Question

我正在尝试创建一个群组活动，在该活动中可以显示用户连接到的所有群组。我已经创建了分组活动，并在其中插入了回收站视图，并试图从数据库中检索数据，但是不幸的是，当我在Android手机上运行应用程序时出现错误。应用程序崩溃了，并且在logcat中，我收到一条消息，提示无法将java.lang.String类型的对象转换为com.nanb.alpha.modelclass类型。如果您不介意，请帮助我，以便我完成活动。

下面的代码是用户可以创建组的代码。

      private void groupmethos(final String groupname) {
    DatabaseReference groupref = rootref.child("Group").push();
    final String grouppushid = groupref.getKey();
    Map groupmap = new HashMap<>();
    groupmap.put("GroupprofileName",groupname);
    groupmap.put("Creater",currentUser.getUid());
    groupmap.put("StatusGroup","");
    groupmap.put("profileimage","");
    groupmap.put("id",grouppushid);
    rootref.child("Group").child(grouppushid).updateChildren(groupmap).addOnCompleteListener(new OnCompleteListener() {
        @Override
        public void onComplete(@NonNull Task task) {
            rootref.child("GroupMessage").child(grouppushid).setValue("").addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    if (task.isSuccessful()){
                        rootref.child("userconnectedtogroup").child(currentUser.getUid()).child(grouppushid).setValue("Added").addOnCompleteListener(new OnCompleteListener<Void>() {
                            @Override
                            public void onComplete(@NonNull Task<Void> task) {
                                Toast.makeText(MainActivity.this,groupname + "group Created successfully",Toast.LENGTH_SHORT).show();
                            }
                        });

                    }
                }
            });

        }
    });
  }

在上述代码中，

用户请求创建一个组。下面给出的是使用getter和setter从数据库中获取数据的代码。

  package com.nanb.alpha;

public class modelclass {
private String GroupprofileName,StatusGroup,profileimage;

public modelclass() {
}

public modelclass(String groupprofileName, String statusGroup, String profileimage) {
    this.GroupprofileName = groupprofileName;
    this.StatusGroup = statusGroup;
    this.profileimage = profileimage;
}

public String getGroupprofileName() {
    return GroupprofileName;
}

public void setGroupprofileName(String groupprofileName) {
    GroupprofileName = groupprofileName;
}

public String getStatusGroup() {
    return StatusGroup;
}

public void setStatusGroup(String statusGroup) {
    StatusGroup = statusGroup;
}

public String getProfileimage() {
    return profileimage;
}

public void setProfileimage(String profileimage) {
    this.profileimage = profileimage;
}
}

给定代码是recyclerview用来将值设置为给定布局的代码。

     public class group extends AppCompatActivity {

     private RecyclerView recyclerView;
     private DatabaseReference conref,groupref;
     private FirebaseAuth mAuth;
     private String Currentuserid;


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

    intialiation();
    mAuth = FirebaseAuth.getInstance();
    Currentuserid = mAuth.getCurrentUser().getUid();
    conref = FirebaseDatabase.getInstance().getReference().child("userconnectedtogroup").child(Currentuserid);
    groupref = FirebaseDatabase.getInstance().getReference().child("Group");
    }

    private void intialiation() {
    recyclerView = findViewById(R.id.recyclerview);
    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(layoutManager);
    }

     @Override
     protected void onStart() {
    super.onStart();
    FirebaseRecyclerOptions option = new FirebaseRecyclerOptions.Builder<modelclass>().setQuery(conref,modelclass.class).build();

    FirebaseRecyclerAdapter<modelclass,group_viewHolder> adapter = new FirebaseRecyclerAdapter<modelclass, group_viewHolder>(option) {
        @Override
        protected void onBindViewHolder(@NonNull final group_viewHolder group_viewHolder, int i, @NonNull modelclass modelclass) {
            String userid = getRef(i).getKey();
            groupref.child(userid).addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                  if(dataSnapshot.hasChild("profileimage")){
                      String profileimage = dataSnapshot.child("profileimage").getValue().toString();
                      String groupname = dataSnapshot.child("GroupprofileName").getValue().toString();
                      String groupStatus = dataSnapshot.child("StatusGroup").getValue().toString();

