Logcat顯示數據庫條目爲空值

Question

我從一個網站得到了下面的代碼，我也做了一些修改。當我在日誌貓中打印數據庫時，我得到了ID，但是我得到了作者和標題爲null.Can someone請告訴可能是什麼錯誤？

這是Book.java

package com.hmkcode.android.model; 
public class Book { 
private int id; 
private String title; 
private String author; 

public Book(){} 

public Book(String title, String author) { 
    super(); 
    this.title = title; 
    this.author = author; 
} 

//getters & setters 
// getting ID 
public int getId(){ 
    return this.id; 
} 

// setting id 
public void setId(int id){ 
    this.id = id; 
} 
// getting title 
public String getTitle(){ 
    return this.title; 
} 

// setting title 
public void setTitle(String name){ 
    this.title = title; 
} 

// getting authorname 
public String getAuthor(){ 
    return this.author; 
} 

// setting authorname 
public void setAuthor(String phone_number){ 
    this.author = author; 
} 
} 

這是MySQLiteHelper.java

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){ 
    // 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)); 
    // 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()); 
    } 
    // 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(); 
} 
} 

這是MainActivity.java

public class MainActivity extends Activity { 

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

    /** 
    * CRUD Operations 
    * */ 
    // add Books 
    /*Log.d("Inserting: ", "Inserting all 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"));*/ 
    //Reading and getting all books 
    Log.d("Reading: ", "Reading all Books.."); 
    List<Book> list = db.getAllBooks(); 
    for (Book cn:list) { 
     String log = "Id: "+cn.getId()+" ,Title: " + cn.getTitle() + " ,Author: " + cn.getAuthor(); 
      // Writing Contacts to log 
    Log.d("Name: ", log); 
    // delete one book 
    //db.deleteBook(list.get(3)); 
} 
} 
} 

，這就是我在logcat的

得到

12-17 12:18:01.498: D/Name:(506): Id: 29 ,Title: null ,Author: null 
12-17 12:18:01.498: D/Name:(506): Id: 33 ,Title: null ,Author: null 
12-17 12:18:01.498: D/Name:(506): Id: 36 ,Title: null ,Author: null 
12-17 12:18:01.498: D/Name:(506): Id: 41 ,Title: null ,Author: null 
12-17 12:18:01.498: D/Name:(506): Id: 42 ,Title: null ,Author: null 
12-17 12:18:01.498: D/Name:(506): Id: 43 ,Title: null ,Author: null 
12-17 12:18:01.498: D/Name:(506): Id: 44 ,Title: null ,Author: null 
12-17 12:18:01.508: D/Name:(506): Id: 45 ,Title: null ,Author: null 
12-17 12:18:01.508: D/Name:(506): Id: 46 ,Title: null ,Author: null 

忽略該ID沒有按順序，因爲我已刪除並添加了許多條目。

Answer 1

錯誤在你Book.java，

// setting title 
public void setTitle(String name){ ---> change argument as title you are using name 
    this.title = title; 
} 


// setting authorname 
public void setAuthor(String phone_number){ ---> change argument as author 
    this.author = author; 
} 
} 

FOR UPDATE：

// Updating single book 
public int updateBook(Book book, String newTitle, String newAuthor) { 

    // 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", newTitle); // get title 
    values.put("author", newAuthor()); // 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 

    // Based on your condition 

    // 4. close 
    db.close(); 

    return i; 

}