Отображение базы данных в Listview

Question

Я пытаюсь создать ListView, который отображает содержимое моей базы данных для активности в приложении Android. Метод, который я попытался сбой приложения перед его запуском. Ниже приведен мой код для моей основной деятельности и класса sqlhelper. Если бы кто-нибудь мог сказать мне, почему это было бы большой благодарностью.

Основная деятельность package com.mcclure.hannah.books;

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 

import java.util.List; 
import com.mcclure.hannah.books.MySQLiteHelper; 
import com.mcclure.hannah.books.Book; 
import android.os.Bundle; 
import android.app.Activity; 
import android.util.Log; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 

public class MainActivity extends Activity { 
private ListView lv ; 
private String TAG="Hannah"; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    lv=(ListView) findViewById(R.id.lv); 
    MySQLiteHelper db = new MySQLiteHelper(this); 

    /** 
    * CRUD Operations 
    * */ 
    // add Books 
    db.addBook(new Book("Android Application Development Cookbook", "Wei Meng Lee")); 
    db.addBook(new Book("Android Programming: The Big Nerd Ranch Guide", "Bill Phillips and Brian Hardy")); 
    db.addBook(new Book("Learn Android App Development", "Wallace Jackson")); 

    // get all books 
    List<Book> list = db.getAllBooks(); 

    // delete one book 
    db.deleteBook(list.get(0)); 

    // get all books 
    db.getAllBooks(); 

    String[] array = list.toArray(new String[list.size()]); 


    ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(
      this, 
      android.R.layout.simple_list_item_1, array); 
    Log.d(TAG,"**************************"); 
    lv.setAdapter(arrayAdapter); 



} 

}

MySQLiteHelper Classs

package com.mcclure.hannah.books; 
import java.util.LinkedList; 
import java.util.List; 
import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.util.Log; 
import com.mcclure.hannah.books.Book; 
public class MySQLiteHelper extends SQLiteOpenHelper { 

// Database Version 
private static final int DATABASE_VERSION = 1; 
// Database Name 
private static final String DATABASE_NAME = "BookDB"; 

public MySQLiteHelper(Context context) { 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    // SQL statement to create book table 
    String CREATE_BOOK_TABLE = "CREATE TABLE books (" + 
      "id INTEGER PRIMARY KEY AUTOINCREMENT, " + 
      "title TEXT, "+ 
      "author TEXT)"; 

    // create books table 
    db.execSQL(CREATE_BOOK_TABLE); 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    // Drop older books table if existed 
    db.execSQL("DROP TABLE IF EXISTS books"); 

    // create fresh books table 
    this.onCreate(db); 
} 
//--------------------------------------------------------------------- 

/** 
* CRUD operations (create "add", read "get", update, delete) book + get all books + delete all books 
*/ 

// Books table name 
private static final String TABLE_BOOKS = "books"; 

// Books Table Columns names 
private static final String KEY_ID = "id"; 
private static final String KEY_TITLE = "title"; 
private static final String KEY_AUTHOR = "author"; 

private static final String[] COLUMNS = {KEY_ID,KEY_TITLE,KEY_AUTHOR}; 

public void addBook(Book book){ 
    Log.d("addBook", book.toString()); 
    // 1. get reference to writable DB 
    SQLiteDatabase db = this.getWritableDatabase(); 

    // 2. create ContentValues to add key "column"/value 
    ContentValues values = new ContentValues(); 
    values.put(KEY_TITLE, book.getTitle()); // get title 
    values.put(KEY_AUTHOR, book.getAuthor()); // get author 

    // 3. insert 
    db.insert(TABLE_BOOKS, // table 
      null, //nullColumnHack 
      values); // key/value -> keys = column names/ values = column values 

    // 4. close 
    db.close(); 
} 

public Book getBook(int id){ 

    // 1. get reference to readable DB 
    SQLiteDatabase db = this.getReadableDatabase(); 

    // 2. build query 
    Cursor cursor = 
      db.query(TABLE_BOOKS, // a. table 
        COLUMNS, // b. column names 
        " id = ?", // c. selections 
        new String[] { String.valueOf(id) }, // d. selections args 
        null, // e. group by 
        null, // f. having 
        null, // g. order by 
        null); // h. limit 

