\r\nRecently on two different occasions, people have asked me to help debug their nested function< code. I was struck by the similarity of their problems and today will show you the problem and some solutions.\r\n<\/p>\r\n
\r\n\r\nThe problem, simply stated, is this. The users wrote GUIs using nested functions and brought up a single instance which ran fine. Then they brought up a second instance while the first one was running, and ran the second one. So far, so good. Then each user went to the original GUI window and pushed a button. To the surprise of those watching, the action all happened in the second GUI from that moment forward, regardless of which GUI's button was pressed. What was happening?\r\n<\/p>\r\n
\r\nThe users each wrote GUIs using code with this sort of code structure.\r\n<\/p>\r\n\r\n
\r\nfunction myGUI\r\n \r\nglobal hLines hColor\r\nhfig = figure('name','Changing line colors');\r\nhax = axes('parent',hfig);\r\ninit();\r\n \r\n function init(varargin)\r\n hLines = plot(hax,magic(3));\r\n hColor = uicontrol('style','pushbutton',...\r\n 'string', 'Change line colors', ...\r\n 'units','normalized',...\r\n 'position',[0.01 0.01 0.25 0.05],...\r\n 'callback',@changeColor);\r\n end\r\n \r\n function changeColor(varargin)\r\n colors = {rand(1,3); rand(1,3); rand(1,3)};\r\n set(hLines, {'Color'}, colors);\r\n end\r\nend\r\n<\/pre>\r\n\r\nNotice that some of the handles are declared to be global. Both the init<\/kbd> and myStop<\/kbd> functions need access to this information, but the main function myGUI doesn't know about them. However, declaring them global<\/kbd> (persistent<\/kbd> would have the same effect here since there's only one file) is what's causing the first and second instances to both point to the line<\/kbd> and uicontrol<\/kbd> handles in the second figure, causing incorrect interactions.\r\n<\/p>\r\nHow can you stop that from happening? Two ways:\r\n\r\n- \r\nInstead of declaring the shared variables global, simply initialize them. Replace:\r\n
\r\nglobal hLines hColor\r\n<\/pre>\r\nwith \r\n\r\nhLines = []; hColor = [];\r\n<\/pre>\r\n<\/li>\r\n
- \r\nHere's a solution that is perhaps even more elegant. Since init<\/kbd> only gets called once, don't make it a nested function and instead include the code directly in myGUI<\/kbd>. Since that code runs when myGUI<\/kbd> is created, the variables in question are automatically initialized to their correct values and are now visible to the changeColor<\/kbd> nested function. The code is now slightly shorter, possibly even more readable, and doesn't have unpleasant side effects.\r\n<\/li>\r\n<\/ol>\r\n\r\n
\r\nfunction myGUIclean\r\n \r\n% initialize GUI\r\nhfig = figure('name','Changing line colors');\r\nhax = axes('parent',hfig);\r\nhLines = plot(hax,magic(3));\r\nhColor = uicontrol('style','pushbutton','units','normalized',...\r\n 'position',[0.01 0.01 0.25 0.05],'string','Change line colors',...\r\n 'callback',@changeColor);\r\n \r\n% callback for pushbutton\r\n function changeColor(varargin)\r\n colors = {rand(1,3); rand(1,3); rand(1,3)};\r\n set(hLines, {'Color'}, colors);\r\n end\r\nend\r\n<\/pre>\r\n\r\n\r\nFor a more complex GUI example, see The MathWorks News & Notes - January 2006 article<\/a> and find the code on the MATLAB File Exchange.\r\n<\/p>","protected":false},"excerpt":{"rendered":"\r\nRecently on two different occasions, people have asked me to help debug their nested function< code. I was struck by the similarity of their problems and today will show you the problem and some... read more >><\/a><\/p>","protected":false},"author":39,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[3,6],"tags":[],"_links":{"self":[{"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/posts\/21"}],"collection":[{"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/users\/39"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/comments?post=21"}],"version-history":[{"count":1,"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/posts\/21\/revisions"}],"predecessor-version":[{"id":1790,"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/posts\/21\/revisions\/1790"}],"wp:attachment":[{"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/media?parent=21"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/categories?post=21"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/loren\/wp-json\/wp\/v2\/tags?post=21"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}