無法從Android中的數據庫填充listView中的數據

Question

我正在開發一個Android應用程序，我想在其中存儲我的員工詳細信息。 我無法從數據庫加載ListView中的數據。

DatabaseHelper.java

\\import statement 
 public class DatabaseHelper extends SQLiteOpenHelper{

    public static final String EMPLOYEE_ID = "EmployeeId";
    public static final String EMPLOYEE_NAME = "Name";
    public static final String EMPLOYEE_USERNAME = "Username";
    public static final String EMPLOYEE_PASSWORD = "Password";
    public static final String EMPLOYEE_MANGER_ID = "ManagerId";

    public static final String CREATE_TABLE_EMPLOYEE = "CREATE TABLE "+TABLE_NAME_EMPLOYEE+" ("+EMPLOYEE_ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+EMPLOYEE_NAME+" varchar(30), "+EMPLOYEE_USERNAME+" varchar(8), "+EMPLOYEE_PASSWORD+" varchar(10), "+EMPLOYEE_MANGER_ID+" Int);";

    public static final String DROP_TABLE_EMPLOYEE = "DROP TABLE "+TABLE_NAME_EMPLOYEE+" IF EXISTS";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        this.context = context;         
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        try {
            db.execSQL(CREATE_TABLE_EMPLOYEE);
        } catch (SQLException e) {
            //toast message
        }
        //toast message
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        try {
            db.execSQL(DROP_TABLE_EMPLOYEE);
            onCreate(db);
        } catch (SQLException e) {
            //toast message 
        }
        //toast message
    }   
}

我還有另一個只處理employeetable的類，例如插入，刪除等，即從DatabaseHelper派生的EmployeeDatabaseHelper。

EmployeeDatabaseHelper.java

\\import statement
public class EmployeeDatabaseHelper extends DatabaseHelper{

public EmployeeDatabaseHelper(Context context) {
    super(context); 
}

public Cursor getAllEmployee(){

    ArrayList<Employee> employeeArrayList = new ArrayList<Employee>();
    String sql = "select * from tblEmployee";
    SQLiteDatabase db = getWritableDatabase();
    Cursor cursor = db.rawQuery(sql, null);
    if (cursor.moveToFirst()) {
        do{
            Employee e  = new Employee();
            e.name = cursor.getString(cursor.getColumnIndex(EMPLOYEE_NAME));
            employeeArrayList.add(e);               
        } while (cursor.moveToNext());
    }       
    return cursor;  
}
}

EmployeeFragment在本節中我的代碼是錯誤的，它給出了空指針Exception。 當我打開Employeefragment時，我的應用程序關閉。

EmployeeFragment.java

public class EmployeeFragment extends Fragment {

EmployeeDatabaseHelper dbHelper;
ListView employeeList;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_employee, container, false);
    employeeList = (ListView) rootView.findViewById(R.id.employeeList);
    populateEmployeeList();
    return rootView;
}

public void populateEmployeeList(){

    Cursor cursor = dbHelper.getAllEmployee();
    String[] data = new String[] {dbHelper.EMPLOYEE_ID, dbHelper.EMPLOYEE_NAME};
    int[] id = new int[] {R.id.mainTextView, R.id.subTextView};
    SimpleCursorAdapter myAdapter = new SimpleCursorAdapter(getActivity(), R.layout.row, cursor, data, id);
    employeeList.setAdapter(myAdapter);

}
}

Employee.java是我的另一門課

public class Employee {
 public String username;
 public String name;
 public String password;        
}

在row.xml中，只有兩個textView沒有什么好用的 。 （即mainTextView，subTextView）和fragment_employee.xml中，我有一個按鈕可以添加新員工。 一個列表以查看所有員工。 我卡在這里。 如果我評論此populateEmployeeList（）類，則我的程序可以工作。 否則會意外關閉。

LOG貓

 FATAL EXCEPTION: main
  Process: com.threepin.deepakcorporation, PID: 9393
  java.lang.IllegalArgumentException: column '_id' does not exist
  at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:303)
  at android.widget.CursorAdapter.init(CursorAdapter.java:172)
  at android.widget.CursorAdapter.<init>(CursorAdapter.java:120)
  at android.widget.ResourceCursorAdapter.<init>(ResourceCursorAdapter.java:52)
  at android.widget.SimpleCursorAdapter.<init>(SimpleCursorAdapter.java:78)
  at com.threepin.deepakcorporation.EmployeeFragment.populateEmployeeList(EmployeeFragment.java:61)
  at com.threepin.deepakcorporation.EmployeeFragment.onActivityCreated(EmployeeFragment.java:52)
  at android.app.Fragment.performActivityCreated(Fragment.java:1708)
  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:908)
  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
  at android.app.BackStackRecord.run(BackStackRecord.java:684)
  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1447)
  at android.app.FragmentManagerImpl$1.run(FragmentManager.java:443)
  at android.os.Handler.handleCallback(Handler.java:733)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at android.os.Looper.loop(Looper.java:136)
  at android.app.ActivityThread.main(ActivityThread.java:5127)
  at java.lang.reflect.Method.invokeNative(Native Method)
  at java.lang.reflect.Method.invoke(Method.java:515)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:641)
  at dalvik.system.NativeStart.main(Native Method)