    // 3. if we got results get the first one 
    if (cursor != null) 
     cursor.moveToFirst(); 

    // 4. build book object 
    Book book = new Book(); 
    book.setId(Integer.parseInt(cursor.getString(0))); 
    book.setTitle(cursor.getString(1)); 
    book.setAuthor(cursor.getString(2)); 

    Log.d("getBook("+id+")", book.toString()); 

    // 5. return book 
    return book; 
} 

// Get All Books 
public List<Book> getAllBooks() { 
    List<Book> books = new LinkedList<Book>(); 

    // 1. build the query 
    String query = "SELECT * FROM " + TABLE_BOOKS; 

    // 2. get reference to writable DB 
    SQLiteDatabase db = this.getWritableDatabase(); 
    Cursor cursor = db.rawQuery(query, null); 

    // 3. go over each row, build book and add it to list 
    Book book = null; 
    if (cursor.moveToFirst()) { 
     do { 
      book = new Book(); 
      book.setId(Integer.parseInt(cursor.getString(0))); 
      book.setTitle(cursor.getString(1)); 
      book.setAuthor(cursor.getString(2)); 

      // Add book to books 
      books.add(book); 
     } while (cursor.moveToNext()); 
    } 

    Log.d("getAllBooks()", books.toString()); 

    // return books 
    return books; 
} 

// Updating single book 
public int updateBook(Book book) { 

    // 1. get reference to writable DB 
    SQLiteDatabase db = this.getWritableDatabase(); 

    // 2. create ContentValues to add key "column"/value 
    ContentValues values = new ContentValues(); 
    values.put("title", book.getTitle()); // get title 
    values.put("author", book.getAuthor()); // get author 

    // 3. updating row 
    int i = db.update(TABLE_BOOKS, //table 
      values, // column/value 
      KEY_ID+" = ?", // selections 
      new String[] { String.valueOf(book.getId()) }); //selection args 

    // 4. close 
    db.close(); 

    return i; 

} 

// Deleting single book 
public void deleteBook(Book book) { 

    // 1. get reference to writable DB 
    SQLiteDatabase db = this.getWritableDatabase(); 

    // 2. delete 
    db.delete(TABLE_BOOKS, 
      KEY_ID+" = ?", 
      new String[] { String.valueOf(book.getId()) }); 

    // 3. close 
    db.close(); 

    Log.d("deleteBook", book.toString()); 

} 

сообщение об ошибке (StackTrace) отображаемая является:

04-21 16:12:09.364 6896-6896/com.mcclure.hannah.books E/AndroidRuntime: FATAL EXCEPTION: main 
    Process: com.mcclure.hannah.books, PID: 6896 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mcclure.hannah.books/com.mcclure.hannah.books.MainActivity}: java.lang.ArrayStoreException: com.mcclure.hannah.books.Book cannot be stored in an array of type java.lang.String[] 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2808) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2873) 
     at android.app.ActivityThread.access$900(ActivityThread.java:181) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1482) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:145) 
     at android.app.ActivityThread.main(ActivityThread.java:6145) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 
    Caused by: java.lang.ArrayStoreException: com.mcclure.hannah.books.Book cannot be stored in an array of type java.lang.String[] 
     at java.util.LinkedList.toArray(LinkedList.java:958) 
     at com.mcclure.hannah.books.MainActivity.onCreate(MainActivity.java:43) 
     at android.app.Activity.performCreate(Activity.java:6374) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2752) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2873)  
     at android.app.ActivityThread.access$900(ActivityThread.java:181)  
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1482)  
     at android.os.Handler.dispatchMessage(Handler.java:102)  
     at android.os.Looper.loop(Looper.java:145)  
     at android.app.ActivityThread.main(ActivityThread.java:6145)  
     at java.lang.reflect.Method.invoke(Native Method)  
     at java.lang.reflect.Method.invoke(Method.java:372)  
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)  
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)  

Answer 1

Вы пытаетесь добавить книгу в список строки:

String[] array = list.toArray(new String[list.size()]);