我的 customAdapter 或 Activity.java 有什么问题？

Question

我正在开发 RecyclerView 并使用 CustomAdapter 并且我的应用程序运行顺利，但我的 ListView 没有显示它的内容！我的代码有什么遗漏或错误？我试图返回 arraylist.size() 并输入 list.setHasFixedSize 并没有工作！潜在所有者_listview.java（活动类）public class prospectowner_listview extends AppCompatActivity {    RecyclerView list;    ArrayList <com.example.android.e7gzlykora.owner> ownerlist = new ArrayList <>();    private DatabaseReference mFirebaseDatabase;    private FirebaseDatabase mFirebaseInstance;    owner owner;    customAdapter adapter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.prospectowner_listview);        list = findViewById(R.id.list);        LinearLayoutManager manager = new LinearLayoutManager(this);        list.setLayoutManager(manager);        list.setHasFixedSize(true);        manager.setOrientation(LinearLayoutManager.VERTICAL);        adapter = new customAdapter(prospectowner_listview.this,ownerlist);        mFirebaseInstance = FirebaseDatabase.getInstance();        mFirebaseDatabase = mFirebaseInstance.getReference("owners");        mFirebaseDatabase.addValueEventListener(new ValueEventListener() {            @Override            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {                for (DataSnapshot data: dataSnapshot.getChildren()){                    owner o = data.getValue(owner.class);                    ownerlist.add(o);                }                list.setAdapter(adapter);            }            @Override            public void onCancelled(@NonNull DatabaseError databaseError) { }        });    }}客户适配器.javapublic class customAdapter extends RecyclerView.Adapter<customAdapter.MyViewHolder>{    private final ArrayList<owner> ownerlist;    private final Context mContext;    public customAdapter(Context c , ArrayList<owner> p) {        this.mContext = c;        this.ownerlist = new ArrayList <>();    }

Answer 1

我认为问题来自您的适配器，请更改您的适配器代码，如下所示：

public class customAdapter extends RecyclerView.Adapter<customAdapter.MyViewHolder>{

    private ArrayList<owner> ownerlist;

    private Context mContext;

    public customAdapter(Context c , ArrayList<owner> p) {

        this.mContext = c;

        this.ownerlist = p;

    }

    @NonNull

    @Override

    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int 

    viewType) {

        return new MyViewHolder(LayoutInflater.from(mContext).inflate(R.layout.prospectowners,parent,false));

    }

    @Override

    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {

        owner owner = ownerlist.get(position);

        holder.name.setText(owner.getName());

        holder.field.setText(owner.getFieldname());

        holder.mobile.setText(owner.getMobile());

        holder.address.setText(owner.getAddress());

        holder.cost.setText(owner.getCost());

    }

    @Override

    public int getItemCount() {

        return ownerlist.size();

    }

    public void addData(ArrayList<owner> newData){

        this.ownerlist.addAll(newData);

        notifyOnDataSetChanged();

    }

    public class MyViewHolder extends RecyclerView.ViewHolder {

        public TextView name;

        public TextView field;

        public TextView mobile;

        public TextView address;

        public TextView cost;

       public MyViewHolder(View itemView) {

            super(itemView);

            this.name = itemView.findViewById(R.id.name);

            this.field =  itemView.findViewById(R.id.fieldName);

            this.mobile =  itemView.findViewById(R.id.mobileowner);

            this.address =  itemView.findViewById(R.id.address);

            this.cost =  itemView.findViewById(R.id.cost);

        }

    }

}

然后像这样调用方法addData：

@Override

            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                for (DataSnapshot data: dataSnapshot.getChildren()){

                    owner o = data.getValue(owner.class);

                    ownerlist.add(o);

                }

                list.setAdapter(adapter);

                adapter.addData(ownerlist);

            }

顺便说一句，实际上您可以在侦听器之外设置适配器

UPDATE（此更新设置适配器值的位置默认为空数据，然后在监听触发时填充）

public class customAdapter extends RecyclerView.Adapter<customAdapter.MyViewHolder>{

    private ArrayList<owner> ownerlist;

    private Context mContext;

    public customAdapter(Context c , ArrayList<owner> p) {

        this.mContext = c;

        this.ownerlist = new Arraylist<>();

    }

    @NonNull

    @Override

    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int 

    viewType) {

        return new MyViewHolder(LayoutInflater.from(mContext).inflate(R.layout.prospectowners,parent,false));

    }

    @Override

    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {

        owner owner = ownerlist.get(position);

        holder.name.setText(owner.getName());

        holder.field.setText(owner.getFieldname());

        holder.mobile.setText(owner.getMobile());

        holder.address.setText(owner.getAddress());

        holder.cost.setText(owner.getCost());

    }

    @Override

    public int getItemCount() {

        return ownerlist.size();

    }

    public void addData(ArrayList<owner> newData){

        this.ownerlist.addAll(newData);

        notifyOnDataSetChanged();

    }

    public class MyViewHolder extends RecyclerView.ViewHolder {

        public TextView name;

        public TextView field;

        public TextView mobile;

        public TextView address;

        public TextView cost;

       public MyViewHolder(View itemView) {

            super(itemView);

            this.name = itemView.findViewById(R.id.name);

            this.field =  itemView.findViewById(R.id.fieldName);

            this.mobile =  itemView.findViewById(R.id.mobileowner);

            this.address =  itemView.findViewById(R.id.address);

            this.cost =  itemView.findViewById(R.id.cost);

        }

    }

}

public class prospectowner_listview extends AppCompatActivity {

    RecyclerView list;

    ArrayList <com.example.android.e7gzlykora.owner> ownerlist = new ArrayList <>();

    private DatabaseReference mFirebaseDatabase;

    private FirebaseDatabase mFirebaseInstance;

    owner owner;

    customAdapter adapter;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.prospectowner_listview);

        list = findViewById(R.id.list);

        LinearLayoutManager manager = new LinearLayoutManager(this);

        list.setLayoutManager(manager);

        list.setHasFixedSize(true);

        manager.setOrientation(LinearLayoutManager.VERTICAL);

        adapter = new customAdapter(prospectowner_listview.this,ownerlist);

        list.setAdapter(adapter);

        mFirebaseInstance = FirebaseDatabase.getInstance();

        mFirebaseDatabase = mFirebaseInstance.getReference("owners");

        mFirebaseDatabase.addValueEventListener(new ValueEventListener() {

            @Override

            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                for (DataSnapshot data: dataSnapshot.getChildren()){

                    owner o = data.getValue(owner.class);

                    ownerlist.add(o);

                }

                adapter.addData(ownerlist);

            }

            @Override

            public void onCancelled(@NonNull DatabaseError databaseError) { }

        });

    }

}

Answer 2

在适配器中创建新功能：

public void addData(List<Owner> owners){

 this.ownerList = owners;

 notifyOnDataSetChanged();

}

并在onDataChange通话中：

adapter.addData(owners);

Answer 3

数组列表始终为空，因为您初始化为新列表的适配器构造函数。请检查一下

Answer 4

试试这个，

在您的活动课程中更改

list.setAdapter(adapter)

到

list.setAdapter(new customAdapter(prospectowner_listview.this, ownerlist));