I am try to read exisiting sqlite database from assets folder! But I am getting this error:
java.lang.runtimeexception unable to instantiate activity componentinfo
Please help me out!
This is my DataBaseHelper Class:
public class DataBaseHelper extends SQLiteOpenHelper {
// The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.example.sqltest/databases/";
private static String DB_NAME = "test.sqlite";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**`enter code here`
* 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();
this.close();
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) {
}
// 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.
}
This is MainActivity class:
public class MainActivity extends Activity {
DataBaseHelper myDbHelper;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public MainActivity(Context context) {
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;
}
}
}
Can anyone provide the simplest code to display the data of my existing sqlite database?
I can't think of any good reason to do anything in the constructor for this Activity subclasses(in your case).Usually you never construct an activity directly,we often use Intent,and I guess that is problem of your code.Use onCreate() instead of it's constructor,and do all of your normal static set up — create views, bind data to lists,database and so on in onCreate().
Edit1:
You can easily solve java.lang.runtimeexception unable to instantiate activity componentinfo,only change MainActivity :
public class MainActivity extends Activity {
DataBaseHelper myDbHelper;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
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;
}
}
}
Edit2:
Be sure that you place test.sqlite in assets folder of your project and the name of package of your project is com.example.sqltest.
If your code has no other problems,it will work.It means that your database is copied successfully and it is ready to use.Now you have to access and get content from database.Pay attention to comments at the end of class :
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.
If you see black page,it may because your layout is empty.You can use your database to create adapters for your views,so your activity will not be empty.
You can see these pages for more details in about SQLiteOpenHelper class:
Android SQLite Database and ContentProvider - Tutorial
Android SQLite Database Tutorial