MATLAB: How to use the “ButtonDownFcn” for a plot in App Designer

appbuttondownfcncallbackclickdesignerplotuiaxes

Best Answer

You are correct that there is no "ButtonDownFcn" for a UIAxes. Thus, stick to using the "ButtonDownFcn" with your plot object.

To start, create a plot in your app's StartupFcn and define the plot's "ButtonDownFcn" with an associated callback function:

https://www.mathworks.com/help/matlab/creating_plots/button-down-callback-function.html

The key here is _where _you define this callback function. If you simply add a new public/private function in Code View, the plot object will be unable to find the function when the callback is triggered, and you will get an error. This is because your app is set up as a class in App Designer, and thus, your callback will be defined as a class method, not an ordinary function.

The easiest alternative is to define your callback function as a nested function, located inside the StartupFcn. Check out the example below, in which I plot a parabola. If a user clicks on the parabola, a nested callback will be triggered that adds the x- and y-coordinates to a UITable, which lists the coordinates of all points that have been clicked so far.

function startupFcn(app)

    % create plot with line object
    x = linspace(-5,5);
    y = -1 * x.^2;
    plot(app.UIAxes,x,y,'ButtonDownFcn',@mouse_click);
    % define callback as nested func        
    function mouse_click(~,eventData)
        % get coordinates of click 
        coords = eventData.IntersectionPoint;
        % do something with the coordinates (e.g. add coordinates to table)
        app.UITable.Data(end+1,:) = [coords(1),coords(2)];
    end

end

To create run this example yourself, simply add a UIAxes and a UITable to your figure in the Design View of App Designer. Then add the code above to a StartupFcn.

Also, for an alternative method of getting clicked points, see this related MATLAB Answers post:

https://www.mathworks.com/matlabcentral/answers/458264-using-windowbuttondownfcn-in-app-designer

Related Solutions

MATLAB: How do i determine if the uiaxes toolbar is active

Hi,

I suggest using 'SelectionChangedFcn' callback. This is notified whenever a state button(zoom/pan) is clicked, and you can know which button is clicked. You can also write your custom MATLAB code in the callback associated.

Refer the documentation link for more details:

https://in.mathworks.com/help/matlab/ref/axtoolbar.html

MATLAB: How to disable the WindowButtonDownFcn callback when panning/zooming in App Designer

For ordinary figures, ButtonDown callbacks are disabled when zoom/pan are selected. However, this is not the case for UIFigures in App Designer, which is why you are running into an issue.

One way to restrict how often the button click callback is triggered is to restrain the clicks to just the line plot itself. You can do this by setting the "ButtonDownFcn" of your plot object when you first create it:

https://www.mathworks.com/help/matlab/creating_plots/button-down-callback-function.html

Try creating a plot in the app's StartupFcn, then defining a ButtonDown callback as a nested function within that same StartupFcn. With the ButtonDownFcn callback, clicks will only be recorded if the user touches the plot line itself.

Next, we need to disable the ButtonDownFcn callback any time an AxesToolbar button (like pan or zoom) is turned on.

To detect whether a toolbar button has been selected, you can use the "SelectionChangedFcn" callback for an AxesToolbar object:

https://www.mathworks.com/help/matlab/ref/matlab.graphics.controls.axestoolbar-properties.html#mw_d1eae674-733c-43b8-9149-2bf4481a3640_sep_mw_5013a85f-c8fe-4db1-b61f-ad6bb13c6757

This callback will be triggered any time you click zoom/pan. Within this callback you can check two things:

1) If the selected button is "on", then delete your plot object's ButtonDownFcn callback. This will prevent clicks on the line from being recorded.

https://www.mathworks.com/help/matlab/ref/matlab.ui.controls.toolbarstatebutton-properties.html#mw_929a634b-3a90-4a23-b147-ab213d3d3029

2) If the selected button is "off", restore the plot object's ButtonDownFcn callback, so that clicks are once again recorded.

I have implemented all this in the StartupFcn of the attached MLAPP file. I have also included output statements to note when a click is being registered and when a toolbar button is being selected/deselected.

For convenience, I am also pasting the code from my StartupFcn below:

function startupFcn(app)

      % plot some data
      x = 1:5; y = 1:5;
      p = plot(app.UIAxes,x,y,'ButtonDownFcn',@line_click);
      % set up callback for toolbar
      app.UIAxes.Toolbar = axtoolbar(app.UIAxes,{'zoomin','zoomout','pan','datacursor'},...
                      'SelectionChangedFcn',{@tbar_change,p});
      % define callbacks as nested functions
      function line_click(~,~)
        disp('click!');
      end
      function tbar_change(~,event,p)
        state = event.Selection.Value; % ToolBarStateButton has a "Value of "on" or "off"
        % if selected, turn off line_click callback
        if state == 'on'
          disp('toolbar button selected; callback turned off');
          p.ButtonDownFcn = [];
        % if not selected, turn back on line_click
        else
          disp('toolbar button de-selected; callback turned back on');
          p.ButtonDownFcn = @line_click;
        end
      end
    end

Best Answer

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MATLAB: How do i determine if the uiaxes toolbar is active

MATLAB: How to disable the WindowButtonDownFcn callback when panning/zooming in App Designer

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