Creating Graphical User Interfaces

Paging Through the Address Book - Prev/Next

The Prev and Next buttons page back and forth through the entries in the address book. Both push buttons use the same callback, Prev_Next_Callback. You must set the Callback property of both push buttons to call this subfunction, as the following illustration of the Prev push button Callback property setting shows.

Determining Which Button Is Clicked

The callback defines an additional argument, str, that indicates which button, Prev or Next, was clicked. For the Prev button Callback property (illustrated above), the Callback string includes 'Prev' as the last argument. The Next button Callback string includes 'Next' as the last argument. The value of str is used in case statements to implement each button's functionality (see the code listing below).

Paging Forward or Backward

Prev_Next_Callback gets the current index pointer and the addresses from the handles structure and, depending on which button the user presses, the index pointer is decremented or incremented and the corresponding address and phone number are displayed. The final step stores the new value for the index pointer in the handles structure and saves the updated structure using guidata.

Code Listing

• function Prev_Next_Callback(hObject, eventdata,handles,str)
  % Get the index pointer and the addresses
  index = handles.Index;
  Addresses = handles.Addresses;
  % Depending on whether Prev or Next was clicked change the display
  switch str
  case 'Prev'
      % Decrease the index by one
      i = index - 1;
      % If the index is less then one then set it equal to the index of the 
      % last element in the Addresses array
      if i < 1
          i = length(Addresses);
      end
  case 'Next'
      % Increase the index by one
      i = index + 1;
      % If the index is greater than the size of the array then point
      % to the first item in the Addresses array
      if i > length(Addresses)
          i = 1;
      end 
  end
  % Get the appropriate data for the index in selected
  Current_Name = Addresses(i).Name;
  Current_Phone = Addresses(i).Phone;
  set(handles.Contact_Name,'string',Current_Name)
  set(handles.Contact_Phone,'string',Current_Phone)
  % Update the index pointer to reflect the new index
  handles.Index = i;
  guidata(hObject, handles)
  

The Contact Phone Number Callback

Saving Changes to the Address Book from the Menu