在通过SQLite Manager更新了我的SQLite数据库列之后，为什么这些更改没有反映在我的Android应用程序

Question

我正在编写一个android应用程序，该应用程序使用SQLite数据库来存储有关书籍的信息（id、标题、作者和评级）。最终，目标是通过CRUD实现将该信息输出给用户。现在，我有一个类来建立Books的各种属性，一个SQLHelper类，一个用于最终列表视图的ListAdapter，当然还有一个MainActivity类来运行应用程序并实现所有内容。

我正在将前3列（id、title和author）的条目硬编码到DB中。之后，我将使用Firefox扩展SQLiteManager来更新"评级"列。然而，现在，我无法克服我一直在犯的错误；当我尝试运行该应用程序时，它会崩溃，而且我在SQLite Manager中所做的更改似乎没有反映在Logcat文件中（我使用导出DB文件，使用管理器编辑，然后导入回项目中）。

稍后我可以也将致力于应用程序、UI和其他美学因素的展示，现在我只想弄清楚为什么我的数据库更改没有得到反映。

Logcat的完整输出在这里，但我相信相关信息是：

11-16 19:32:07.777 2433-2433/? E/AndroidRuntime: FATAL EXCEPTION: main
11-16 19:32:07.777 2433-2433/? E/AndroidRuntime: Process: com.bookreviews.hernandez.bookreviews, PID: 2433
11-16 19:32:07.777 2433-2433/? E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.trim()' on a null object reference

从这一点我了解到错误在我的MainActivity.java中，但我还没有确定原因。

---

主要活动.java

package com.bookreviews.hernandez.bookreviews;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d("Name", "C H");
    SqlHelper db = new SqlHelper(this);
/** CRUD Operations **/
// add Books
    /*
    db.addBook(new Book("Professional Android 4 Application Development",
    "Reto Meier"));
    db.addBook(new Book("Beginning Android 4 Application Development", "Wei-Meng Lee"));
    db.addBook(new Book("Programming Android", "Wallace Jackson"));
    db.addBook(new Book("Hello, Android", "Wallace Jackson"));
    */
// get all books
    List<Book> list = db.getAllBooks();
// update one book
    int j = db.updateBook(list.get(0), "Hello, Android", "Ben Wallace");
// delete one book
// db.deleteBook(list.get(0));
// get all books
    db.getAllBooks();
    ListView listContent = (ListView) findViewById(R.id.list);
    List<Book> books = new ArrayList<Book>();
    books=db.getAllBooks();
//get data from the table by the ListAdapter
    ListAdapter customAdapter = new ListAdapter(this, R.layout.itemlistrow, books );
    listContent.setAdapter(customAdapter);
// get # of records
    db.getIds(list.get(0));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}
}

---

Book.java

package com.bookreviews.hernandez.bookreviews;
public class Book {
private int id;
private String title;
private String author;
private String rating;
public void setRating(String rating) {
    this.rating = rating;
}
public String getRating() {
    return rating;
}
public Book(){}
public Book(String title, String author) {
    super();
    this.title = title;
    this.author = author;
}
//getters & setters
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}
public String getAuthor() {
    return author;
}
public void setAuthor(String author) {
    this.author = author;
}
@Override
public String toString() {
    return "Book [id=" + id + ", title=" + title + ", author=" + author
            + ", rating=" + rating + "]";
}
}

---

SqlHelper.java

package com.bookreviews.hernandez.bookreviews;
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;
public class SqlHelper extends SQLiteOpenHelper {
// Database Version
private static final int DATABASE_VERSION = 6;
// Database Name
private static final String DATABASE_NAME = "BookDB";
// 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";
public SqlHelper(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, "+
            "rating 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) */
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
    // 4. Close dbase
    db.close();
}
// 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, 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(159) }); //selection args
// 4. close dbase
    db.close();
    Log.d("UpdateBook", book.toString());
    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());
}
public int getIds(Book book)
{
    String selectQuery = "SELECT id FROM books";
    SQLiteDatabase database = this.getReadableDatabase();
    Cursor c = database.rawQuery(selectQuery, null);
    c.moveToFirst();
    int total = c.getCount();
    Log.d("getIds", "Count=" + total);
    return total;
}
}