                      group_viewHolder.groupname.setText(groupname);
                      group_viewHolder.groupStatus.setText(groupStatus);
                      Picasso.get().load(profileimage).into(group_viewHolder.profileimage);
                  }else{
                      String groupname = dataSnapshot.child("GroupprofileName").getValue().toString();
                      String groupStatus = dataSnapshot.child("StatusGroup").getValue().toString();

                      group_viewHolder.groupname.setText(groupname);
                      group_viewHolder.groupStatus.setText(groupStatus);
                      Picasso.get().load(R.mipmap.groupicon).into(group_viewHolder.profileimage);
                  }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        @NonNull
        @Override
        public group_viewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
           View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.grouplayout,parent,false);
           group_viewHolder groupholder = new group_viewHolder(view);
            return groupholder;
        }
    };
    recyclerView.setAdapter(adapter);
    adapter.startListening();
    }

    public static class group_viewHolder extends RecyclerView.ViewHolder{
    TextView groupname,groupStatus;
    CircleImageView profileimage;
    public group_viewHolder(@NonNull View itemView) {
        super(itemView);
        groupname = itemView.findViewById(R.id.Group_name);
        groupStatus = itemView.findViewById(R.id.Group_Status);
        profileimage = itemView.findViewById(R.id.group_profile_dp);
    }
    }
    }

以下是我的Firebase数据库的图像。其中显示了与小组活动有关的所有结构。

下面是在应用程序崩溃后显示的logcat消息。

com.google.firebase.database.DatabaseException：无法将java.lang.String类型的对象转换为com.nanb.alpha.modelclass类型在com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean（com.google.firebase：firebase-database @@ 19.1.0：418） com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass（com.google.firebase：firebase-database @@ 19.1.0：214） com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass（com.google.firebase：firebase-database @@ 19.1.0：79） com.google.firebase.database.DataSnapshot.getValue（com.google.firebase：firebase-database @@ 19.1.0：203）在com.firebase.ui.database.ClassSnapshotParser.parseSnapshot（ClassSnapshotParser.java:29）在com.firebase.ui.database.ClassSnapshotParser.parseSnapshot（ClassSnapshotParser.java:15）在com.firebase.ui.common.BaseCachingSnapshotParser.parseSnapshot（BaseCachingSnapshotParser.java:35）在com.firebase.ui.common.BaseObservableSnapshotArray.get（BaseObservableSnapshotArray.java:52）在com.firebase.ui.database.FirebaseRecyclerAdapter.getItem（FirebaseRecyclerAdapter.java:106）在com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder（FirebaseRecyclerAdapter.java:122）在androidx.recyclerview.widget.RecyclerView $ Adapter.onBindViewHolder（RecyclerView.java:6781）在androidx.recyclerview.widget.RecyclerView $ Adapter.bindViewHolder（RecyclerView.java:6823）在androidx.recyclerview.widget.RecyclerView $ Recycler.tryBindViewHolderByDeadline（RecyclerView.java:5752）在androidx.recyclerview.widget.RecyclerView $ Recycler.tryGetViewHolderForPositionByDeadline（RecyclerView.java:6019）在androidx.recyclerview.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5858）在androidx.recyclerview.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5854）在androidx.recyclerview.widget.LinearLayoutManager $ LayoutState.next（LinearLayoutManager.java:2230）在androidx.recyclerview.widget.LinearLayoutManager.layoutChunk（LinearLayoutManager.java:1557）在androidx.recyclerview.widget.LinearLayoutManager.fill（LinearLayoutManager.java:1517）在androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren（LinearLayoutManager.java:612）在androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2（RecyclerView.java:3924）在androidx.recyclerview.widget.RecyclerView.dispatchLayout（RecyclerView.java:3641）在androidx.recyclerview.widget.RecyclerView.onLayout（RecyclerView.java:4194）在android.view.View.layout（View.java:15689）在android.view.ViewGroup.layout（ViewGroup.java:5048）在androidx.constraintlayout.widget.ConstraintLayout.onLayout（ConstraintLayout.java:1915）在android.view.View.layout（View.java:15689）在android.view.ViewGroup.layout（ViewGroup.java:5048）在android.widget.FrameLayout.layoutChildren（FrameLayout.java:579）在android.widget.FrameLayout.onLayout（FrameLayout.java:514）在android.view.View.layout（View.java:15689）在android.view.ViewGroup.layout（ViewGroup.java:5048）在android.widget.LinearLayout.setChildFrame（LinearLayout.java:1703）在android.widget.LinearLayout.layoutVertical（LinearLayout.java:1557）在android.widget.LinearLayout.onLayout（LinearLayout.java:1466）在android.view.View.layout（View.java:15689）在android.view.ViewGroup.layout（ViewGroup.java:5048）在android.widget.FrameLayout.layoutChildren（FrameLayout.java:579）在android.widget.FrameLayout.onLayout（FrameLayout.java:514）在android.view.View.layout（View.java:15689）在android.view.ViewGroup.layout（ViewGroup.java:5048）在android.widget.LinearLayout.setChildFrame（LinearLayout.java:1703）在android.widget.LinearLayout.layoutVertical（LinearLayout.java:1557）在android.widget.LinearLayout.onLayout（LinearLayout.java:1466）在android.view.View.layout（View.java:15689）在android.view.ViewGroup.layout（ViewGroup.java:5048）在android.widget.FrameLayout.layoutChildren（FrameLayout.java:579）在android.widget.FrameLayout.onLayout（FrameLayout.java:514）在android

