Reference to non-existent field error occurring

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Aaron Smith 2017-5-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/342351-reference-to-non-existent-field-error-occurring

评论： Jan 2017-6-2

Matlab is generating the 'reference to non-existent field' error for my code. It is refering to one of my handles. Online it appears that this occurs if the field does not exist in the structure at the time the callback is set. This is not true for the offending field in my code as it is declared in the opening function and I have used guidata to update the handles structure. Is there another reason why this error should be occurring?

Error while evaluating uicontrol Callback
Reference to non-existent field 'verticalBin'.
Error in new_window_2>pushbutton4_Callback (line 190)
set(handles.verticalBin, 'enable', 'on');
Error in gui_mainfcn (line 96)
        feval(varargin{:});
Error in new_window_2 (line 42)
    gui_mainfcn(gui_State, varargin{:});
Error in @(hObject,eventdata)new_window_2('pushbutton4_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating uicontrol Callback

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Stephen23 2017-5-29

@Aaron Smith: please edit your question and show us the complete error message. This means all of the red text.

Aaron Smith 2017-5-29

Done. It specifies the line where the error arises. Depending on which push button is used it will either be 116, 153 or 190 as the same line exists in all three

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Answer 1

Jan 2017-5-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/342351-reference-to-non-existent-field-error-occurring#answer_268796

编辑：Jan 2017-6-2

在 MATLAB Online 中打开

As mentioned in your other thread, your code would be much easier to read, if you use the auto-indentation.

The are some bugs in the code. E.g.:

% finishCellB = cell(length(FilesB));   Should be:
finishCellB = cell(1, length(FilesB));

Simplify your code:

if  handles.option == 1                     % If this button is pushed, Bin the corresponding file
    handles = guidata(hObject);
    binnedH = sum(handles.finishCellfull, 2);
    handles.horizontalBin = stairs(binnedH);
    guidata(hObject, handles);
elseif handles.option == 2               % If this button is pushed, Bin the corresponding file
    handles = guidata(hObject);
    binnedH = sum(handles.finishCellhalf, 2);
    handles.horizontalBin = stairs(binnedH);
    guidata(hObject, handles);
else                                         % If this button is pushed, Bin the corresponding file
    handles = guidata(hObject);
    binnedH = sum(handles.finishCellquarter, 2);
    handles.horizontalBin = stairs(binnedH);
    guidata(hObject, handles);
end

Leaner:

handles = guidata(hObject);
if  handles.option == 1
  binnedH = sum(handles.finishCellfull, 2);  
elseif handles.option == 2
  binnedH = sum(handles.finishCellhalf, 2);
else
  binnedH = sum(handles.finishCellquarter, 2);
end
handles.horizontalBin = stairs(binnedH);
guidata(hObject, handles);

Or even:

handles = guidata(hObject);
options = {'finishCellfull', 'finishCellhalf', 'finishCellquarter'};
field   = options{handles.option};
handles.horizontalBin = stairs(sum(handles.(field), 2));
guidata(hObject, handles);

Less code, less chances for typos.

We still cannot run your code and therefore not reproduce the problem. And as in your other thread, I mentione, that you can examine what's going on using the debugger. Set breakpoints in the code and check, where the concerned field is existing and where it is missing. Then it will be a command in between, which has removed the field.

Can you confirm, that the field handles.verticalBin does exist inside the OpeningFcn in line 63? Set a breakpoint in this line to check this.

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Jan 2017-5-29

编辑：Jan 2017-5-29

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@Aaron: This is a very basic question and you can check this very easily by your own:

C = cell(2)
D = cell(1, 2)

Type this in the command window and see, what happens. Do you want to create a {length(FilesB), length(FilesB)} cell matrix? You need to use debugging techniques to see, what's going on. Learn how to obeserve, what Matlab is doing. Otherwise you only guess, what your code does.

I do not even see, where you have created the field verticalBin initially. Are you sure, that is existing at all? If you are sure, why? Did you check it?

And if you add a breakpoint in the line 63, the code fails with an error in the previous line already? Did you create handles.option anywhere? If you later check:

if handles.option == 1

it seems like 'option' contains a number. But in the OpeningFcn you try to enable it:

set(handles.option, 'enable', 'on')

It is bewildering, that your code fails with a completely new problem, when I ask you to debug the mentioned problem. Did you run the code you have posted here? Did it fail before in the OpeningFcn already and you did not detect the problem?

