Why is the uieditfield ValueChangingFcn function called twice?

To get to know app designer I attempted to create an autocomplete thingy when using a uieditfield. The code is provided below as clear as I could. I cannot discover what's wrong with the code, but it's not working as expected and the callback function is called twice. When I put breakpoints in the callback function, it works as I expect it to (even though it's called twice), but without using breakpoints it doesn't. If I type anything in the uieditfield, then click somewhere else (shift focus), then continue typing in the uieditfield, that's when it gives the autocomplete for the previous value. I'm at a loss, does anyone understand?

clear, clc, close all

% Create figure
fig = uifigure;

% List of names
names = {'Bob';
         'Eric';
         'John';
         'Phil';
         'James';
         'Anne';
         'Suzanne';
         'Karen';
         'Eleanor';
         'Janet';};

% Create table of names
namesTablePos = [28 28 504 203];
namesTable = uitable(fig, ...
    'Position', namesTablePos, ...
    'ColumnName', 'Names', ...
    'Data', names);

% Create editfield
fieldPos = [224, 315, 150, 25];
field = uieditfield(fig, 'text', ...
    'ValueChangingFcn', @(h,e) callbackAutoComplete(h,e), ...
    'Position', fieldPos);
field.UserData = names;

% Create tree
tree = uitree(fig, ...
    'SelectionChangedFcn', @(h,e) callbackSelectionChanged(h,e), ...
    'Visible', 'off');

function callbackAutoComplete(src, ~)

    % Get figure handle
    tree = src.Parent.Children(1);

    % Reset tree
    tree.Visible = 'Off';
    delete(tree.Children)

    % Get field value
    val = src.Value; 

    % If value is not empty, populate tree
    if ~isempty(val)

        % Get names
        names = src.UserData;

        % Filter names
        indices = [];
        for ix = 1:numel(names)
            name = names{ix};        
            if contains(lower(name), lower(val))
                indices = [indices ix];
            end
        end

        % Set maximum visible suggestions
        n = min(numel(indices), 3);

        % If any, create nodes
        if n > 0

            % Set tree properties
            fieldPos = src.Position;
            treePos = fieldPos + fieldPos(4).*[0 -n 0 (n-1)];
            tree.set(...
                'Position', treePos, ...
                'Visible', 'on');

            % Add nodes
            names = sort(names(indices));
            for ix = 1 : numel(names)
                uitreenode(tree, 'Text', names{ix});
            end

        end                

    end

end
function callbackSelectionChanged(src, ~)

    % Get node value
    val = src.SelectedNodes.Text;

    % Set value to field
    src.Parent.Children(2).Value = val;

end

Answer 1

[Mario Malic]

Hey Anais,

That's some nice usage of tree component, thanks for that!

Here are two lines that you need to change in your code. If you inspect the src.Value, it does not populate the value unless the focus is shifted away from the component, so it's better to use event.Value since it uses the values you expected.

function callbackAutoComplete(src, event)
val = event.Value;

Here's your code posted with these two lines so the answer is clear for someone else who may encounter this.

clear, clc, close all
% Create figure
fig = uifigure;
% List of names
names = {'Bob';
         'Eric';
         'John';
         'Phil';
         'James';
         'Anne';
         'Suzanne';
         'Karen';
         'Eleanor';
         'Janet';};
% Create table of names
namesTablePos = [28 28 504 203];
namesTable = uitable(fig, ...
    'Position', namesTablePos, ...
    'ColumnName', 'Names', ...
    'Data', names);
% Create editfield
fieldPos = [224, 315, 150, 25];
field = uieditfield(fig, 'text', ...
    'ValueChangingFcn', @(h,e) callbackAutoComplete(h,e), ...
    'Position', fieldPos);
field.UserData = names;
% Create tree
tree = uitree(fig, ...
    'SelectionChangedFcn', @(h,e) callbackSelectionChanged(h,e), ...
    'Visible', 'off');
function callbackAutoComplete(src, event)
    % Get figure handle
    tree = src.Parent.Children(1);
    % Reset tree
    tree.Visible = 'Off';
    delete(tree.Children)
    % Get field value
    val = event.Value;
    % If value is not empty, populate tree
    if ~isempty(val)
        % Get names
        names = src.UserData;
        % Filter names
        indices = [];
        for ix = 1:numel(names)
            name = names{ix};        
            if contains(lower(name), lower(val))
                indices = [indices ix];
            end
        end
        % Set maximum visible suggestions
        n = min(numel(indices), 3);
        % If any, create nodes
        if n > 0
            % Set tree properties
            fieldPos = src.Position;
            treePos = fieldPos + fieldPos(4).*[0 -n 0 (n-1)];
            tree.set(...
                'Position', treePos, ...
                'Visible', 'on');
            % Add nodes
            names = sort(names(indices));
            for ix = 1 : numel(names)
                uitreenode(tree, 'Text', names{ix});
            end
        end                
    end
end
function callbackSelectionChanged(src, ~)
    % Get node value
    val = src.SelectedNodes.Text;
    % Set value to field
    src.Parent.Children(2).Value = val;
end

[Anais G]

Hi Mario, thanks for the answer, that's it! I didn't realize src.Value works like that because of course when I inspected the code the focus got shifted. I think I should read into the differences between src and event input.

Have a nice day!

EDIT: by any chance, do you know why the callback ran twice?

[Mario Malic]

I think it's due to the callback being defined as an anonymous function but I am not sure. If you create an anonymous function and put a breakpoint on it, it'll ask you where do you want to set it IIRC.

I think there's one workspace where the arguments are sent in the anonymous function, and the second is the actual workspace of the function, but you should verify this yourself, as I haven't dug deeply into it.

Have a great day as well!