CODEWITHSUNDEEP
matlabeventslistener
S.Maria
S.Maria

Reputation: 131

Implement MATLAB listener which notifies that there is enough data in a matrix

I am trying to implement a listener in my MATLAB DAQ program, which notifies, if enough data are available in my acquired data matrix (and then saves a backup etc).

I know that there is something similar existing in the Data Acquisition Toolbox with the event 'DataAvailable' and NotifyWhenDataAvailableExceeds (frequency, when the event is fired). Unfortunately my device is not supported by the toolbox and I set up a DAQ program by myself by using a timer and querying the instrument values with fprintf and fscanf (Instrument Control Toolbox).

For a first approach to implement this, I read the documentation (i.a. Events and Listeners Syntax) and tried to implement an example, where an empty matrix is expanded by a for loop and a listener is notifying, when there are e.g. 100 data points available. However, I failed completely, because I couldn't figure out, how to implement, how the listener "notifies" this. Is it even possible to create "own" events or can MATLAB only listen to already existing events given in the documentation?

I am not sure if I got the concept right and would be glad if someone would give me a quick overview, if and how it is possible, what I am trying to do.

Below you find a Code example. I am totally aware, that it can't work like this yet, but I hope it makes clear what I am trying to do:

%% Class definition

classdef DAQClass < handle
   properties
  DataMatrix %Does this make sense to put the matrix as property?

                %Maybe better as event data?
   end
   events
      EnoughData
   end
   methods %Does it make sense to put the condition when to notify, in a    method??
    %how can I access it for my listener 
      function IfEnoughDataAvailable(obj,DataMatrix) 
         if (length(DataMatrix)>100)
            notify(obj,'EnoughData');
         end
      end
   end
end


%% Add listener, run code to fill data matrix

DAQObject=DAQClass;
DAQObject.DataMatrix=[];
lh = addlistener(DAQObject,'EnoughData',@reactToEvent);

for k=1:1000
    DAQObject.DataMatrix(k)=k;

end

Upvotes: 1

Views: 114

Answers (1)

Sam Roberts
Sam Roberts

Reputation: 24127

I'd implement it like this, using a property listener rather than a listener (notice that I've put DataMatrix to be SetObservable):

classdef DAQClass < handle
    properties (SetObservable)
        DataMatrix = []
    end
    properties (Access = private)
        DataMatrixListener
    end
    methods
        function obj = DAQClass
            obj.DataMatrixListener =...
                addlistener(obj, 'DataMatrix', 'PostSet', @obj.reactToEvent);
        end
        function reactToEvent(obj, ~, ~)
            if length(obj.DataMatrix)>100
                disp('Enough data available') % Do actual thing here
            end
        end
    end
end

Then you can run:

>> d = DAQClass
d = 
  DAQClass with properties:

    DataMatrix: []
>> for i = 95:105
disp(i)
d.DataMatrix = 1:i;
end
    95
    96
    97
    98
    99
   100
   101
Enough data available
   102
Enough data available
   103
Enough data available
   104
Enough data available
   105
Enough data available

Note that the reactToEvent method does the length-checking itself, and reactToEvent is called whenever DataMatrix changes. So you might want to put some logic in there so that it's only called once, when DataMatrix increases beyond 100, rather than every time it's beyond 100 (e.g. it could process the content of DataMatrix and then reset DataMatrix to [], treating it like a buffer.

Upvotes: 1

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