Visibility of several plot in the same axes by checkmark in GUI

I'm preparing a gui with 2-30 plots where the visibility is controlled by individual checkmark selections. The code is working perfectly when I show two plots in different axes (see gui below)

But if I want to show the two plots in the same axes (axes1) I get this error:

Error using matlab.graphics.chart.primitive.Line/set
Invalid or deleted object.

Error in test>checkbox1_Callback (line 93)
       set(handle_plot1, 'visible' , 'on')

What am I doing wrong?

Here is my code:

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
X1=[1 2 3 4];
Y1=[-1 -2 -3 -4];
X2=[1 2 3 4];
Y2=[1 2 3 4];
set(gca, 'NextPlot', 'add');   % Equivalent to: hold('on')
handles.handle_plot1 = plot(X1,Y1,'visible','off','LineWidth',2,'color', [0 0 0],'linestyle', '--','parent',handles.axes1);
handles.handle_plot2 = plot(X2,Y2,'visible','off','LineWidth',2,'color', [1 0 0],'linestyle', '--','parent',handles.axes1);
guidata(hObject, handles);

% --- Executes on button press in checkbox1.
function checkbox1_Callback(hObject, eventdata, handles)
   handle_plot1 = handles.handle_plot1
   if (get(hObject,'Value')) == 1 
       set(handle_plot1, 'visible' , 'on')
   else 
       set(handle_plot1, 'visible' , 'off')
   end

% --- Executes on button press in checkbox2.
function checkbox2_Callback(hObject, eventdata, handles)
   handle_plot2 = handles.handle_plot2
   if (get(hObject,'Value')) == 1  
       set(handle_plot2, 'visible' , 'on')
   else 
       set(handle_plot2, 'visible' , 'off')

Answer 1

[Jan]

Now try:

set(handles.axes1, 'NextPlot', 'add');  % Not "gca" as in my last suggestion
handles.handle_plot1 = plot(X1,Y1,'visible','off','LineWidth',2, ...
                            'color', [0 0 0],'linestyle', '--', 'parent', handles.axes1);
handles.handle_plot2 = plot(X2,Y2,'visible','off','LineWidth',2, ...
                            'color', [1 0 0],'linestyle', '--', 'parent', handles.axes1);
guidata(hObject, handles);

By the way: I use a specific function to create the 'on', 'off' dynamically:

function S = OnOffStr(D)
OffOn = {'off', 'on'};
L     = (D ~= 0) + 1;  % 0/FALSE => 1, anything else => 2
if length(L) == 1
  S = OffOn{L};   % Reply a string
else
  S = OffOn(L);   % Reply a cell string
end

Then the callback looks like:

function checkbox1_Callback(hObject, eventdata, handles)
set(handles.handle_plot1, 'Visible', OnOffStr(get(hObject,'Value')));

[JB]

That is brilliant. Thanks a lot Jan Simon.