I'm still convinced, that the solution will be very easy. The only difficulty is to determine, where the missing field is removed or finding out, if it was created at all. Using the debugger this is easy and done in some seconds. Unfortunately we cannot do this for you and without the FIG file we cannot run the code. But you can do this by your own. Learn how to use the debugger. Then programming gets a lot easier and efficient.

Jan 2017-5-29

在 MATLAB Online 中打开

If handles.verticalBin is created in the callback of the radio button, how can

set(handles.verticalBin, 'enable', 'off');

run successfully in the OpeningFcn?

If the GUI is started, the figure is created and the OpeningFcn runs. Afterwards the callbacks are called, when their objects are activated.

For me it looks like the field handles.verticalBin is not created before it is used. This should concern horizontalBin also.

If teh contents of handles.verticalBin is "a binned version of the data", why do you try to set its 'Enable' property to 'off'? What exactly is "a binned version"? Is it a handle of a graphics object? If not, does is have an 'enable' property?

You create this in the pushbutton2_Callback:

handles.finishCellhalf = finishCellB{1};

and this in the OpeningFcn:

set(handles.finishCellhalf, 'enable', 'on');

This is strange. What do you think does 'enable', 'on' mean? Did you note, that the other lines in the OpeningFcn do not run for the same resaons?

I still do not get the impression, that you receive my message, that you have to use the debugger to solve the problem.

Set a breakpoint in the main function and step through the code line by line. Then you can identify the problems.

Jan 2017-5-31

在 MATLAB Online 中打开

@Aaron: Matlab is a deterministic system. Variables defined in side a function, exist inside this function only. The list of variables of a function is called "workspace" of this function. If values should be shared with another function, they have to be provided as input or outputs, or e.g. through a shared struct like the "handles" using the guidata method.

GUIDE is a program to create GUIs in figures and the corresponding code for the callbacks. The handles of the objects created in GUIDE are stored automatically in the handles struct using fieldnames defined by something I don't know (I do not use GUIDE because it is not clear enough). I assume tha tag of the object is used. If so, and the axes is called "axes1", than the field handles.axes1 contains the handle of the axes. Then you do not have to write:

Axes1 = handles.Axes1

How did you get this idea? You would create a variables called "Axes1" inside the OpeningFcn, but you do not need it there. This would not have any magic effects to the other functions. There is no magic at all in Matlab. So do not waste time with inventing and asking magic ideas.

Again: You can simply set a breakpoint in the OpeningFcn and try by your own what happens, if you insert or remove this line. You can check the workspaces of the different callback functions and will find out, that creating a variable inside the OpeningFcn concerns the OpeningFcn only. It is another story, if you add a field to the handles struct there. But I do nmot have to explain this - simply try it.

Try to avoid all guessing like:

set(handles.finishCellhalf, 'enable', 'on');

Especially if you are a beginner, guessing how things work in Matlab will file very likely. Follow the examples in the documentation and do not insert some code anywhere which might be useful to do anything anywhere else. Remember that Matlab is the perfect opposite of Pirates of the Carribbean! :-)

Use the debugger to check, which fields are existing in the handles struct. Stop anywhere in the code and type this in the command window:

handles

This is much faster than asking the forum and it reveals all details about this struct.

Jan 2017-6-1

在 MATLAB Online 中打开

@Aaron: I'm confused. Do you get the error "Undefined function or variable 'handles'" or "unknown field axes1"?

Where did you check the contents of the variable "handles"? I've suggested: "Use the debugger to check, which fields are existing in the handles struct. Stop anywhere in the code". So where did you stop? Or did you try this in the command window while the code is not running? Please explain such details. I do not have a crystal ball.

Use the debugger to find the contents of the handles struct: Set a breakpoint in the code, e.g. the OpeningFcn. Let handles = guidata(hObject) run and then check the fieldnames defined in this struct.

 I changes the name of the axes handles in my code from
 handles.Axes1 as I had it to handles.axes1

This is not clear. Where did you apply these changes? Did you check if "axes1" is an existing field?

Do you get my message? It seems like you try to program using erratic guesses of what Matlab does. This will not work. Sit down. Breath. Look at your code. Ask your self: Do I know what Matlab does, when I run this command? Can Matlab know what I want to do?

The same concerns the questions here: Do the readers have enough information to reconsider, what am I doing?

Good luck, Jan

Aaron Smith 2017-6-2

Yeah, I have been opening the figures by clicking on the .fig file. I just tried running it from the code and it works perfectly fine. I am not sure what the problem was

Jan 2017-6-2

As I said: Clicking on a FIG file opens the figure, but does not initialize e.g. the handles struct. Only running the M-file does this.

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