---

ListAdapter.java

package com.bookreviews.hernandez.bookreviews;
import java.util.List;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.RatingBar;
import android.widget.TextView;
public class ListAdapter extends ArrayAdapter<Book> {
private List<Book> items;
public ListAdapter(Context context, int textViewResourceId) {
    super(context, textViewResourceId);
}
public ListAdapter(Context context, int resource, List<Book> items) {
    super(context, resource, items);
    this.items = items;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View v = convertView;
    if (v == null) {
        LayoutInflater vi;
        vi = LayoutInflater.from(getContext());
        v = vi.inflate(R.layout.itemlistrow, null);
    }
    Book p = getItem(position);
    if (p != null) {
        TextView tt = (TextView) v.findViewById(R.id._id);
        TextView tt1 = (TextView) v.findViewById(R.id.title);
        TextView tt3 = (TextView) v.findViewById(R.id.author);
        RatingBar rb = (RatingBar) v.findViewById(R.id.rating);
        if (tt != null) {
            tt.setText("" + p.getId());
        }
        if (tt1 != null) {
            tt1.setText(p.getTitle());
        }
        if (tt3 != null) {
            tt3.setText(p.getAuthor());
        }
        if (rb != null) {
            float rating = Float.parseFloat(p.getRating());
            rb.setRating(rating);
        }
    }
    return v;
}
}

---

itemlistrow.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView android:textColor="#000"
    android:id="@+id/_id"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="id" android:textStyle="bold"
    android:gravity="left"
    android:layout_weight="1"
    android:typeface="monospace"
    android:height="40sp" />
<TextView android:textColor="#000"
    android:id="@+id/title"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="title"
    android:layout_weight="1"
    android:height="20sp" />
<TextView android:layout_height="wrap_content"
    android:layout_width="fill_parent"
    android:layout_weight="1"
    android:textColor="#000"
    android:gravity="right"
    android:id="@+id/author"
    android:text="author"
    android:height="20sp" />
<RatingBar
    android:id="@+id/rating"
    style="?android:attr/ratingBarStyleSmall"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:paddingTop="6dip"
    android:stepSize="0.25"
    android:numStars="5"
    />
</LinearLayout>

---

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:baselineAligned="false"
android:orientation="vertical" >
<ListView
    android:id="@+id/list"
    android:layout_width="250dp"
    android:layout_marginTop="10dp"
    android:layout_marginBottom="10dp"
    android:layout_height="fill_parent"
    android:layout_gravity="center" >
</ListView>
</LinearLayout>

显示数据库条目的Logcat。尽管我已经通过SQLite管理器更新了评级，但评级仍然显示为"null"。

19:32:07.426 2433-2433/? D/getAllBooks(): [Book [id=1, title=Professional Android 4 Application Development, author=Reto Meier, rating=null], Book [id=2, title=Beginning Android 4 Application Development, author=Wei-Meng Lee, rating=null], Book [id=3, title=Programming Android, author=Wallace Jackson, rating=null], Book [id=4, title=Hello, Android, author=Wallace Jackson, rating=null]]

问题：

我的SQLite Manager更改没有反映在Logcat中，应用程序崩溃

我已经尝试过的：

卸载和重新安装应用程序，升级数据库版本，删除数据库并通过启动

我正在使用的内容：

Android Studio 的最新版本

Firefox的SQLite Manager

对于如何解决这些错误并反映数据库更改的任何建议或建议，我们将不胜感激。

Answer 1

看起来您没有在SQLiteHelper类的getAllBooks()方法中设置评级。