MATLAB: How to programmatically return focus to a figure after pressing F10 which selects the menu bar in MATLAB 7.9 (R2009b)

MATLAB

As part of a GUI, I would like to use the KeyPressFcn callback to determine the keyboard button that is pressed. However, when I press F10, the figure's menu bar is selected and any further key presses are ignored. The following code demonstrates this issue.

function fig_keypress
% function fig_keypress will create a figure and then  
% report the key pressed in the command widow.
     figure('KeyPressFcn',@cb);
     function cb(src,evnt)
         evnt.Key
     end
  end

Best Answer

The ability to programmatically return focus to the figure is not available in MATLAB 7.8 (R2009a). The F10 key in Windows is reserved for activating the menu bar. Once the F10 key is pressed, the Escape key is needed to deselect the menu. One inelegant workaround is to toggle the visibility of the MenuBar as the following example code demonstrates. This has the unfortunate side-effect of causing the figure to flicker, although the focus is returned to the figure as desired so that future key presses are correctly interpreted.

function fig_keypress
% function fig_keypress will create a figure and then  

% report the key pressed in the command window.

     h = figure('KeyPressFcn',@cb);
     function cb(src,evnt)
         evnt.Key
         if strcmpi(evnt.Key,'f10')
             % toggle MenuBar visibility
             set(h,'MenuBar','none');
             set(h,'MenuBar','figure');
         end
     end
  end
If a custom menu bar is being used, another inelegant workaround is to toggle the visibility of the figure and update the figure with the "drawnow" command. This also has the unfortunate side-effect of causing the figure to flicker. 
function fig_keypress
% function fig_keypress will create a figure and then  
% report the key pressed in the command window.
     h = figure('KeyPressFcn',@cb);
     function cb(src,evnt)
         evnt.Key
         if strcmpi(evnt.Key,'f10')
             % toggle Figure visibility
             set(h,'Visible','off');
             set(h,'Visible','on');
             drawnow;
         end
     end
  end

Related Solutions

MATLAB: In MATLAB R2017a, how to change the focus of the “WindowKeyPressFcn” figure callback function from the command window back to the figure when a key is pressed

This is a known issue, and a potential workaround for this issue in MATLAB R2017a is to create a null figure callback function for "WindowKeyPressFcn" or "KeyPressFcn".

% Example of figure retaining focus when keyboard button is pressed
function KeyPressTest()
    f = figure;
    f.WindowKeyPressFcn = {@testKeyPressFcn};
end
function testKeyPressFcn(source,~)
    disp('Focus Retained')
    source.WindowKeyPressFcn = {@testKeyPressFcnNull};
end
function testKeyPressFcnNull(~,~)
end

MATLAB: Can I execute a specific callback process when I lose the focus of edit text

The callback of the editable text box will be executed when

· the focus moves to another component from the edit text

· with edit text in focus, the enter key (Enter + Ctrl in case of multiple line input support) is entered

There is no callback function that operates only when the focus shifts, but as an alternative, you can use the way which identifying the last key entered in the Callback function. If it is not the "Enter" key, you can define that the focus has shifted.

The sample code below is an example.

In the editable text box Callback function, identify the last entered key using the Figure's CurrentCharacter property. This will change the processing of the callback when pressing the Enter key in the editable text box and moving the focus.

(edit_off_samp.m)
function edit_off_samp
h_figure = figure;
h_edit = uicontrol('Style','edit','Callback',@edit_callback); % create editbox
      function edit_callback(src,event)
      % define callback
          CK = get(h_figure, 'CurrentCharacter'); % get the last key entered
          if isequal(double(CK),13) % If it was "Enter" key
              disp('Pressed Enter Key')
          else
              disp('Focus off')
          end
      end
end

Best Answer

Related Solutions

MATLAB: In MATLAB R2017a, how to change the focus of the “WindowKeyPressFcn” figure callback function from the command window back to the figure when a key is pressed

MATLAB: Can I execute a specific callback process when I lose the focus of edit text

Related Question