MATLAB: Prompting Error for user input

errodlg

Suppose I have a input box that requires an entry greater than zero before attempting to load a file.
function test_Callback(hObject, eventdata, handles)
  test = str2double(get(hObject, 'String'));
if isnan(test)
    set(hObject, 'String', 0);
    errordlg('Input must be a number','Error');
end
handles.backup.test= test;
guidata(hObject,handles)
function loaddata_Callback(hObject, eventdata, handles)
      test_Callback(hObject, eventdata, handles)
[filename, pathname, Index] = ...
     uigetfile({'*.txt';},['Select the File to load'],...
        '\\MyDocuments\User');
This prompts the error "'Input must be a number','Error'' and allows the user to open and search for this file. What am I doing wrong?

Best Answer

You need to put this
    test = str2double(get(hObject, 'String'));
    if isnan(test)
        set(hObject, 'String', 0);
        errordlg('Input must be a number','Error');
    end
in a loop and not leave the loop until you have a legal value from the user.
BTW: I think it is a good habit to close functions with "end".
.
A detail: change
    set(hObject, 'String', 0);
to
    set(hObject, 'String', '0' );
.
An example according to my originally answer. This code gives the user ten chances to enter a correct value.
    function test_Callback(hObject, eventdata, handles)
        for ii = 1 : 10
            test = str2double(get(hObject, 'String'));
            if isnan(test)
                set(hObject, 'String', 0);
                errordlg('Input must be a number','Error');
            elseif gt(test,1)
                handles.backup.test = test;
                guidata(hObject,handles);
                break
            elseif  gt(1,test)
                set(hObject, 'String', '0');
                errordlg('Input must be greater than 0','Error');
            end
        end
    end
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