我使用 SQLiteManager 创建了一个包含一个表的数据库文件 (.db)，TEstTable并将其粘贴到/assets文件夹中。我想从我的 Android 应用程序对此数据库执行操作。
为此，我按照Stack Overflow 上的建议遵循了本教程。
添加了更多代码来读取它并将结果保存在字符串中并打印该结果，准确地说我只添加了一个原始查询。
检查我的 DatabaseHelper 类代码：
public class DatabaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static final String DB_PATH = "/data/data/com.example.sqlitemanagerexample/databases/";
private static final String DB_NAME = "managerSample";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor Takes and keeps a reference of the passed context in order to
* access to the application assets and resources.
*
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own
* database.
* */
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
// do nothing - database already exist
} else {
// By calling this method and empty database will be created into
// the default system path
// of your application so we are gonna be able to overwrite that
// database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each
* time you open the application.
*
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
/* database does't exist yet. */
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created
* empty database in the system folder, from where it can be accessed and
* handled. This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException {
// Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
// Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
// transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
// Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException {
// Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if (myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public String getEntries() {
Cursor c = myDataBase.rawQuery("SELECT * FROM TestTable ;", null);
String result = "";
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
result = result + c.getShort(0) + c.getString(1) + c.getString(2);
}
return result;
}
// Add your public helper methods to access and get content from the
// database.
// You could return cursors by doing "return myDataBase.query(....)" so it'd
// be easy
// to you to create adapters for your views.
}
查看活动的代码：
public class View extends Activity {
TextView tv;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.viewdb);
tv = (TextView) findViewById(R.id.textView1);
DatabaseHelper myDbHelper ;
myDbHelper = new DatabaseHelper(this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
} catch (SQLException sqle) {
throw sqle;
}
tv.setText(myDbHelper.getEntries());
}
}
当我运行此代码时，视图活动未启动并且应用程序被强制关闭。Logcat 说：
E / AndroidRuntime（1764）：java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.sqlitemanagerexample/com.example.sqlitemanagerexample.View}：android.database.sqlite.SQLiteException：没有这样的表：TestTable：，而编译： SELECT * FROM TestTable ；
android.database.sqlite.SQLiteException：没有这样的表：TestTable：，编译时：SELECT * FROM TestTable；