Android 适配器无法用视图填充活动

Question

在我的 MainActivity 中，我使用 RecyclerView 用图像和名称填充 Activity，但是当我运行应用程序时，Activity 是空的。一个适配器被称为填充了包含“id”的数据对象数组。适配器膨胀 item_view 并使用 ViewHolder 来保存文本视图并充当 onClickListener。

关于为什么它仍然是空的以及如何填充它的任何想法？

主活动：

package com.com.com;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;

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

public class MainActivity extends AppCompatActivity {

    private RecyclerView mRecyclerView;
    private RecyclerView.Adapter mDataAdapter;
    private RecyclerView.LayoutManager mDataLayoutManager;

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

        mRecyclerView = (RecyclerView)  findViewById(R.id.recyclerView);
        mRecyclerView.setNestedScrollingEnabled(false);
        mRecyclerView.setHasFixedSize(true);
        mMatchesLayoutManager = new LinearLayoutManager(MainActivity.this);
        mRecyclerView.setLayoutManager(mDataLayoutManager);
        mDataAdapter = new DataAdapter(getDataSetData(), MainActivity.this);
        mRecyclerView.setAdapter(mDataAdapter);

        for (int i = 0; i < 10; i++) {
            DataObject obj = new DataObject(Integer.toString(i));
            resultsData.add(obj);
        }
        mDataAdapter.notifyDataSetChanged();
    }

    private ArrayList<DataObject> resultsData = new ArrayList<DataObject>();
    private List<DataObject> getDataSetData() {
        return resultsData;
    }
}

数据适配器：

package com.com.com;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class DataAdapter extends RecyclerView.Adapter<DataViewHolders>{

    private List<DataObject> dataList;
    private Context context;

    public DataAdapter(List<DataObject> dataList, Context context) {
        this.dataList = dataList;
        this.context = context;
    }

    @Override
    public DataViewHolders onCreateViewHolder(ViewGroup parent, int viewType) {

        View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_data, null, false);
        RecyclerView.LayoutParams lp = new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
        layoutView.setLayoutParams(lp);
        DataViewHolders rcv = new DataViewHolders((layoutView));

        return rcv;
    }

    @Override
    public void onBindViewHolder(DataViewHolders holder, int position) {
        holder.mDataId.setText(dataList.get(position).getId());

    }

    @Override
    public int getItemCount() {
        return 0;
    }
}

数据对象：

package com.com.com;

public class DataObject {
    private String Id;

    public DataObject (String Id) {
        this.Id= Id;
    }

    public String getId() {
        return Id;
    }

    public void setId(String Id) {
        this.Id= Id;
    }

}

DataViewHolders：

package com.com.com;

import android.view.View;
import android.widget.TextView;

import androidx.recyclerview.widget.RecyclerView;

public class DatasViewHolders extends RecyclerView.ViewHolder implements View.OnClickListener {

    public TextView mDataId;

    public DataViewHolders(View itemView) {
        super(itemView);
        itemView.setOnClickListener(this);

        mDataId = (TextView) itemView.findViewById(R.id.Dataid);
    }

    @Override
    public void onClick(View v) {

    }
}

activity_main：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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=".MainActivity"
    android:orientation="vertical">

    <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.recyclerview.widget.RecyclerView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/recyclerView"
            android:scrollbars="vertical">

        </androidx.recyclerview.widget.RecyclerView>
    </androidx.core.widget.NestedScrollView>

</LinearLayout>

item_data：

<?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"
    android:orientation="horizontal"
    android:padding="20sp">

    <ImageView
        android:layout_width="75sp"
        android:layout_height="75sp"
        android:src="@mipmap/ic_launcher" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Data ID"
        android:layout_gravity="center"
        android:id="@+id/Dataid" />

</LinearLayout>

Answer 1

@Override
public int getItemCount() {
  return 0;
}

这里返回的值不对，一定是列表的大小。