Answer 1

您在数据库中的userconnectedtogroup不包含模型，它包含诸如 Added 之类的字符串。如下更新您的query：

FirebaseRecyclerOptions option = new FirebaseRecyclerOptions.Builder<String>().setQuery(conref,String.class).build();
FirebaseRecyclerAdapter<String,group_viewHolder> adapter = new FirebaseRecyclerAdapter<String, group_viewHolder>(option) {
    @Override
    protected void onBindViewHolder(@NonNull final group_viewHolder group_viewHolder, int i, @NonNull modelclass modelclass) {
        String groupId = getRef(i).getKey();
        groupref.child(groupId).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                if(dataSnapshot.hasChild("profileimage")){
                    String profileimage = dataSnapshot.child("profileimage").getValue().toString();
                    String groupname = dataSnapshot.child("GroupprofileName").getValue().toString();
                    String groupStatus = dataSnapshot.child("StatusGroup").getValue().toString();

                    group_viewHolder.groupname.setText(groupname);
                    group_viewHolder.groupStatus.setText(groupStatus);
                    Picasso.get().load(profileimage).into(group_viewHolder.profileimage);
                }else{
                    String groupname = dataSnapshot.child("GroupprofileName").getValue().toString();
                    String groupStatus = dataSnapshot.child("StatusGroup").getValue().toString();

                    group_viewHolder.groupname.setText(groupname);
                    group_viewHolder.groupStatus.setText(groupStatus);
                    Picasso.get().load(R.mipmap.groupicon).into(group_viewHolder.profileimage);
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }

    @NonNull
    @Override
    public group_viewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.grouplayout,parent,false);
        group_viewHolder groupholder = new group_viewHolder(view);
        return groupholder;
    }
};

您还可以在onDataChange内部使用模型，如下所示：

@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

    modelclass modelClass = dataSnapshot.getValue(modelclass.class);

    if(!TextUtils.isEmpty(modelClass.getProfileimage())) {
        group_viewHolder.groupname.setText(modelClass.getGroupprofileName());
        group_viewHolder.groupStatus.setText(modelClass.getStatusGroup());
        Picasso.get().load(modelClass.getProfileimage()).into(group_viewHolder.profileimage);
    } else {
        group_viewHolder.groupname.setText(modelClass.getGroupprofileName());
        group_viewHolder.groupStatus.setText(modelClass.getStatusGroup());
        Picasso.get().load(R.mipmap.groupicon).into(group_viewHolder.profileimage);
    }
}

Answer 2

在选项对象中使用groupref而不是conref

我正在尝试使用getter和setter从我的Firebase数据库中检索数据，但收到错误消息说无法转换对象

2 个答案: