NullPointerException at this.getReadableDatabase（）;

问题描述

嘿：）

我看过同一主题的几个问题，但没有找到解决问题的方法。

I looked at several Questions to the same topic, but I found no solution to my problem.

出现在 this.getReadableDatabase（）; 的NullPointerException ...

A NullPointerException at this.getReadableDatabase(); appears...

这是我的代码：

public class DatabaseHandler extends SQLiteOpenHelper {

public static final int DATABASE_VERSION = 1;

public static final String DATABASE_NAME = "TODO_APP";

/*--------------------------- TABLE ITEMS START ---------------------------*/
private static final String TABLE_ITEMS = "items";
private static String KEY_ID_ITEMS = "id_items";
private static final String KEY_CATEGORY_ITEMS = "category";
private static final String KEY_DATETIME_ITEMS = "datetime";
private static String KEY_NAME_ITEMS = "name";
private static final String KEY_DESCRIPTION_ITEMS = "description";
private static final String KEY_ALARM_ITEMS = "alarm";

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

@Override
public void onCreate(SQLiteDatabase db) {

    // create table ITEMS
    String CREATE_ITEMS_TABLE = "CREATE TABLE " + TABLE_ITEMS + "("
            + KEY_ID_ITEMS + " INTEGER PRIMARY KEY," + KEY_CATEGORY_ITEMS
            + " INTEGER," + KEY_DATETIME_ITEMS
            + " TIMESTAMP DEFAULT CURRENT_TIMESTAMP," + KEY_NAME_ITEMS
            + " TEXT," + KEY_DESCRIPTION_ITEMS + " TEXT," + KEY_ALARM_ITEMS
            + " INTEGER" + ");";
    db.execSQL(CREATE_ITEMS_TABLE);
}

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

    // Create tables again
    this.onCreate(db);
}

public void addItem(DB_Item item) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_CATEGORY_ITEMS, item.getCategory());
    values.put(KEY_NAME_ITEMS, item.getName());
    values.put(KEY_DESCRIPTION_ITEMS, item.getDescription());
    values.put(KEY_ALARM_ITEMS, item.getAlarm());

    // Inserting Row
    db.insert(TABLE_ITEMS, null, values);
    db.close(); // Closing database connection
}

public DB_Item getItem(String name) {

//!!!!! Here is one problem !!!!!
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_ITEMS, new String[] { KEY_ID_ITEMS,
            KEY_CATEGORY_ITEMS, KEY_DATETIME_ITEMS, KEY_NAME_ITEMS,
            KEY_DESCRIPTION_ITEMS, KEY_ALARM_ITEMS },
            KEY_NAME_ITEMS = " = ?", new String[] { String.valueOf(name) },
            null, null, null, null);
    if (cursor != null) {
        cursor.moveToFirst();
    }

    // DB_Item (int category, String name, String description, int
    // alarm)
    DB_Item item = new DB_Item(cursor.getInt(1), cursor.getString(3),
            cursor.getString(4), cursor.getInt(5));

    return item;
}

public List<DB_Item> getAllItems() {
    List<DB_Item> itemList = new ArrayList<DB_Item>();

    // SELECT ALL
    String selectQuery = "SELECT * FROM " + TABLE_ITEMS;

//!!!!!!!!!! here is the other Problem
    SQLiteDatabase database = this.getWritableDatabase();

    Cursor cursor = database.rawQuery(selectQuery, null);

    // go through all rows and then adding to list
    if (cursor.moveToFirst()) {
        do {
            DB_Item item = new DB_Item();
            item.setCategory(Integer.parseInt(cursor.getString(0)));
            // TODO

            // adding to list
            itemList.add(item);
        } while (cursor.moveToNext());
    }
    return itemList;
}

[依此类推，没有复制整个代码]

[and so on, didn't copy the whole code]

希望您能为我提供帮助...
该错误肯定出现在 SQLiteDatabase db = this.getReadableDatabase（）;

Hope you can help me...The error appears definitely at SQLiteDatabase db = this.getReadableDatabase();

输出：

09-03 08:34:17.863: E/AndroidRuntime(7074): java.lang.RuntimeException: Unable to start activity ComponentInfo{todo.todo_list/todo.view.StartApp}: java.lang.NullPointerException
09-03 08:34:17.863: E/AndroidRuntime(7074):     at todo.database.DatabaseHandler.getAllItems(DatabaseHandler.java:144)
09-03 08:34:17.863: E/AndroidRuntime(7074):     at todo.helper.SortItems.sortItemsCategory(SortItems.java:16)
09-03 08:34:17.863: E/AndroidRuntime(7074):     at todo.view.StartApp.onCreate(StartApp.java:36)

推荐答案

只需使用 getReadableDatabase（）而不使用此。

这篇关于NullPointerException at this.getReadableDatabase（）;的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！