"Attempt to reference field of non-structure array." when accessing a handle

Question

Thomas 2014-2-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/115175-attempt-to-reference-field-of-non-structure-array-when-accessing-a-handle

回答： Image Analyst 2014-2-7

Ive written a GUI code which plots real time data from sensors With my GUI, i have a popup menu which lets the user select a value. In the function handle i store the chosen data into a handle "handles.numberofsensors".

The real time plotting is done by a timer function. I am able to access "handles.numberofsensors" from a push button callback function but I cant access "handles.numberofsensors" from the timerFcn of the timer object without the error.

Below are some excerpts from my code:

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      function popupmenu_Callback(hObject, eventdata, handles)
      contents = cellstr(get(hObject,'String')); 
      handles.numberofsensors = contents{get(hObject,'Value')};
  % stores popupmenu value into the handle
      fprintf('Number of sensors to be use: %s\n', handles.numberofsensors);
      guidata(hObject, handles);  %update handles
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
      function start_button_Callback(hObject, eventdata, handles)
      filename = 'C:\Program Files\xxxxxxxxxxxxxxxx';
      d = get(handles.timer, 'UserData');      
      d.data = []; % array for the data to plot
      d.data2 = [];
      d.data3 = [];
      % Figure/axis properties
      axes(handles.axes1);
      d.line_handle(1) = plot(NaN,NaN);
      d.line_handle(2) = copyobj(d.line_handle(1),gca);
      d.fid = fopen(filename, 'r');    
      set(handles.timer, 'UserData', d);
      % Only START TIMER if it is not running
      if strcmp(get(handles.timer, 'Running'), 'off')
          start(handles.timer);
      end
      %ABLE TO ACCESS HANDLE HERE WITHOUT ERRORS
      switch handles.numberofsensors
          case '2'
              fprintf('Producing real time plot for 2 sensors.\n');
          case '4'
              fprintf('Producing real time plot for 4 sensors.\n');
      end
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  %%%%timerfcn%%%%%
      function updateFigure(hObject, eventdata, handles)
      % Timer timer1 callback, called each time timer iterates.
      % Reads in new data from text file, appends data to correct format
      % and plots/updates the values in the plot.
      d = get(hObject, 'UserData');          
      % read new data from file
      tmp = readFile(hObject);
      % append to array in user data
      d.data = [d.data transpose(tmp{1})];
      d.data2 = [d.data2 transpose(tmp{2})];
      d.data3 = [d.data3 transpose(tmp{3})];
      %Plots data according to how many sensors are chosen
      #ERRORS HERE. im unable to access handles.numberofsensors anywhere in this function
      switch handles.numberofsensors
          case '2'
              set(d.line_handle, 'XData', d.data2, 'YData', d.data);
          case '4'
              set(d.line_handle, 'XData', d.data2, 'YData', d.data);
              set(d.line_handle(2), 'XData', d.data2, 'YData', d.data3, 'color','r');
      end
      set(hObject, 'UserData', d);

Pretty much if i try access 'handles.numnberofsensors' anywhere in the timerFcn above, ill get the "Attempt to reference field of non-structure array." error.