未创建 Sqlite 数据库

Question

我正在尝试创建一个使用一次登录的应用程序。当它打开时，它会检查 sqlite db 是否存在。如果存在，它会转到本地登录页面。 如果数据库不存在，它会创建一个新的数据库。 我一直在检查数据库部分。我尝试使用this 和this。它没有用。

Mainactivity.java

public class MainActivity extends Activity {

boolean exists;
SQLiteDBHelper db;
private static final String DATABASE_PATH = "/data/data/com.example.pos_1/databases";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.start);
    db=new SQLiteDBHelper(this);
    exists=db.checkDataBase();
    if(exists)
    {
        Toast.makeText(getApplicationContext(),"db present",Toast.LENGTH_LONG).show();
        MainActivity.this.startActivity(new Intent(MainActivity.this, Activity_three.class));
    }
    else
    {

        Toast.makeText(getApplicationContext(),"db absent",Toast.LENGTH_LONG).show();
        MainActivity.this.startActivity(new Intent(MainActivity.this, ActivityTwo.class));
    }
}

SQLiteDBHelper

public class SQLiteDBHelper extends SQLiteOpenHelper{
private static final String DATABASE_NAME = "local";
private static final int DATABASE_VERSION = 1;

private static final String DATABASE_PATH = "/data/data/com.example.pos_1/databases/";
public static final String TABLE_NAME = "users";

Context context;




//modified constructor
public SQLiteDBHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    this.context = context;

}

/*public class MyClass {

    private Context cont;

   // public MyClass(Context c) {
        //cont = c;
    //}

    public boolean MyClass(Context context) {
        File dbFile = new File(DATABASE_PATH + DATABASE_NAME);
        Toast.makeText(context, "db exists", Toast.LENGTH_LONG).show();
        return dbFile.exists();
    }
}*/

public boolean checkDataBase() {
    /*SQLiteDatabase checkDB = null;
        checkDB = SQLiteDatabase.openDatabase(DATABASE_PATH, null,
                SQLiteDatabase.OPEN_READONLY);
        checkDB.close();

        if(checkDB==null)
        {
            Toast.makeText(this.context,"error",Toast.LENGTH_LONG).show();
            return false;
        }
        else
            return true;
    SQLiteDatabase checkDB = null;

    try{
        String myPath = DATABASE_PATH + DATABASE_NAME;
        checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
    }catch(SQLiteException e){

        Toast.makeText(this.context,"error",Toast.LENGTH_LONG).show();
        //database does't exist yet.
    }

    if(checkDB != null){
        Toast.makeText(this.context,"check",Toast.LENGTH_LONG).show();
        checkDB.close();
    }

    return checkDB != null ? true : false;

    Log.v(TAG, "is DB present Entry!!!");
    boolean checkFlag = true;
    SQLiteDatabase testDb;
    String testPath = DATABASE_PATH + DATABASE_NAME;
    try {
        Log.v(TAG, "try block1");
        this.getDatabaseName();
        testDb = SQLiteDatabase.openDatabase(testPath, null,
                SQLiteDatabase.OPEN_READWRITE);
        Log.v(TAG, "try block2");
        if(testDb!=null)
            return  true;
    }
    catch(SQLiteException sqlException){
        Toast.makeText(context,sqlException.getMessage(),Toast.LENGTH_LONG);
        Log.v(TAG, "DB absent");
        checkFlag=false;
    }
    //Log.v(TAG, "is DB present Exit!!!");
    return checkFlag;*/
    try{
        Log.d("opendb","before opening");
        SQLiteDatabase   dbe = SQLiteDatabase.openDatabase("/data/data/com.example.pos_1/databases/local", null,0);
        Log.d("opendb","EXIST");
        dbe.close();
        return true;
    }

    catch (SQLiteException sqlException)
    {
        Log.d("opendb","NOT EXIST");
        return  false;
    }
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {

    //sqLiteDatabase.execSQL("create table rhbus(USERNAME TEXT PRIMARY KEY,PASSWORD TEXT)");
    executeSQLScript(sqLiteDatabase, "create.sql");

}
private void executeSQLScript(SQLiteDatabase database,String dbname) {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    byte buf[] = new byte[1024];
    int len;
    AssetManager assetManager = context.getAssets();

    InputStream inputStream = null;

    try{
        inputStream = assetManager.open(dbname);
        while ((len = inputStream.read(buf)) != -1) {
            outputStream.write(buf, 0, len);
        }
        outputStream.close();
        inputStream.close();

        String[] createScript = outputStream.toString().split(";");
        for (int i = 0; i < createScript.length; i++) {
            String sqlStatement = createScript[i].trim();

            if (sqlStatement.length() > 0) {
                database.execSQL(sqlStatement + ";");
            }
        }
    } catch (IOException e){

    } catch (SQLException e) {

    }
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
    onCreate(sqLiteDatabase);
}

Answer 1

我相信您的问题是因为从来没有尝试打开数据库，因此永远不会调用 onCreate 方法。

我建议在 SQLiteDBHelper 的构造函数中添加强制打开数据库的尝试。例如通过使用：-

public SQLiteDBHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    this.context = context;
    this.getWritableDatabase(); //<<<< force invocation of the onCreate method if the database doesn't exist.
}

executeSQLScript 的以下替换也可能会有所帮助（添加了提取的 SQL 语句的日志记录）

private void executeSQLScript(SQLiteDatabase database, String dbname) {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    byte buf[] = new byte[1024];
    int len;
    AssetManager assetManager = context.getAssets();

    InputStream inputStream = null;

    try {
        inputStream = assetManager.open(dbname);
        while ((len = inputStream.read(buf)) != -1) {
            outputStream.write(buf, 0, len);
        }
        outputStream.close();
        inputStream.close();

        String[] createScript = outputStream.toString().split(";");
        for (int i = 0; i < createScript.length; i++) {
            Log.d("DBCreate","Read Line :- " + createScript[i].toString());
            String sqlStatement = createScript[i].trim();


            if (sqlStatement.length() > 0) {
                database.execSQL(sqlStatement + ";");
            }
        }
    } catch (IOException e) {

    } catch (SQLException e) {

    }
}

注意！

如果遇到故障，上述更改将导致创建数据库，因此修复和重新运行需要删除数据库（删除应用程序数据或卸载应用程序）