some variables doesn't exist in handles after exiting callback function

MATLAB 2015a

Q1:

For example, in a callback function of a text box (Note that: I made the function name different from the 'varName')

function uiVarName_Callback(hObject, eventdata, handles)
handles.varName = get(hObject,'String');% get varName 
guidata(hObject,handles); % update gui handles

When the function exits, I cannot find varName in the handles(which I think is a master handle across the board).

In other callback functions, if I call handles.varName,

it says 'Reference to non-existent field'

Q2: How can I extract only the value of a textbox, for example, uiVarName. When I type uiVarName without a ;, then it returns as follow, which is not value in the ext box.

UIControl (uiVarName) with properties:
            Style: 'edit'
           String: 
  BackgroundColor: [0.9400 0.9400 0.9400]
         Callback: @(hObject,eventdata)sharp_gui('uiMinPkWidth_Callback',hObject,eventdata,guidata(hObject))
            Value: 
         Position: [0.0500 0.1163 0.1365 0.4419]
            Units: 'normalized'

Answer 1

[Walter Roberson]

Q2: You appear to be using R2014b or later, so you can use

uiVarName.Value

Note that the Value of a uicontrol('Style','text') has not been assigned any meaning; see http://www.mathworks.com/help/matlab/ref/uicontrol-properties.html#property_value

If you are looking for the text that has been put in the text box then

uiVarName.String

Q1:

• guidata(hObject,handles) would update the guidata (handles) structure associated with the figure that hObject belongs to. If you have multiple figures then that is not necessarily the same place that other handles references are getting the data from.
• when you use guidata() to update the master "handles" structure, other routines will not observe the update until they request the current copy of the data. If you are using GUIDE then the update should show up the next time they are called, but if you have one callback routine call another callback routine that updates the handles then the first routine will not know.

[Wenjie Wu]

Thanks for the reply. BTW, I am using guidata(hObject,handles), which (I believe) is the master 'handles' across the board. So far I don't have one callback function inside another. My goal is to access handles.x, which is updated through a callback function. But, somehow, handles.x doesn't exist in handles after exiting the callback function. However, when I am not putting a semicolon after

handles.x = str2double(get(hObject,'String'));
guidata(hObject,handles);

then, handles.x can be found in the handles after exiting the callback function.

[Walter Roberson]

No, guidata(hObject,handles) affects the handles associated with the figure that the callback object is in. If you have multiple figures that is not the same one as the master copy. guidata() is per figure.

[Wenjie Wu]

So far I have only one figure.

BTW, when I use 'handles.x.Value', after enter a new number (different from initial value) in the text box, it prompts 'Attempt to reference field of non-structure array.' Same problem happens when I use 'handles.y.String'.

[Walter Roberson]

handles.x would be a numeric value, not an graphics object.

I do not have R2014b or later to test your code against.

According to your display of uiVarName, the callback of the object does not invoke uiVarName_Callback: it is set to invoke uiMinPkWidth_Callback

[Wenjie Wu]

I am using handles.x (assuming it is a edit text box) as a example. 'handles.x.Value', gives 'Attempt to reference field of non-structure array.' Oops, in terms of 'uiMinPkWidth_Callback', I copied the wrong one.

[Adam]

You can tell very quickly whether the function is even being called or not by either putting a disp( 'Something or other' ) statement in it and seeing if that appears in your command window or just putting a breakpoint in.

That seems like the key question. Your syntax with respect to handles looks fine, but if the function never gets called then that would be the simplest explanation why the field does not exist.

[Walter Roberson]

But your handles.x is not an edit text box. Your edit text box is handles.uiVarName