MATLAB: How to reuse the context menu for multiple objects

contextMATLABmenumultiplereuseuicontextmenu

I've created a uicontextmenu object, that I want to use with multiple objects in my GUI. How do I program it to recognize which object I clicked on and perform the appropriate action, instead of programming a separate context menu for each object?

Best Answer

The handle of the last object that you right-clicked (to open the context menu) in the figure will be stored in the figure's CurrentObject property. You can access this property directly with the GCO command, or by using GET on the main figure. You can then use the value of this property to determine what to do. Example:

function varargout = contextmenu_Callback(h, eventdata, handles, varargin)
% determine which object was clicked
obj = get(handles.figure,'CurrentObject');
% the following statement is equivalent when used in this context:
% obj = gco; 
switch get(obj,'type')
      case 'axes'
          % code if axes was clicked
      case 'uicontrol'
          switch get(obj,'Style')
              case 'pushbutton'
              % right-clicked a pushbutton
              case 'edit'
              % right-clicked a edit text box
              case 'text'
              % right-clicked a static text box
          end
end

You could also compare the handle for the object to the data stored in the 'handles' structure variable, to determine exactly which object was selected.

Related Solutions

MATLAB: Multiple objects sharing a context menu

This is far too late top be of use to the person asking the question I am sure, but today I had to solve this same problem myself, did an internet search and bizarrely landed here to find my own suggestion which I hadn't even considered when thinking about a solution to this before my search today. So I have now implemented my idea and since it is just a general wrapper type class without any proprietary code I will add my solution here.

It may be there is some simpler way that both myself and the original asker of the question both missed, but even if there is, I enjoyed creating my own solution anyway!

classdef GraphicsObjectWithContextMenu < handle
  
  properties( SetAccess = immutable, GetAccess = private )
    hGraphics = [];
    
    hContextMenu = matlab.ui.container.ContextMenu.empty;
  end
  
  methods
    function obj = GraphicsObjectWithContextMenu( hGraphics )
      assert( isgraphics( hGraphics ), 'GraphicsObjectWithContextMenu:InvalidGraphicsObject', 'hGraphics must be a handle to a valid graphics object' );
      
      obj.hGraphics = hGraphics;
      
      obj.hContextMenu = uicontextmenu( );
      obj.hGraphics.UIContextMenu = obj.hContextMenu;
    end
    
    function addMenuItem( obj, menuItem, callback )
      validateattributes( menuItem, { 'matlab.ui.container.Menu' }, { 'scalar' } )
      validateattributes( callback, { 'function_handle' }, { 'scalar' } )
      assert( nargin( callback ) == 1, 'GraphicsObjectWithContextMenu:InvalidMenuCallback', 'callback must be a function handle of exactly 1 argument, representing the graphics object to which the context menu is attached' );
      
      menuItem.Parent = obj.hContextMenu;
      
      fCallback = @( src,evt ) callback( obj.hGraphics );
      menuItem.Callback = fCallback;
    end
  end
  
end

is the class I mentioned in the comments to the question. I had to put a little thought in to its structure as my original quickly thrown out suggestion didn't fully consider all the difficulties. Also this is not the only way to setup this class of course, it is just the way that I am happy with for my work.

Obviously some aspects of it are optional, but I like to validate things in my classes and assert where I consider it appropriate too for ease of usage, but that is just my preference - it is not crucial to the bare minimum solution.

And here is some simple example code to show it in use with multiple line objects. I just added one menu item to the context menu as it is the only one I need for my current work, but others can be added in just the same manner.

figure; hAxes = gca;
hold on
hLines(1) = plot( hAxes.XLim, [2 2], 'LineWidth', 2 );
hLines(2) = plot( hAxes.XLim, [3 3], 'LineWidth', 2 );
hLines(3) = plot( hAxes.XLim, [7 7], 'LineWidth', 2 );
hLines(4) = plot( hAxes.XLim, [8 8], 'LineWidth', 2 );
m1 = uimenu( 'Label', 'Remove' );
linesWithContextMenu = GraphicsObjectWithContextMenu.empty( 0, numel( hLines ) );
for n = 1:numel( hLines )
  linesWithContextMenu( n ) = GraphicsObjectWithContextMenu( hLines( n ) );
  linesWithContextMenu( n ).addMenuItem( m1.copy( ), @( lineHandle ) delete( lineHandle ) );
end

The key points of the solution are:

The handle-derived class allows you to wrap up an individual graphics object handle together with a context menu so that the context menu knows its triggering graphics object
The menu items have been added via a function which takes the callback as a separate argument to the menuItem in which it would normally live. This you can see is because the callback should have 1 variable argument, the graphics object handle, which this class function fills in to create the actual callback which the menu item will trigger. This means that your callback function can be anything you want that works with the handle of the graphics object that triggered the callback.
Usage should be very simple, but beware to take a copy of the menu item object when adding it to multiple objects, otherwise the same item will just keep getting re-parented and only the last object it is assigned to will actually have the context menu item.

MATLAB: How to make a push button respond to clicking with the right mouse button

There are two properties which can be used in conjunction to accomplish this.

One is the button's 'ButtonDownFcn' callback function. This callback function executes when pressing a mouse button on or near a UICONTROL object -- including when pressing the right mouse button.

The other property is the figure's 'SelectionType' property. This property indicates which kind of click was registered in the figure window -- including clicks on controls within the figure.

Putting these two together, you can define a 'ButtonDownFcn' callback for a push button which checks the figure's 'SelectionType' property to detect a right-click. An example is shown below. (In that example, the ANCESTOR function is used to get the figure's handle. If this is being done in a GUIDE-created GUI, this is unnecessary as the 'handles' structure already provides access to the figure's handle.)

function test
      uicontrol('Style', 'pushbutton', ...
                'ButtonDownFcn', @myCallback);
end
function myCallback(src, evt)
      figHandle = ancestor(src, 'figure');
      clickType = get(figHandle, 'SelectionType');
      if strcmp(clickType, 'alt')
          disp('right click action goes here!');
      end
end

Best Answer

Related Solutions

MATLAB: Multiple objects sharing a context menu

MATLAB: How to make a push button respond to clicking with the right mouse button

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