我尝试运行我的程序，但我得到这个错误。我已经尝试了一切，但我仍然得到这个错误。我不知道为什么会发生这种情况，因为我检查了HomeActivity.java，如果帖子被喜欢或不避免NullPointerException
错误:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageButton.setImageResource(int)' on a null object reference
at com.sm.socialmeme.HomeActivity$1.onDataChange(HomeActivity.java:94)
at com.google.firebase.database.Query$1.onDataChange(Query.java:189)
at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7562)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
我的firebase实时数据库
HomeActivity.java:
package com.sm.socialmeme;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.content.ContentResolver;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.webkit.MimeTypeMap;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import android.widget.Toast;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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 com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;
import com.google.firebase.storage.UploadTask;
import org.jetbrains.annotations.NotNull;
import java.util.ArrayList;
import java.util.List;
public class HomeActivity extends AppCompatActivity {
// Global variables \
DatabaseReference mRef;
List<PostModel> postList;
RecyclerView.Adapter recyclerAdapter;
RecyclerView recyclerView;
ProgressBar progressBar;
static String post_id;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
final DatabaseReference usersRef = FirebaseDatabase.getInstance().getReference("users");
final FirebaseAuth mAuth = FirebaseAuth.getInstance();
final FirebaseUser user = mAuth.getCurrentUser();
final ImageButton new_post = findViewById(R.id.new_post_btn);
final ImageButton settings = findViewById(R.id.settingsButton);
ImageButton like_btn = findViewById(R.id.likeBtn);
recyclerView = findViewById(R.id.recyclerView);
mRef = FirebaseDatabase.getInstance().getReference().child("posts");
progressBar = findViewById(R.id.progressBar4);
progressBar.setVisibility(View.VISIBLE);
postList = new ArrayList<>();
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
if (user == null) {
finish();
startActivity(new Intent(HomeActivity.this, MainActivity.class));
}
mRef.addListenerForSingleValueEvent(new ValueEventListener(){
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
PostModel post = new PostModel();
post_id = snapshot.child("id").getValue().toString();
post.setImgUrl(snapshot.child("imgUrl").getValue().toString());
post.setName(snapshot.child("name").getValue().toString());
post.setLikes(snapshot.child("likes").getValue().toString());
// check if post is liked from current user or not \
if (snapshot.child("likesList").exists()){
if (snapshot.child("likesList").child(user.getDisplayName()).exists()) {
// post is liked \
like_btn.setImageResource(R.drawable.like_emoji);
}
}else{
// post is not liked \
like_btn.setImageResource(R.drawable.like_emoji_before);
}
postList.add(post);
// notify adapter when a new item was added \
if (recyclerAdapter != null){
recyclerAdapter.notifyDataSetChanged();
}
}
progressBar.setVisibility(View.GONE);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError){
Toast.makeText(HomeActivity.this, "Error: " + databaseError, Toast.LENGTH_SHORT).show();
progressBar.setVisibility(View.GONE);
}
});
recyclerAdapter = new RecyclerAdapter(HomeActivity.this,postList);
recyclerView.setAdapter(recyclerAdapter);
recyclerAdapter.notifyDataSetChanged();
settings.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(HomeActivity.this, SettingsActivity.class));
}
});
new_post.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(HomeActivity.this, UploadPhotoActivity.class));
}
});
}
public void clearList(){
if (postList != null){
postList.clear();
if (recyclerAdapter != null){
recyclerAdapter.notifyDataSetChanged();
}
}
postList = new ArrayList<>();
}
}
注意:我使like_btn全局，但不再工作。
您的post_item.xml文件是否附加到回收站视图?如果是，则必须使用click listener。
从recyclerAdapter.java中访问您的按钮