Callback functions WindowButtonUpFcn not assigning proper SelectionType when multiple buttons are pressed

Question

Alessio Bernazzi 2022-5-11

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1716200-callback-functions-windowbuttonupfcn-not-assigning-proper-selectiontype-when-multiple-buttons-are-pr

回答： Abhishek Chakram 2023-10-6

I want my program to do the following:

Create a figure and detect when it's been clicked
If it's been left clicked, at the release of the click do a certain action
If, while holding left click, you right click instead, then cancel the action

However when I right click while holding left click, the WindowButtonDownFcn callback doesn't go off and the WindowButtonUpFcn callback instead detects the SelectionType as 'normal' when it should be 'alt'; then it doesn't register the left click release.

Here is a simplified version of the code where there are only the parts relevant to the problem

function test
board = 0;
figure('WindowButtonDownFcn', @choice);
imshow(board);
    function choice(src, ~)
        seltype = src.SelectionType;
        if strcmp(seltype,'normal')
            disp('left click')
            src.WindowButtonUpFcn = @answer;
            %If left clicking, assign the callback for click release to
            %function 'answer'
        elseif strcmp(seltype,'alt')
            disp('right click')
            src.WindowButtonUpFcn = '';
            %If right clicking, reset the callback for click release to
            %null
        end
    end
    function answer(src, ~)
        seltype = src.SelectionType;
        if strcmp(seltype,'normal')
            %If releasing left click, give the answer required
            disp('OK')
        end
    end
end

The outcome is the following:

Press Left Click: all as it should be

Press Right Click: the 'right click' that should show up doesn't

Release Right Click: the 'OK' shows up

Release Left Click: nothing shows up

I'm not sure why the "right click press" instance does not make the program go into the code that should remove the assignment on the WindowButtonUpFcn callback, and I'm even less sure why the right click release gets registered as a left click release.

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Voss 2022-5-11

Verify what the SelectionType actually is when the right-click happens. If the left mouse button is already down, then I believe the right-click comes in as an 'extend' type, not 'alt' type.

DAMIANO YOEME BUSSAGLI 2022-5-11

编辑：DAMIANO YOEME BUSSAGLI 2022-5-11

I had similar problems recently on MATLAB Online.

Trying your code on MATLAB Online (version '9.12.0.1896817 (R2022a)') I get incorrects outputs (exactly as you showed).

But trying the code on desktop (MATLAB version '9.12.0.1927505 (R2022a) Update 1') the outputs are the correct ones:

Press Left Click: disp('left click')
Press Right Click: disp('right click')
Release Right Click: nothing shows up
Release Left Click: nothing shows up

Unfortunately I don't know why this happens, but it should be a problem of MATLAB Online.

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Answer 1

Abhishek Chakram 2023-10-6

在 MATLAB Online 中打开

Hi Alessio Bernazzi.

It is my understanding that you want to create a program that does the following tasks:

Create a figure and detect the clicks on it
If left clicked, do a certain task at the release of the click
If right clicked, while holding left click, cancel the task

Here is a sample code to achieve the same:

% Initialize the click state variables
clc;
global leftClick rightClick
leftClick = false;
rightClick = false;
% Create a figure
hfig = figure();
% Set the WindowButtonDownFcn callback
hfig.WindowButtonDownFcn = @(src, evt) mouseButtonDown(src, evt);
% Set the WindowButtonUpFcn callback
hfig.WindowButtonUpFcn = @(src, evt) mouseButtonUp(src, evt);
% Callback function for left mouse button down
function mouseButtonDown(src, evt)
global leftClick rightClick
    if strcmp(evt.Source.SelectionType, 'normal') % Left click
        leftClick = true;
    elseif strcmp(evt.Source.SelectionType, 'alt') % Right click
        rightClick = true;
    elseif strcmp(evt.Source.SelectionType, 'extend') % Right click
        rightClick = true;
        leftClick = true;
    end
end
% Callback function for left mouse button up
function mouseButtonUp(src, evt)
global leftClick rightClick
    if leftClick && ~rightClick
        % Perform the desired action for left click release
        disp('Left click released');
    elseif leftClick && rightClick
        % Cancel the action for right click
        disp('Right click detected while holding left click');
    end
    
    % Reset the click state variables
    leftClick = false;
    rightClick = false;
end