只需在handles结构中添加一个新字段sampledistPrev。
在GUI的openingFcn中，使用如下行定义属性：

handles.sampledistPrev = 10; %# or whatever you choose as default value
%# if you want, you can set the default value to the GUI, so that you only need 
%# to change it at one point, if necessary, like so:
set(handles.sampledist,'String',num2str(handles.sampledistPrev));
%# don't forget to save the handles structure at the end of the openingFcn
guidata(hObject,handles)

然后像这样更新回调：

function sampledist_Callback(hObject, eventdata, handles)
% hObject    handle to sampledist (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of sampledist as text
%        str2double(get(hObject,'String')) returns contents of sampledist as a double

input = str2double(get(hObject,'String'));
if(input < 0 || input > 500)
    errordlg('Sampled Dist. must be > 0 and < 500','Sample Dist - Input Error');
    set(handles.sampledist,'String',num2str(handles.sampledistPrev)); %reset value be the previous entry!
    guidata(hObject,handles); %# Note that you don't need to save the handles structure unless
                              %# you have changed a user-defined value like sampledistPrev
                              %# It may still be useful to do it so you always remember
else
   set(handles.sampledist,'String',['',input]);
   %# also update the reset value
   handles.sampledistPrev = input;
   guidata(hObject,handles);
end

为什么不将“先前的值”存储为该对象的“UserData”，如下所示：

function sampledist_Callback(hObject, eventdata, handles)
    input = str2double(get(hObject,'String'));
    if (input < 0 || input > 500)
        errordlg('Sampled Dist. must be > 0 and < 500','Sample Dist - Input Error');
        val=get(hObject,'UserData');
        if isempty(val)
            val='';
        end
        set(hObject,'String',val); %<--- This is where you'd like to set the previous entry value!
        guidata(hObject,handles);
    else
        input=num2str(input);
        set(handles.sampledist,'String',input,'UserData',input);
        guidata(hObject,handles);
    end
end

% Y.T.

作为对这个旧线程的贡献，我修改了最新的脚本（asnwer 2），使其成为一个通用脚本，这样你就可以在任何编辑文本框的回调中使用它。脚本自动检测对象的标记。
通过这种方式，您可以通过直接从uicontrol回调调用此脚本来直接调用此脚本进行数值数据验证。
希望有帮助。
最好的问候。

function Edit_Box_Numeric_Value_Check(hObject, handles)

str = str2double(get(hObject,'String'));
if (isempty(str)||isnan(str))
    warndlg('Input must be a real number','Warning');
    % errordlg('Input must be a real number','Warning');
    val=str2double(get(hObject,'UserData'));
    if (isempty(val)||isnan(val))
        val='';
    end
    set(hObject,'String',val); %<--- This is where you'd like to set the previous entry value!
    guidata(hObject,handles);
else
    str=num2str(str);
    set(eval(sprintf('handles.%s',hObject.Tag)),'String',str,'UserData',str);
    guidata(hObject,handles);
end