How can I move the vertical line in an axes by a slider within a GUI?

Hi, Guys. I want to change the vertical line position by a slider. The codes as follows.

function slider_wf_Callback(hObject, eventdata, handles)
% hObject    handle to slider_wf (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,'Value') returns position of slider
%        get(hObject,'Min') and get(hObject,'Max') to determine range of slider
global FLAG_DATA_LOADED;
if FLAG_DATA_LOADED == 1
    slider_value = int32(get(hObject,'Value'));
    set(handles.text_cur_frame_num, 'String',num2str(slider_value));
    
    axes(handles.axes_waveform);
    h = vline(slider_value/20, 'r-');
end

guidata(hObject, handles);

However, when I moved the slider, the previous lines still existed. How to solve this problem?Thanks in advance.

Answer 1

[Adam Danz]

Instead of drawing a new line using vline(), draw the line just once and then use the line handle to update its positoin within the slider callback function.

This demo uses xline() instead of the 3rd party vline() function (which isn't a matlab function).

xline() requires >=r2018b

The demo should give you an idea of the code's structure - you can adapt it to your needs.

function slider_wf_Callback(hObject, eventdata, handles)

persistent lineHandle 
if isempty(lineHandle) || ~isvalid(lineHandle)
    % Create line: 1st input is axis handle
    lineHandle = xline(handles.Axes, 0,'r-'); 
end

% Update line position
slider_value = int32(get(hObject,'Value'));
lineHandle.Value = slider_value/20; 

end

*Not tested