无法获取数据并在android中的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类：

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类：

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);

        }
    }

}

我能够在此行获取数据Log.d（＆＃34;名称：＆＃34;，日志）;  但是当我使用此行在listview中打印数据时：

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

应用程序崩溃我不知道为什么它的应用程序崩溃的问题请帮助我在哪里做错了我无法找到问题。

Heer是我的堆栈跟踪：

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

您无法修改当前正在迭代的列表。至少不是你做过的方式。

    for (Employee cn : contacts) {
        ...

        contacts.add(emp);

        ...
    }

我告诉你如何修复它，但坦率地说，你的代码令人困惑。也许这就是你的意思：

@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

如前所述，代码中存在问题（ConcurrentModificcationException）

要修复，不需要迭代循环

 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);

您为listview中的每个项目夸大了布局。项目数取决于列表的大小。您的活动代码中不需要for循环。您有一个List Employee传递到自定义适配器，即ContanctAdapter，您在那里使用相同的。{/ p>

同时更改

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

到

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

一旦创建了Activity，就可以使用上下文。