以下是示例代码:
public class MyDatabaseHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "test.db";
private static final int DATABASE_VERSION = 1;
// table: test
private static final String CREATE_TABLE_TEST =
"CREATE TABLE test(" +
"_id INTEGER PRIMARY KEY AUTOINCREMENT," +
"number FLOAT," +
"pow FLOAT" +
");";
public MyDatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_TABLE_TEST);
ContentValues values = new ContentValues();
double n = 5;
values.put("number", n);
values.put("pow", Math.pow(n, 2));
db.insert("test", null, values);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS test");
onCreate(db);
}
public float getPow() {
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT pow FROM test", null);
cursor.moveToFirst();
float pow = cursor.getFloat(0);
cursor.close();
return pow;
}
}
然后,将以下代码添加到活动中:
MyDatabaseHelper db = new MyDatabaseHelper(this);
float pow = db.getPow();
Log.d(TAG, "pow: " + pow);
在日志中,将打印计算结果,即25.0。