Confusing interaction between "Callback" and "KeyPressFcn" for "edit"-style UIControl

Hello --

I'm having difficulty understanding an interaction between a "Callback" and "KeyPressFcn" in my figure- and uicontrol-based tool.

I have an "edit"-style uicontrol with both a "KeyPressFcn" and "Callback" defined. The "Callback" initiates an input validation sequence and is working as intended. I want the "KeyPressFcn" to perform a pseudo-autocomplete as defined here. Here's a minimal version of what I have:

% Initial setup ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

% Set allowed strings
str = ["FOO", "BAR", "BAZ", "QUX", "FOOBAR", "BAZQUX", "FARBOO"];

% Set up figure
f = figure;
e = uicontrol('Style', 'edit', 'String', str(3), 'Callback',  @cb, ...
    'KeyPressFcn', @kp, 'Interruptible', 'off', 'BusyAction', 'queue');

% Set up guidata
data.AllowedStrings = str;          % Store allowed strings
data.EditBoxString = e.String;      % Store a copy of the current string
data.AutoComplete.String = [];      % Autocomplete: initial string
data.AutoComplete.Counter = 1;      % Autocomplete: which completion are we on?
data.AutoComplete.Options = [];     % Autocomplete: List of possible completions
guidata(f,data)

% Functions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

% Callback: Data Validation
function cb(src,~)

    % Get guidata
    data = guidata(src);

    % Check supplied string against valid strings
    val = erase(lower(src.String), [" ", ":", "-", "(", ")"]) == ...
        lower(data.AllowedStrings);

    % If invalid, reset the string to its previous value and return
    if ~nnz(val)
        src.String = data.EditBoxString;
        return
    end

    % Set editbox string to validated string and repack data
    src.String = data.AllowedStrings(val);
    data.EditBoxString = data.AllowedStrings(val);
    guidata(src,data)
        
end

% KeyPressFcn: "Autocomplete" on leftbracket push
function kp(src,k)

    % Get guidata
    data = guidata(src);

    % Autocomplete if "leftbracket" was pressed
    if k.Key == "leftbracket"

        % Get autocomplete string if none exists
        if isempty(data.AutoComplete.String)
            data.AutoComplete.String = erase(lower(src.String), ...
                ["["," ", ":", "-", "(", ")"]);
        end

        % Get possible completions using "startsWith"
        data.AutoComplete.Options = find(startsWith(...
            lower(data.AllowedStrings), data.AutoComplete.String));

        % Fill text with next possibility
        if ~isempty(data.AutoComplete.Options)

            % Set string
            src.String = data.AllowedStrings(...
                data.AutoComplete.Options(data.AutoComplete.Counter));

            % Iterate counter
            data.AutoComplete.Counter = mod(data.AutoComplete.Counter, ...
                length(data.AutoComplete.Options)) + 1;
        end

    else

        % Set autocomplete string to empty & reset counter
        data.AutoComplete.String = [];
        data.AutoComplete.Counter = 1;
        data.AutoComplete.Options = [];

    end

    % Repack guidata
    guidata(src,data)
        
end

This does not seem to work. However, if I place a breakpoint on lines 25 (data = guidata(src) in the cb function) and 54 (if isempty(data.AutoComplete.String) in the kp function) and use F5 / F10 to sequentially complete each function, it works exactly as intended! I'm able to supply an input, say "b", then repeatedly press "[" to cycle through the relevant options: "BAR", "BAZ", and "BAZQUX". I just need to roll forward through all the breakpoints before I press "[" again.

This "almost-right" behavior is dependent on the "Interruptible" property being set to "off", so I imagine it's due to some subtlety in when the "Callback" is executed; it's just baffling to me that everything is (or appears to be) working in the right order when I include breakpoints but not without them. I think I need my "Callback" never to execute while I'm cycling through my autocomplete options.

Any suggestions? I'd prefer not to migrate the edit box into the more modern UI elements if possible.

Thanks!

[Stephen23]

"I want the "KeyPressFcn" to perform a pseudo-autocomplete as defined here. "

It will not work as you want. That answer is unrealistically optimistic.

"Any suggestions?"

There is no way to reliably obtain/update the text, until the user presses ENTER or clicks away from the box.

"I'd prefer not to migrate the edit box into the more modern UI elements if possible."

I was in a similar situation with this function, which previously relied on some ugly keypress hack to work:

https://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-tool

Then I discovered that UITEXTAREA and UIEDITFIELD (and possibly others) provide a VALUECHANGINGFCN callback, which triggers on every content change in real time. This callback makes tracking user inputs much simpler than any train-wreck-keypress-hack. I recommend that you reconsider your restriction: there is quite possibly the functionality that you require to support your expected workflow.

[Aaron]

Thanks for your thoughts. I do think the ValueChangingFcn field of the EditFields would solve this issue quite handily.

I'm torn on moving my tool over still because of some lost functionality from the old UI functions, particularly the "normalized" units and a lack of visual customization options (e.g. why can I change a "Foreground" and "Background" color but not the color of scroll bars and UI tab selectors?).

[Stephen23]

"...particularly the "normalized" units"

I know exactly where you are coming from, I had exactly the same fight with the function IREGEXP: specifying UI element sizes was a complete pain as everything is in terms of pixels. Resizing all of the UI elements was an awkward, complex, fiddly task...

Until I discovered UIGRIDLAYOUT.

