MATLAB: Reading Arrow Key Input

arrow keysinputkeyboardkeypressfcn

What I'm basically trying to do is control a robot by using the arrow keys on the keyboard. I'm already familiar with outputting commands via MATLAB my main problem is how to read what arrow keys I'm pressing. Ultimately I would like to press an arrow button and have it displayed on the command window.

I came across this bit of code online. It works great but I need the keystrokes to be store in a variable (possibly as a number instead of a string) so I can output it. There may be a simple solution but since I don't really understand the code my attempt to edit it didn't work.

h_fig = figure;
set(h_fig,'KeyPressFcn',@(h_obj,evt) disp(evt.Key));

Thank You

Sayyid Khan

Best Answer

Here is an example of how to use the arrow keys in the keypressfcn.

function [] = move_fig()
% move figure with arrow keys.
S.fh = figure('units','pixels',...
              'position',[500 500 200 260],...
              'menubar','none',...
              'name','move_fig',...
              'numbertitle','off',...
              'resize','off',...
              'keypressfcn',@fh_kpfcn);
S.tx = uicontrol('style','text',...
                 'units','pixels',...
                 'position',[60 120 80 20],...
                 'fontweight','bold'); 
guidata(S.fh,S)             
function [] = fh_kpfcn(H,E)          
% Figure keypressfcn
S = guidata(H);
P = get(S.fh,'position');
set(S.tx,'string',E.Key)
switch E.Key
    case 'rightarrow'
        set(S.fh,'pos',P+[5 0 0 0])
    case 'leftarrow'
        set(S.fh,'pos',P+[-5 0 0 0])
    case 'uparrow'
        set(S.fh,'pos',P+[0 5 0 0])
    case 'downarrow'
        set(S.fh,'pos',P+[0 -5 0 0])
    otherwise  
end

EDIT

% This assigns the string value of the key to a in the base workspace.
set(h_fig,'KeyPressFcn',@(H,E) assignin('base','a',E.Key));

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MATLAB: GUI flickers when customly resized

I think your approach looks like what I have done in the past. I tried to do a couple of things which I think might make a slight difference in speed, but perhaps not. (Some things I changed just to help me understand the code.)

One thing I did notice was this setFocusFig function. When I comment out the call to that, the GUI does seem to resize smoother. I wonder what the purpose of this function is? The only thing that I can see it doing is making the callback object lose focus after the resize. Anyway, I doubt this will help, but give it a try. It is difficult for me to do much without seeing the flickering that you are.

function S = example3()
% Figure Window
S.fh = figure('Units','pixels','Pos',[600 500 370 225],...
              'Menubar','none','Resize','off');
% Uipanel for buttons
S.upB = uipanel('Title','Show buttons','Units','pixels','Pos',[10 90 351 65]);
% Buttons check box
S.cbB = findall(S.upB,'style','text');
set(S.cbB,'Style','checkbox','Parent',S.fh,'Visible','on','userd',S.upB,...
            'Value',1,'Pos',[20 148 90 15],'Callback',{@cb_call});
% Uipanel for stats
S.upS = uipanel('Title','Show stats','Units','pixels','Pos',[10 10 351 65]);
% Stats check box
S.cbS = findall(S.upS,'style','text');
set(S.cbS,'Style','checkbox','Parent',S.fh,'Visible','on','userd',S.upS,...
            'Value',1,'Pos',[20 68 90 15],'Callback',{@cb_call});
% textbox
S.txDisp  = uicontrol('Style','text','Pos',[10 170 200 55]);
S.txComp  = uicontrol('Style','text','Pos',[225 178 115 33]); 
% cb_call -----------------------------------------------------------------
    function cb_call(varargin)
        H = varargin{1};
        P = get(H,'userd');  % The uipanel it is connected to.
        if get(H,'Value')
            resizeFig(get(P,'Pos') - 5,H,S.cbB,S.upB,S.txComp,S.txDisp)
            set(P,'Visible','on');
        else
            resizeFig(5 - get(P,'Pos'),H,S.cbB,S.upB,S.txComp,S.txDisp)
            set(P,'Visible','off');            
        end
%           setFocusFig(H)  % What is this for??
      end
% resizeFig ---------------------------------------------------------------
    function resizeFig(varargin)
        H = varargin{1}(4);
        set(S.fh,'Pos', get(S.fh,'Pos') + [0 -H 0 H])
        for h = unique([varargin{2:end}])
            set(h,'Pos', get(h,'Pos') + [0 H 0 0])
        end
    end
% setFocusFig -------------------------------------------------------------
    function setFocusFig(hObject)
        % Workaround to set focus to figure
        set(hObject, 'Enable', 'off');
        drawnow;
        set(hObject, 'Enable', 'on'); 
    end
end

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

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

Best Answer

Related Solutions

MATLAB: GUI flickers when customly resized

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

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