Creating Graphical User Interfaces

Loading the List Box

This example creates a subfunction to load items into the list box. This subfunction accepts the path to a directory and the handles structure as input arguments. It performs these steps:

• Change to the specified directory so the GUI can navigate up and down the tree as required.
• Use the dir command to get a list of files in the specified directory and to determine which name is a directory and which is a file. dir returns a structure (dir_struct) with two fields, name and isdir, which contain this information.
• Sort the file and directory names (sortrows) and save the sorted names and other information in the handles structure so this information can be passed to other functions.

• The name structure field is passed to sortrows as a cell array, which is transposed to get one file name per row. The isdir field and the sorted index values, sorted_index, are saved as vectors in the handles structure.

• Call guidata to save the handles structure.
• Set the list box String property to display the file and directory names and set the Value property to 1. This is necessary to ensure Value never exceeds the number of items in String, since MATLAB updates the Value property only when a selection occurs and not when the contents of String changes.
• Displays the current directory in the text box by setting its String property to the output of the pwd command.

The load_listbox function is called by the opening function of the GUI M-file as well as by the list box callback.

• function load_listbox(dir_path, handles)
  cd (dir_path)
  dir_struct = dir(dir_path);
  [sorted_names,sorted_index] = sortrows({dir_struct.name}');
  handles.file_names = sorted_names;
  handles.is_dir = [dir_struct.isdir];
  handles.sorted_index = [sorted_index];
  guidata(handles.figure1,handles)
  set(handles.listbox1,'String',handles.file_names,...
      'Value',1)
  set(handles.text1,'String',pwd)
  

The List Box Callback

The list box callback handles only one case: a double-click on an item. Double clicking is the standard way to open a file from a list box. If the selected item is a file, it is passed to the open command; if it is a directory, the GUI changes to that directory and lists its contents.

Defining How to Open File Types

The callback makes use of the fact that the open command can handle a number of different file types. However, the callback treats FIG-files differently. Instead of opening the FIG-file, it passes it to the guide command for editing.

Determining Which Item the User Selected

Since a single click on an item also invokes the list box callback, it is necessary to query the figure SelectionType property to determine when the user has performed a double click. A double-click on an item sets the SelectionType property to open.

All the items in the list box are referenced by an index from 1 to n, where 1 refers to the first item and n is the index of the nth item. MATLAB saves this index in the list box Value property.

The callback uses this index to get the name of the selected item from the list of items contained in the String property.

Determining if the Selected Item is a File or Directory

The load_listbox function uses the dir command to obtain a list of values that indicate whether an item is a file or directory. These values (1 for directory, 0 for file) are saved in the handles structure. The list box callback queries these values to determine if current selection is a file or directory and takes the following action:

• If the selection is a directory -- change to the directory (cd) and call load_listbox again to populate the list box with the contents of the new directory.
• If the selection is a file -- get the file extension (fileparts) to determine if it is a FIG-file, which is opened with guide. All other file types are passed to open.

The open statement is called within a try/catch block to capture errors in an error dialog (errordlg), instead of returning to the command line.

• function listbox1_Callback(hObject, eventdata, handles)
  if strcmp(get(handles.figure1,'SelectionType'),'open') % If double click
      index_selected = get(handles.listbox1,'Value');
      file_list = get(handles.listbox1,'String');
      filename = file_list{index_selected}; % Item selected in list box
      if  handles.is_dir(handles.sorted_index(index_selected)) % If directory
          cd (filename)
          load_listbox(pwd,handles) % Load list box with new directory
      else
          [path,name,ext,ver] = fileparts(filename);
          switch ext
          case '.fig' 
              guide (filename) % Open FIG-file with guide command
          otherwise 
              try
                   open(filename) % Use open for other file types
              catch
                   errordlg(lasterr,'File Type Error','modal')
              end
          end
      end
  end
  

Opening Unknown File Types

You can extend the file types that the open command recognizes to include any file having a three-character extension. You do this by creating an M-file with the name openxyz, where xyz is the extension. Note that the list box callback does not take this approach for FIG-files since openfig.m is required by the GUI M-file. See open for more information.

Specifying the Directory to List

Accessing Workspace Variables from a List Box

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