Creating a pushbutton and callback function

I could not find the right answer after a long search.

I want to create several pushbuttons in the script:

PushButton = uicontrol(gcf,'Style', 'push', 'String', 'Next', ... 'Position', [300 10 30 30], ...
'CallBack', 'PushB');

Then when I push the pushbutton I want the program to run a related function

function PushB_Callback('variables')
display('I pushed the pushbutton')
end

How do I do this?

thanks

Answer 1

[Mischa Kim]

Try

function myButtonTest()

PushButton = uicontrol(gcf,'Style', 'push', 'String', 'Next','Position', [300 10 30 30],'CallBack', @PushB);

function PushB(source,event)
display('I pushed the pushbutton')
end

end

For more information, check out the example in the documentation.

[K VdB]

Thank you for your response.

I've tried the suggested syntax but this gives an error:

"Undefined function or variable 'PushB'."

-

Greetings

[Mischa Kim]

Copy-paste the entire code and save the function as myButtonTest.m.

[K VdB]

It will still give the same error.

-

Thanks for the response

[Mischa Kim]

Just to make sure, there is only one MATLAB file, named myButtonTest.m. The PushB function is nested within myButtonTest.

[Jan]

@Mischa: And because PushB is nested, evaluating it as a string will not work. Callbacks defined as a string are evaluated in the base workspace. So better use a function handle.

[Mischa Kim]

@Simon: Absolutely. I just copy-pasted the code without replacing the quotation marks. Thanks.

[K VdB]

It works! Fantastic!

Answer 2

[Jan]

Use a function handle:

function main()
PushButton = uicontrol(gcf,'Style', 'push', 'String', 'Next', ...
            'Position', [300 10 30 30], ...
            'CallBack', @PushB_Callback);  % [EDITED, Typo: "_Callback" added]
end

function PushB_Callback(ObjectH, EventData)
display('I pushed the pushbutton')
end

[K VdB]

Then I get the following error:

Undefined function 'PushB' for input arguments of type 'matlab.ui.control.UIControl'.

_

Greetings

[Jan]

@K Vdb: This is a type. Do you see, that I've written "@PushB" but called the function "PushB_Callback"? Come on, try to follow the intention of the code.

[Brian Njenga]

What is ObjectH in the function handle

[Walter Roberson]

@Brian Njenga

In MATLAB, callback functions are automatically passed at least two parameters.

The first parameter is the handle of the object for which the callback is taking place. This allows you to use the same callback function for different objects, with the function using the passed-in handle to know which object it was invoked for. So in the case of this sample code, the first parameter, here called ObjectH, will be passed as the handle of the uicontrol -- it will have the same value as PushButton has.

The second parameter is event information that describes in more detail what was requested. For most kinds of callbacks, there is no additional information and [] is passed. For some kinds of callbacks such as WindowsButtonPressFcn the parameter is a struct that has information about which button (or key) was pressed, or what the current bounds are (for constraint callbacks), and so on.

For uicontrol associated with "traditional" figures, when using Callback, then the event data will be a object of type ActionData, that has a property Source (which will be a handle to the control that was activated), and property EventName, which will be the character vector with content 'Action'