 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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp"
    tools:context=".MainActivityEventView">

    <ImageView
        android:id="@+id/eventImage"
        android:layout_width="match_parent"
        android:layout_height="300dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_image_black_24dp" />

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="370dp"
        android:padding="10dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent">

        <TextView
            android:id="@+id/eventDate"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="TextView"
            android:textSize="15sp"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/eventTime"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="10dp"
            android:textSize="15sp"
            android:text="TextView"
            app:layout_constraintStart_toEndOf="@+id/eventDate"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/eventTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="10dp"
            android:textSize="20sp"
            android:textStyle="bold"
            android:lines="2"
            android:text="TextView"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/eventDate" />

        <TextView
            android:id="@+id/eventDescription"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="10dp"
            android:textSize="18sp"
            android:text="TextView"
            android:lines="40"
            android:minLines="10"
            android:gravity="top|start"
            android:scrollbars="vertical"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/eventTitle" />

        <TextView
            android:id="@+id/eventSentDate"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="TextView"
            android:textSize="12sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/eventDescription" />

    </androidx.constraintlayout.widget.ConstraintLayout>


</androidx.constraintlayout.widget.ConstraintLayout>

activity_card_view

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView 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="200dp"
    app:cardBackgroundColor="@android:color/white"
    android:layout_marginTop="10dp"
    app:cardCornerRadius="8dp"
    app:cardElevation="2dp"
    app:cardPreventCornerOverlap="true">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/silver"
        android:padding="5dp">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:padding="5dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">

            <ImageView
                android:id="@+id/hImage"
                android:layout_width="250dp"
                android:layout_height="match_parent"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent" />
        </androidx.constraintlayout.widget.ConstraintLayout>

        <TextView
            android:id="@+id/hTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Title"
            android:maxLines="1"
            android:paddingStart="10dp"
            android:textColor="@color/black"
            android:textSize="20sp"
            android:textStyle="bold"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/hTime" />

        <TextView
            android:id="@+id/hDescription"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Description"
            android:maxLines="2"
            android:paddingStart="10dp"
            android:textColor="@color/black"
            android:textSize="16sp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/hTitle" />

        <TextView
            android:id="@+id/hDate"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:hint="Date"
            android:paddingStart="10dp"
            android:paddingEnd="10dp"
            android:textColor="@color/black"
            android:textSize="16sp"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/hTime"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="10dp"
            android:paddingStart="10dp"
            android:paddingEnd="10dp"
            android:textColor="@color/black"
            android:textSize="16sp"
            app:layout_constraintStart_toEndOf="@+id/hDate"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</androidx.cardview.widget.CardView>

activity_home_page 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"
    android:id="@+id/parentLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="8dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <ProgressBar
        android:id="@+id/progressCircle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true" />

    <androidx.swiperefreshlayout.widget.SwipeRefreshLayout
        android:id="@+id/swipeRefreshLoyout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:reverseLayout="true"/>

    </androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

</RelativeLayout>

我是初学者，不知道如何解决这个问题。任何帮助都会很棒。

Answer 1

试试这个，也许这会有所帮助 不要在 ImageViewHolder 中声明变量 RelativeLayout ParentLayout，而是在 ImageViewHolder 构造函数中存储 mView = itemView 后声明 View mView 然后在onBindViewHolder方法中holder.mView.setOnClickListener