Android 把查询的数据显示在页面上显示不出来，代码贴上麻烦大神指点一二

MainActivity 的代码package com.example.administrator.databasetest;import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;public class MainActivity extends AppCompatActivity {
    private MyDatabaseHelper dbHelper;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbHelper=new MyDatabaseHelper(this,"BookStore.db",null,2);
        Button createDatabase = (Button) findViewById(R.id.create_database);
        createDatabase.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                dbHelper.getWritableDatabase();
            }
        });
        Button addData = (Button)findViewById(R.id.add_data);
        addData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SQLiteDatabase db=dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("name","The Da Vinci Code");
                values.put("author","Dan Brown");
                values.put("pages",454);
                values.put("price",16.96);
                db.insert("Book",null,values);
                values.clear();
                values.put("name","The Lost Symbol");
                values.put("author","Dan Brown");
                values.put("pages",510);
                values.put("price",19.95);
                db.insert("Book",null,values);
            }
        });
        Button updataData = (Button) findViewById(R.id.update_data);
        updataData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("price",10.5);
                db.update("Book",values,"name = ?",new String[]{"The Da Vinci Code"});
            }
        });        Button deleteButton = (Button) findViewById(R.id.delete_data);
        deleteButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                db.delete("Book","pages > ?",new String[]{"500"});
            }
        });
        Button queryButton = (Button) findViewById(R.id.query_data);
        queryButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                Cursor cursor = db.query("Book",null,null,null,null,null,null);
                if (cursor.moveToFirst()){
                    do {
                        String name = cursor.getString(cursor.getColumnIndex("name"));
                        String author = cursor.getString(cursor.getColumnIndex("author"));
                        int pages = cursor.getInt(cursor.getColumnIndex("pages"));
                        double price = cursor.getDouble(cursor.getColumnIndex("price"));
                        TextView mz = (TextView)findViewById(R.id.mz);
                        mz.setText("书名"+name);
                        TextView zz = (TextView)findViewById(R.id.zz);
                        zz.setText("作者"+author);
                        TextView ys = (TextView)findViewById(R.id.ys);
                        ys.setText("页数"+pages);
                        TextView jg =(TextView)findViewById(R.id.jg);
                        jg.setText("价格"+price);                    }while (cursor.moveToNext());
                }cursor.close();
            }
        });    }
}MyDatabaseHelper 的代码package com.example.administrator.databasetest;import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Toast;/**
 * Created by Administrator on 2019/6/14.
 */public class MyDatabaseHelper extends SQLiteOpenHelper {
    public static final String CREATE_BOOK = "create table Book ("
            +"id integer primary key autoincrement,"
            +"author text,"
            +"price real,"
            +"pages integer,"
            +"name text)";
     public static final String CREATE_CATEGORY = "create table Category("
             +"id integer primary key autoincrement,"
             +"category_name text,"
             +"category_code integer)";
    private Context mContext;
    public MyDatabaseHelper (Context context, String name, SQLiteDatabase.CursorFactory factory,int version)
    {
        super(context,name,factory,version);
        mContext=context;
    }
    @Override
    public void onCreate(SQLiteDatabase db){
        db.execSQL(CREATE_BOOK);
        db.execSQL(CREATE_CATEGORY);
        Toast.makeText(mContext,"创建成功",Toast.LENGTH_SHORT).show();
    }
    @Override
    public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion){
        db.execSQL("drop table if exists Book");
        db.execSQL("drop table if exists Category");
        onCreate(db);
    }
}activity_main.xml 布局的代码<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
<Button
       android:id="@+id/create_database"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
        android:text="添加数据库"/>
      <Button
          android:id="@+id/add_data"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:text="添加默认数据"/>
    <Button
        android:id="@+id/update_data"
        android:text="添加数据"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/delete_data"
        android:text="删除"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/query_data"
        android:text="查询"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/mz"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/zz"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/ys"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/jg"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>
运行之后点击查询为什么查询不出来呢，是哪里用错了