MATLAB Creating Graphical User Interfaces

9 Examples of GUIDE UIs

Validate Input as Numbers

When you UI displays, you can type parameters into three edit text fields as strings

of text. If you type an invalid value, the graphs can fail to inform or even to generate.

Preventing bad inputs from being processed is an important function of almost any UI

that performs computations. This UI code validates these inputs:

• Ensure all three inputs are positive or negative real numbers


• Ensures that the t (time) input is a vector that increases monotonically and is not too
  long to display

Validate all three inputs are positive or negative real numbers

In this example, each edit text control callback validates its input. If the input fails

validation, the callback disables the Plot button, changes its String to indicate the

type of problem encountered, and restores focus to the edit text control, highlighting

the erroneous input. When you enter a valid value, the Plot button reenables with its

String set back to 'Plot'. This approach prevents plotting errors and avoids the need

for an error dialog box.

The str2double function validates most cases, returning NaN (Not a Number) for

nonnumeric or nonscalar string expressions. An additional test using the isreal

function makes sure that a text edit field does not contain a complex number, such as

'4+2i'. The f1_input_Callback contains the following code to validate input for f1 :

function f1_input_Callback(hObject, eventdata, handles)

% Validate that the text in the f1 field converts to a real number

f1 = str2double(get(hObject,'String'));

if isnan(f1) || ~isreal(f1)

% isdouble returns NaN for non-numbers and f1 cannot be complex

% Disable the Plot button and change its string to say why

set(handles.plot_button,'String','Cannot plot f1')

set(handles.plot_button,'Enable','off')

% Give the edit text box focus so user can correct the error

uicontrol(hObject)

else

% Enable the Plot button with its original name

set(handles.plot_button,'String','Plot')

set(handles.plot_button,'Enable','on')

end

Similarly, f2_input_Callback code validates the f2 input.

Validate the Time Input Vector

The time vector input, t, is more complicated to validate. As the str2double function

does not operate on vectors, the eval function is called to convert the input string into