[英]using SQLite database for the very first time in android. how?
安装 android SDK 和 Eclipse 后,我第一次使用 SQLite。 我是否需要在 manifest.xml 中进行一些设置或注册?
我无法使用 SQLite 数据库,因为它显示如下错误
SQLite 数据库数据库; 红色下划线中的 SQLite 并声明为
(此行有多个标记 - SQLite 无法解析为类型 - 标记“SQLite”上的语法错误,修饰符无效)
并且
SQLite 无法解析为一种类型并给出建议:
创建类 sqlite 创建接口 sqlite 和其他 9 条建议。
我该做什么?
您需要有一个 databasehelper 类,这将使您易于理解。 您可以根据需要对其进行操作。
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DatabaseHandler {
public static final String KEY_ROWID = "_id";
public static final String KEY_PRONAME = "proname";
public static final String KEY_PROCOST = "procost";
private static final String TAG = "DBAdapter";
//private static final String TAG = DBAdapter.class.getSimpleName();
private static final String DATABASE_NAME = "product";
private static final String DATABASE_TABLE = "productdet";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE =
"create table productdet (_id integer primary key autoincrement, "+ "proname varchar ,"+ "procost varchar);";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DatabaseHandler(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
Log.w(TAG, "Upgrading database from version " + oldVersion
+ " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS productdet");
onCreate(db);
}
}
//---opens the database---
public DatabaseHandler open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
//---insert a title into the database---
public long insertTitle(String proname, String procost)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_PRONAME, proname);
initialValues.put(KEY_PROCOST, procost);
return db.insert(DATABASE_TABLE, null, initialValues);
}
//---deletes a particular title---
public boolean deleteTitle(long rowId)
{
return db.delete(DATABASE_TABLE, KEY_ROWID +
"=" + rowId, null) > 0;
}
//---retrieves all the titles---
public Cursor getAllTitles()
{
return db.query( DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_PRONAME,
KEY_PROCOST,
},
null,
null,
null, null, null);
}
//---retrieves a particular title---
public Cursor getTitle(long rowId) throws SQLException
{
Cursor mCursor =
db.query(true, DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_PRONAME,
KEY_PROCOST,
},
KEY_ROWID + "=" + rowId,
null,
null,
null, null, null
);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//---updates a title---
public boolean updateTitle(long rowId, String proname,
String procost)
{
ContentValues args = new ContentValues();
args.put(KEY_PRONAME, proname);
args.put(KEY_PROCOST, procost);
return db.update(DATABASE_TABLE, args,
KEY_ROWID + "=" + rowId, null) > 0;
}
}
这是一个很好的例子
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 PersonDatabaseHelper {
private static final String TAG = PersonDatabaseHelper.class.getSimpleName();
// database configuration
// if you want the onUpgrade to run then change the database_version
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "mydatabase.db";
// table configuration
private static final String TABLE_NAME = "person_table"; // Table name
private static final String PERSON_TABLE_COLUMN_ID = "_id"; // a column named "_id" is required for cursor
private static final String PERSON_TABLE_COLUMN_NAME = "person_name";
private static final String PERSON_TABLE_COLUMN_PIN = "person_pin";
private DatabaseOpenHelper openHelper;
private SQLiteDatabase database;
// this is a wrapper class. that means, from outside world, anyone will communicate with PersonDatabaseHelper,
// but under the hood actually DatabaseOpenHelper class will perform database CRUD operations
public PersonDatabaseHelper(Context aContext) {
openHelper = new DatabaseOpenHelper(aContext);
database = openHelper.getWritableDatabase();
}
public void insertData (String aPersonName, String aPersonPin) {
// we are using ContentValues to avoid sql format errors
ContentValues contentValues = new ContentValues();
contentValues.put(PERSON_TABLE_COLUMN_NAME, aPersonName);
contentValues.put(PERSON_TABLE_COLUMN_PIN, aPersonPin);
database.insert(TABLE_NAME, null, contentValues);
}
public Cursor getAllData () {
String buildSQL = "SELECT * FROM " + TABLE_NAME;
Log.d(TAG, "getAllData SQL: " + buildSQL);
return database.rawQuery(buildSQL, null);
}
// this DatabaseOpenHelper class will actually be used to perform database related operation
private class DatabaseOpenHelper extends SQLiteOpenHelper {
public DatabaseOpenHelper(Context aContext) {
super(aContext, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
// Create your tables here
String buildSQL = "CREATE TABLE " + TABLE_NAME + "( " + PERSON_TABLE_COLUMN_ID + " INTEGER PRIMARY KEY, " +
PERSON_TABLE_COLUMN_NAME + " TEXT, " + PERSON_TABLE_COLUMN_PIN + " TEXT )";
Log.d(TAG, "onCreate SQL: " + buildSQL);
sqLiteDatabase.execSQL(buildSQL);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
// Database schema upgrade code goes here
String buildSQL = "DROP TABLE IF EXISTS " + TABLE_NAME;
Log.d(TAG, "onUpgrade SQL: " + buildSQL);
sqLiteDatabase.execSQL(buildSQL); // drop previous table
onCreate(sqLiteDatabase); // create the table from the beginning
}
}
}
对于在 2022 年遇到此问题的任何人,推荐的方法现在是Room library https://developer.android.com/training/data-storage/room
它在后台使用SQLiteOpenHelper 。
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