MATLAB: How to set simulink model parameter from GUI during simulation

guiMATLABsimulationsimulink

I want to set the gain(value of K) in the simulink block when this model is simulating.
I created a GUI contains a button and an edit text(tagged "text_box"), and the callback function of this button will set the gain by specifying the K in base work space.
    % --- Executes on button press in FK_button.

    function FK_button_Callback(hObject, eventdata, handles)
    % hObject    handle to FK_button (see GCBO)

    % eventdata  reserved - to be defined in a future version of MATLAB

    % handles    structure with handles and user data (see GUIDATA)

    global K;
    text=get(handles.text_box, 'String');
    value = str2double(text);
    K = value;
However, the simulink block only read the value of K in work space when I started simulation. During the simulation, if I press the button, the K value in base work space would change to the value I set, but the value of K in simulink wouldn't change.
I've also tried using set_param API to change the K in simulink by
    % --- Executes on button press in FK_button.
    function FK_button_Callback(hObject, eventdata, handles)
    % hObject    handle to FK_button (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)
    global K;
    text=get(handles.text_box, 'String');
    value = str2double(text);
    %gui_variable is the model file name
    set_param('gui_variable/Gain','Gain', value);
But I'll got error saying:
    Error using robotics_gui_2>FK_button_Callback (line 429)
    Invalid setting in Gain block 'Gain' for parameter 'Gain'
What can I do to alter K in simulink during simulation?

Best Answer

   set_param('gui_variable/Gain','Gain', value);
Is value string?
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