Answer 1

嘗試在片段的onActivityCreated()方法中使用populateEmployeeList() 。 因為按照您的代碼，您的視圖尚未完成，並且您正在嘗試通過調用populateEmployeeList()來填充listview 。

Answer 2

列_id不存在，請仔細閱讀錯誤。 您必須輸入_id字段：

@Override
public void onCreate(SQLiteDatabase paramSQLiteDatabase) {
    String sql="CREATE TABLE tableEQ (_ID INTEGER PRIMARY KEY," ...

}

Answer 3

如果我評論此populateEmployeeList（）類，則我的程序可以工作。 否則會意外關閉

由於dbHelper為null時調用getAllEmployee從方法EmployeeDatabaseHelper類。

要解決此問題，請在使用dbHelper對象訪問類中的方法之前，通過在類構造函數中傳遞Context來創建EmployeeDatabaseHelper類的對象：

 dbHelper=new EmployeeDatabaseHelper(getActivity());
 Cursor cursor = dbHelper.getAllEmployee();

Answer 4

我已經更改了代碼。 它的運行。 我不知道它是否會幫助別人，但仍然會。

DatabaseHelper.java中沒有更改

EmployeeDatabaseHelper.java

public class EmployeeDatabaseHelper {
DatabaseHelper dbhelper;

public EmployeeDatabaseHelper(Context applicationContext) {
    dbhelper= new DatabaseHelper(applicationContext);
}

public long insertEmployee(String name, String username, String password){
    SQLiteDatabase db = dbhelper.getWritableDatabase();
    ContentValues cv = new ContentValues();
    cv.put(EMPLOYEE_NAME,name);
    cv.put(EMPLOYEE_USERNAME,username);
    cv.put(EMPLOYEE_PASSWORD,password);
    long id = db.insert(TABLE_NAME_EMPLOYEE, null, cv);
    db.close();
    return id;      
}

public ArrayList<Employee> getAllEmployee(){

    ArrayList<Employee> employeeArrayList = new ArrayList<Employee>();
    SQLiteDatabase db = dbhelper.getWritableDatabase();
    Cursor cursor = db.query(TABLE_NAME_EMPLOYEE, null,null,null,null,null,null);

        while (cursor.moveToNext()) {
            Employee e  = new Employee();
            e.name = cursor.getString(cursor.getColumnIndex(EMPLOYEE_NAME));
            e.username = cursor.getString(cursor.getColumnIndex(EMPLOYEE_USERNAME));
            employeeArrayList.add(e);
        } 

    db.close();
    return employeeArrayList;
}
}

EmployeeFragment.java

public class EmployeeFragment extends Fragment {

EmployeeDatabaseHelper dbHelper;
ListView employeeList;
public Cursor employees;
private ArrayList<Employee> arrlst;
private myadapter myadapter;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_employee, container, false);

    employeeList = (ListView) rootView.findViewById(R.id.employeeList);
    return rootView;
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    populateEmployeeList();
}

public void populateEmployeeList(){

    dbHelper=new EmployeeDatabaseHelper(getActivity());
     arrlst = dbHelper.getAllEmployee();
    myadapter = new myadapter(getActivity());
    employeeList.setAdapter(myadapter);

}

class myadapter extends ArrayAdapter<Employee>{
Activity con;
private LayoutInflater Inflater;

public myadapter(Activity context) {
    super(context,R.layout.row);
    con=context;
     Inflater = (LayoutInflater)con.getSystemService(con.LAYOUT_INFLATER_SERVICE);
}

class ViewHolder{
    TextView tvid;
    TextView tvname;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    View vi = convertView;
     ViewHolder vh;
    if(vi==null){
        vh = new ViewHolder();
        vi= Inflater.inflate(R.layout.row, null);
        vh.tvid=(TextView)vi.findViewById(R.id.mainTextView);

        vh.tvname=(TextView)vi.findViewById(R.id.subTextView);
        vi.setTag(vh);

    }else{
        vh=(ViewHolder)vi.getTag();
    }
    Employee e =arrlst.get(position);
    vh.tvid.setText(e.name);
    vh.tvname.setText(e.username);
    return vi;
}
@Override
public int getCount() {
    // TODO Auto-generated method stub
    return arrlst.size();
}
}
}