无法获取数据并在Android的ListView中显示

Question

MySqliteDatabase Clas:

public class MySqliteDatabase extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "EmaployeeDetail";
    private static final String TABLE_EMployee = "Employee";
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_EMAIL = "email";

    public MySqliteDatabase(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub

        String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_EMployee + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
                + KEY_EMAIL + " TEXT" + ")";
        db.execSQL(CREATE_CONTACTS_TABLE);

    }

    public void addEmployee(Employee contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.get_name()); // Contact Name
        values.put(KEY_EMAIL, contact.get_email()); // Contact Phone

        // Inserting Row
        db.insert(TABLE_EMployee, null, values);
        // 2nd argument is String containing nullColumnHack
        db.close(); // Closing database connection
    }

    public List<Employee> getAllContacts() {
        List<Employee> contactList = new ArrayList<Employee>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_EMployee;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Employee contact = new Employee();
                contact.set_id(Integer.parseInt(cursor.getString(0)));
                contact.set_name(cursor.getString(1));
                contact.set_email(cursor.getString(2));
                // Adding contact to list
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        // return contact list
        return contactList;
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_EMployee);

        // Create tables again
        onCreate(db);
    }

}

ContanctAdapter Class :

public class ContanctAdapter extends ArrayAdapter<Employee> {

    private Activity activity;
    private List<Employee> items;
    private int row;
    private Employee objBean;

    public ContanctAdapter(Activity act, int row, List<Employee> items) {
        super(act, row, items);

        this.activity = act;
        this.row = row;
        this.items = items;

    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        View view = convertView;
        ViewHolder holder;
        if (view == null) {
            LayoutInflater inflater = (LayoutInflater) activity
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            view = inflater.inflate(row, null);

            holder = new ViewHolder();
            view.setTag(holder);
        } else {
            holder = (ViewHolder) view.getTag();
        }

        if ((items == null) || ((position + 1) > items.size()))
            return view;

        objBean = items.get(position);

        holder.tvname = (TextView) view.findViewById(R.id.tvname);

        holder.tvEmail = (TextView) view.findViewById(R.id.tvemail);

        if (holder.tvname != null && null != objBean.get_name()
                && objBean.get_name().trim().length() > 0) {
            holder.tvname.setText(Html.fromHtml(objBean.get_name()));
        }

        if (holder.tvEmail != null && null != objBean.get_email()
                && objBean.get_email().trim().length() > 0) {
            holder.tvEmail.setText(Html.fromHtml(objBean.get_email()));
        }

        return view;
    }

    public class ViewHolder {
        public TextView tvname, tvEmail;
    }

}

MainActivity Class:

public class MainActivity extends Activity {
    MySqliteDatabase db = new MySqliteDatabase(this);
    EditText nametext;
    EditText emailtext;
    Button btn;
    public List<Employee> list1 = new ArrayList<Employee>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        nametext = (EditText) findViewById(R.id.editText1);
        emailtext = (EditText) findViewById(R.id.editText2);
        btn = (Button) findViewById(R.id.button1);

        btn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                String name = nametext.getText().toString();
                String email = emailtext.getText().toString();

                db.addEmployee(new Employee(name, email));

                Toast.makeText(getApplicationContext(), "SucessfullyInseter",
                        1000).show();

            }

        });

    }

    @Override
    protected void onStart() {
        // TODO Auto-generated method stub
        super.onStart();
        List<Employee> contacts = db.getAllContacts();
        Employee emp = new Employee();
        for (Employee cn : contacts) {
            String log = "Id: " + cn.get_id() + " ,Name: " + cn.get_name()
                    + " ,Phone: " + cn.get_email();
            // Writing Contacts to log
            Log.d("Name: ", log);

            String name1 = cn.get_name();
            String Email1 = cn.get_email();

            ListView list = (ListView) findViewById(R.id.listView1);
            emp.set_name(name1);
            emp.set_email(Email1);
            contacts.add(emp);

            ContanctAdapter objAdapter = new ContanctAdapter(MainActivity.this,
                    R.layout.alluser_row, list1);
            list.setAdapter(objAdapter);

        }
    }

}

I am Able to fetch data at this line Log.d("Name: ", log); but when i Print data in listview using this Line :

ContanctAdapter objAdapter = new ContanctAdapter(MainActivity.this,
                R.layout.alluser_row, list1);
        list.setAdapter(objAdapter);

Application becomes crash i dont know what is the Problem why its Application crash please help where am doing wrong i am unable to find issue.

Heer is my stack trace:

03-24 10:20:27.850: E/AndroidRuntime(10129): FATAL EXCEPTION: main
03-24 10:20:27.850: E/AndroidRuntime(10129): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.crudexample/com.example.crudexample.MainActivity}: java.util.ConcurrentModificationException
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1964)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1989)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.ActivityThread.access$600(ActivityThread.java:126)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1155)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.os.Looper.loop(Looper.java:137)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.ActivityThread.main(ActivityThread.java:4482)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at java.lang.reflect.Method.invokeNative(Native Method)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at java.lang.reflect.Method.invoke(Method.java:511)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at dalvik.system.NativeStart.main(Native Method)
03-24 10:20:27.850: E/AndroidRuntime(10129): Caused by: java.util.ConcurrentModificationException
03-24 10:20:27.850: E/AndroidRuntime(10129):    at java.util.ArrayList$ArrayListIterator.next(ArrayList.java:569)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at com.example.crudexample.MainActivity.onStart(MainActivity.java:62)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1133)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.Activity.performStart(Activity.java:4475)
03-24 10:20:27.850: E/AndroidRuntime(10129):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1937)
03-24 10:20:27.850: E/AndroidRuntime(10129):    ... 11 more

Answer 1

You cannot modify a list you are currently iterating over. At least not the way you've done it.

    for (Employee cn : contacts) {
        ...

        contacts.add(emp);

        ...
    }

I'd tell you how to fix it but frankly your code is confusing as hell. Maybe this is what you meant:

@Override
protected void onStart() {
    // TODO Auto-generated method stub
    super.onStart();
    List<Employee> contacts = db.getAllContacts();
    for (Employee cn : contacts) {
        String log = "Id: " + cn.get_id() + " ,Name: " + cn.get_name()
                + " ,Phone: " + cn.get_email();
        // Writing Contacts to log
        Log.d("Name: ", log);
    }
    ListView list = (ListView) findViewById(R.id.listView1);
    ContanctAdapter objAdapter = new ContanctAdapter(MainActivity.this,
                R.layout.alluser_row, contacts);
    list.setAdapter(objAdapter);
}

Answer 2

As already stated there is problem in code (ConcurrentModificcationException)

To fix there is no need to iterate over a loop

 List<Employee> contacts = db.getAllContacts();
 ListView list = (ListView) findViewById(R.id.listView1);
 ContanctAdapter objAdapter = new ContanctAdapter(MainActivity.this,
                R.layout.alluser_row, contacts);
 list.setAdapter(objAdapter);

You inflate a layout for each item in listview. The number of items depends on the size of the list. There is no need for a for loop in your activity code. You have a List of Employee that is passed to Custom Adapter ie ContanctAdapter and you use the same there.

Also change

MySqliteDatabase db = new MySqliteDatabase(this)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

to

MySqliteDatabase db;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
db = new MySqliteDatabase(this);

Context is available once Activity is created.