Matlab Training Session 13: Creating Gui

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Matlab Training Session 13Creating Guis
Course Website http//www.queensu.ca/neurosci/Mat
lab Training Sessions.htm
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• Course Outline
• Term 1
• Introduction to Matlab and its Interface
• Fundamentals (Operators)
• Fundamentals (Flow)
• Importing Data
• Functions and M-Files
• Plotting (2D and 3D)
• Term 2
• Term 1 review
• Plotting (2D and 3D)
• Statistical Tools in Matlab
• Nonlinear Curve Fitting
• Statistical Tools in Matlab II
• GUIs

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GUI

• Graphical User Interface
• A tool for interacting with the computer

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How is this useful?

• Visually interaction with data is often simpler
  and more intuitive
• Faster manipulation of data
• Interactive
• Easy to Learn!
• Fool Proof

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Some Examples

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Components of a GUI

• Front End
• point of interaction with user
• Back End
• where the action is, the code controlling the
  graphics and the different widgets

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Components of a GUI

• Front End
• Select and place different objects (widgets) on
  the graphical layout. These will the what the
  user interacts with.
• Underlying the GUI is the backend which controls
  how the GUI reacts on an event.
• This is called event-driven programming

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Components of a GUI

• Back End
• The code underlying the frontend graphics.
• Matlab gives a basis and you fill in the details

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In Matlab

• Matlab provides interactive tool for creating the
  graphics and underlying code for GUIs
• Function is called GUIDE
• Provides some templates for simple GUIs that can
  be expanded as need be
• Launch GUIDE in Matlab and select on of the
  pre-made templates (ie. not Blank)

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GUI with Axis and Menu

• This is the layout for a simple GUI that allows
  you to select one of 5 pre-made plots.
• Not very useful but a good basis to start with
• Press the Launch button and save
• You will see the screen and you can interact with
  it

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Backend of Axis and Menu

• When you launch the GUI created the .fig file
  which is the graphics and the .m file which is
  the underlying code that control the widget.
• Take a Look at the .m file
• It looks like a mess, but it is not so bad!
• Lets explore this code
• First lets understand the basic m-file format
  template for an empty GUI

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Functions and Callbacks in the M-File

• Common Input Arguments
• All functions in the M-file have the following
  input arguments corresponding to the handles
  structure
• hObject -- the handle to the figure or Callback
  object
• handles -- structure with handles and user data
  
• The handles structure is saved at the end of each
  function with the command
• guidata(hObject, handles)

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Functions and Callbacks in the M-File

• Sharing Data with the Handles Structure
• When you run a GUI, the M-file creates a
  handles structure that contains all the data for
  GUI objects, such as controls, menus, and axes.
• The handles structure is passed as an input to
  each callback (user interface).
• You can use the handles structure to Share data
  between callbacks using the guidata function

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Functions and Callbacks in the M-File
Sharing Data To store data that is contained in
a variable X, set a field of the handles
structure equal to X and then save the handles
structure with the guidata function
handles.current_data X guidata(hObject,handle
s) You can retrieve the data in any other
callback with the command X
handles.current_data
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Functions and Callbacks in the M-File

• You can add code to the following parts of the
  GUI M-file
• Opening function -- executes before the GUI
  becomes visible to the user.
• Output function -- outputs data to the command
  line, if necessary.
• Callbacks -- execute each time the user
  activates the corresponding component of the GUI.
  

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Functions and Callbacks in the M-File

• Opening Function
• The opening function contains code that is
  executed just before the GUI is made visible to
  the user.
• You can access all the components for the GUI
  in the opening function, because all objects in
  the GUI are created before the opening function
  is called.
• You can add code to the opening function to
  perform tasks that need to be done before the
  user has access to the GUI
• This includes
• creating data, plots or images, or making the GUI
  blocking with the uiwait command.

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• uiwait
• The command uiwait makes the M-file halt
  execution
• This is useful to force the program to pause
  execution until a user activates a some component
  in the GUI.
• The uiresume command allows the M-file to
  resume execution once the user input is complete

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Functions and Callbacks in the M-File

• Opening Function
• For a GUI whose file name is my_gui, the
  definition line for the opening function is
• function my_gui_OpeningFcn(hObject, eventdata,
  handles, varargin)
• Besides the arguments hObject and handles, the
  opening function has the following input
  arguments
• eventdata -- reserved for a future version of
  MATLAB
• varargin -- command line arguments to untitled

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Functions and Callbacks in the M-File

• Opening Function (varargin)
• All command line arguments are passed to the
  opening function via varargin.
• If you open the GUI with a property
  name/property value pair as arguments, the GUI
  opens with the property set to the specified
  value.
• For example
• my_gui('Position', 71.8 44.9 74.8 19.7)
• opens the GUI at the specified position, since
  Position is a valid figure property

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Functions and Callbacks in the M-File
Output Function The output function returns
output arguments to the command line. GUIDE
generates the following output function ---
Outputs from this function are returned to the
command line. function varargout
my_gui_OutputFcn(hObject, eventdata, handles)
Get default command line output from handles
structure varargout1 handles.output
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Functions and Callbacks in the M-File

• Callbacks
• When a user activates a component of the GUI,
  the GUI executes the corresponding callback.
• The name of the callback is determined by the
  component's Tag property and the type of
  callback.
• For example, a push button with the Tag
  print_button executes the callback
• function print_button_Callback(hObject,
  eventdata, handles)

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Functions and Callbacks in the M-File

• Output Function
• By default the output is the handle to the GUI,
  which is assigned to handles.output in the
  opening function.
• To make the GUI return a different output (eg.
  return the result of a user response, such as
  pressing a push button)
• Add the command uiwait to the opening function
• For each component of the GUI where you expect
  a user response, make the callback update the
  value of handles.output, and execute uiresume.
• handles.output some response string'
• guidata(hObject, handles)
• uiresume

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Property Inspector

• Adjusts the details of the different widgets

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Something Useful?

• Now, lets try and build something that we may
  actually use. How about a simple program that
  combines loading, plotting and calculating some
  simple statistics on preformatted data
• Create a GUI that will load week8_testdata2.txt,
  plot the data points as well as a linear
  regression
• Hint, All you need are simple push buttons and an
  axis for plotting

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Programming GUI controls

• Push Buttons
• Work like independent functions
• Each button function is passed all data from
  the GUI handles
• --- Executes on button press in Exit.
• function Exit_Callback(hObject, eventdata,
  handles)
• hObject handle to Exit (see GCBO)
• eventdata reserved - to be defined in a future
  version of MATLAB
• handles structure with handles and user data
  (see GUIDATA)
• close gcf
• Detailed descriptions of all GUI callback
  controls can be found within the GUIDE help menu.

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Layout the GUI