Only then did UIFIGURE resizing make sense.

Forget about normalized units. Forget about setting the UI element sizes yourself. With UIFIGUREs trying to set the UI element sizes yourself only causes code bloat and loss of hair. In contrast, with UIGRIDLAYOUT it is simple and quite intuitive: it lets you specify absolute sizes, normalized sizes, and lots more. I recommend giving it a try.

When I rewrote IREGEXP (motivated by the irreplaceable VALUECHANGINGFCN) I made a false start by trying to specify the element sizes myself (i.e. as a minimal rewrite of the original FIGURE-based GUI). Bad idea. Finding UIGRIDLAYOUT meant that I very quickly rewrote the relevant code and bingo! Easier and better.

"...a lack of visual customization options"

I have not tried such color properties, so cannot comment.

[Aaron]

Hi Stephen,

Thanks again for your insights. I'll likely be returning to your iregexp code as an example for uifigure in the future.

I also chanced on uigridlayout when I was planning my current project, but have already written my own bespoke grid layout function which allows a "paint-by-numbers"-style Excel sheet to define a grid layout in "normalized" units. This is of course probably a worse implementation of whatever uigridlayout does behind the scenes, but it's fun to use and lets me visually edit the grid in familiar software.

I actually was able to get my autocomplete working exactly as intended with "KeyPressFcn"; see my answer for the functional code. I just needed to add a step to unfocus and focus the text box every time it autocompletes.

Answer 1

[Aaron]

With @Walter Roberson's note that the "String" property of an "edit"-style uicontrol can't be visually updated without the box losing focus, I was able to modify the code to properly autocomplete.

I did this by adding an additional dummy uicontrol and toggling focusing between the two at the beginning of the autocomplete procedure.

Working autocomplete code:

% Initial setup ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

% Set allowed strings
str = ["FOO", "BAR", "BAZ", "QUX", "FOOBAR", "BAZQUX", "FARBOO", "QUAIL", "QIT"];

% Set up figure
f = figure;
e1 = uicontrol('Style', 'edit', 'String', str(3), 'Callback',  @cb, ...
    'KeyPressFcn', @kp, 'Interruptible', 'off', 'BusyAction', 'cancel', 'Tag', 'e1');
e2 = uicontrol('Style', 'edit', 'Position', [200, 200, 100, 100], 'Tag', 'e2');

% Set up guidata
data.AllowedStrings = str;          % Store allowed strings
data.EditBoxString = e1.String;      % Store a copy of the current string
data.AutoComplete.String = [];      % Autocomplete: initial string
data.AutoComplete.Counter = 1;      % Autocomplete: which completion are we on?
guidata(f, data);

% Functions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

% Callback: Data Validation
function cb(src, ~)

    % Get guidata
    data = guidata(src);

    % Check supplied string against valid strings
    val = erase(lower(src.String), [" ", ":", "-", "(", ")"]) == ...
        lower(data.AllowedStrings);

    % If invalid, reset the string to its previous value and return
    if ~nnz(val)
        src.String = data.EditBoxString;
        return;
    end

    % Set editbox string to validated string and repack data
    src.String = data.AllowedStrings(val);
    data.EditBoxString = data.AllowedStrings(val);
    guidata(src, data);

end

% KeyPressFcn: "Autocomplete" on leftbracket push
function kp(src, k)

    % Get guidata & handles
    data = guidata(src);
    hndl = guihandles(src);

    % Autocomplete if "leftbracket" was pressed
    if k.Key == "leftbracket"

        % Unfocus and focus to fix the issue!
        uicontrol(hndl.e2)
        uicontrol(hndl.e1)

        % Get autocomplete string if none exists
        if isempty(data.AutoComplete.String)
            data.AutoComplete.String = erase(lower(src.String), ...
                ["[", " ", ":", "-", "(", ")"]);
        end

        % Get possible completions using "startsWith"
        data.AutoComplete.Options = find(startsWith(...
            lower(data.AllowedStrings), data.AutoComplete.String));

        % Set string
        if ~isempty(data.AutoComplete.Options)

            % Set string
            src.String = data.AllowedStrings(...
                data.AutoComplete.Options(data.AutoComplete.Counter));

            % Iterate counter
            data.AutoComplete.Counter = mod(data.AutoComplete.Counter, ...
                length(data.AutoComplete.Options)) + 1;
            
        end
    else
        % Set autocomplete string to empty & reset counter
        data.AutoComplete.String = [];
        data.AutoComplete.Counter = 1;
    end
        % Repack guidata
        guidata(src, data);
end

Answer 2

[Walter Roberson]

Changing the String property of a uicontrol is not reflected on the display until the user presses Enter or moves the focus away from the control. The String property changes, but the display is not updated. Therefore, you will not be able to do pseudo autocomplete without the user continually pressing enter or clicking elsewhere.

[Aaron]

Thanks, this is helpful.

Couldn't I then programmatically unfocus & focus the control after each autocomplete? It doesn't follow to me from this info that what I'm trying to do is impossible.

[Walter Roberson]

If you unfocus and refocus then you lose the internal positioning of the cursor for the cases where the user edits in the middle of a string.

[Aaron]

If I'm cycling through autocomplete options, I don't particularly care if my cursor has been reset, since the text has been edited upon autocompletion.

I would be happy enough to make that concession, but it seems like the behavior is still not functioning as expected.