列表视图中的项目不会出现

Question

我尝试在列表视图中显示项目，添加新联系人然后将其添加到列表视图时，添加新联系人时不会显示。 这是main_fragment

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_main, container, false);
    ImageView contactImage;
    final EditText nametxt, emailTxt, phoneTxt, addressTxt;
    nametxt = (EditText) view.findViewById(R.id.txtName);
    emailTxt = (EditText) view.findViewById(R.id.txtEmail);
    phoneTxt = (EditText) view.findViewById(R.id.txtPhone);
    addressTxt = (EditText) view.findViewById(R.id.txtAddress);
    dbHandler = new DatabaseHandler(getActivity().getApplicationContext());



    final Button addBtn = (Button) view.findViewById(R.id.btnadd);
    addBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Uri imageUri = Uri.parse("android.resource://org.intracode.contactmanager/drawable/no_user_logo.png");
            import_fragment.Contact contact = new import_fragment.Contact(dbHandler.getContactsCount(), String.valueOf(nametxt.getText()), String.valueOf(phoneTxt.getText()), String.valueOf(emailTxt.getText()), String.valueOf(addressTxt.getText()), imageUri);
            if (!contactExists(contact)) {
                dbHandler.createContact(contact);
                Contacts.add(contact);
                if (contactAdapter != null) contactAdapter.notifyDataSetChanged();
                Toast.makeText(getActivity().getApplicationContext(), String.valueOf(nametxt.getText()) + " has been added to your Contacts!", Toast.LENGTH_SHORT).show();
                resetAddContactPanel();
                return;
            }
            Toast.makeText(getActivity().getApplicationContext(), String.valueOf(nametxt.getText()) + " already exists. Please use a different name.", Toast.LENGTH_SHORT).show();
        }
    });



    final Button addContact = (Button) view.findViewById(R.id.btnadd);

    nametxt.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {

            addContact.setEnabled(!nametxt.getText().toString().trim().equals(""));


        }

        @Override
        public void afterTextChanged(Editable s) {

        }
    });


    return view;


}

ArrayAdapter<import_fragment.Contact> contactAdapter;
ListView contactListView;
DatabaseHandler dbHandler;
int longClickedItemIndex;



public void onActivityResult(int reqCode, int resCode, Intent data) {
    Uri imageUri = Uri.parse("android.resource://org.intracode.contactmanager/drawable/no_user_logo.png");
    ImageView contactImageImgView;
    contactImageImgView = (ImageView) getActivity().findViewById(R.id.ivContactImage);

    if (resCode == Activity.RESULT_OK) {
        if (reqCode == 1) {
            imageUri = data.getData();
            contactImageImgView.setImageURI(data.getData());
        }
    }
}


private void resetAddContactPanel() {
    final EditText nametxt, emailTxt, phoneTxt, addressTxt;
    nametxt = (EditText) getActivity().findViewById(R.id.txtName);
    emailTxt = (EditText) getActivity().findViewById(R.id.txtEmail);
    phoneTxt = (EditText) getActivity().findViewById(R.id.txtPhone);
    addressTxt = (EditText) getActivity().findViewById(R.id.txtAddress);
    nametxt.setText("");
    phoneTxt.setText("");
    emailTxt.setText("");
    addressTxt.setText("");
}

public void onCreateContextMenu(ContextMenu menu, View view, ContextMenu.ContextMenuInfo menuInfo) {
    super.onCreateContextMenu(menu, view, menuInfo);

    {
        ImageView contactImageImgView;

        contactImageImgView = (ImageView) view.findViewById(R.id.ivContactImage);

        contactImageImgView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setType("image/*");
                intent.setAction(Intent.ACTION_GET_CONTENT);
                startActivityForResult(Intent.createChooser(intent, "Select Contact Image"), 1);
            }

        });


        if (dbHandler.getContactsCount() != 0)
            Contacts.addAll(dbHandler.getAllContacts());

        populateList();
    }


    menu.setHeaderIcon(R.drawable.pencil_icon);
    menu.setHeaderTitle("Contact Options");
    menu.add(Menu.NONE, EDIT, menu.NONE, "Edit Contact");
    menu.add(Menu.NONE, DELETE, menu.NONE, "Delete Contact");
}


public boolean onContextItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case EDIT:
            // TODO: Implement editing a contact
            break;
        case DELETE:
            dbHandler.deleteContact(Contacts.get(longClickedItemIndex));
            Contacts.remove(longClickedItemIndex);
            contactAdapter.notifyDataSetChanged();
            break;
    }

    return super.onContextItemSelected(item);
}



private boolean contactExists(import_fragment.Contact contact) {

    String name = contact.getName();
    int contactCount = Contacts.size();

    for (int i = 0; i < contactCount; i++) {
        if (name.compareToIgnoreCase(Contacts.get(i).getName()) == 0)
            return true;
    }
    return false;
}


private void populateList() {
    contactAdapter = new ContactListAdapter(getActivity());
    contactListView.setAdapter(contactAdapter);
}


final List<import_fragment.Contact> Contacts = new ArrayList<import_fragment.Contact>();

private class ContactListAdapter extends ArrayAdapter<import_fragment.Contact> {
    public ContactListAdapter(Context cntx) {
        super(cntx, R.layout.fragment_import, Contacts);
    }

    @Override
    public View getView(int position, View view, ViewGroup parent) {
        if (view == null)
            view = getActivity().getLayoutInflater().inflate(R.layout.fragment_import, parent, false);

        import_fragment.Contact currentContact = Contacts.get(position);

        TextView name = (TextView) view.findViewById(R.id.contactName);
        name.setText(currentContact.getName());
        TextView phone = (TextView) view.findViewById(R.id.phoneNumber);
        phone.setText(currentContact.getPhone());
        TextView email = (TextView) view.findViewById(R.id.emailAddress);
        email.setText(currentContact.getEmail());
        TextView address = (TextView) view.findViewById(R.id.cAddress);
        address.setText(currentContact.getAddress());


        return view;
    }
}

有人告诉我你必须在onCreateView中设置adapter，当我这样做时我得到错误Null所以我删除了它，如果这将解决问题那么请告诉我如何在onCreateView中设置adapter而不会出现空错误。