MATLAB Answers


Java slider not Responding

Asked by Lawson Hoover on 12 Dec 2012

The slider is saved as S.sl1 and I convert it to sl1 and output it. I then convert it to a java slider in another function with :

   jScrollBar = findjobj(sl1);
   jScrollBar.AdjustmentValueChangedCallback = @updateplot;

Then the call back function is:

function updateplot(sl1,ht,funcNum)
x = get(sl1,'Value');
Beam.Location = x;
switch funcNum
    case funcNum == 1
        y = Cantilieverd_Point(Beam);
      case funcNum == 2
          y = Simple_Point(Beam);


Where ht is the plot that is being updated and the ' y = ' is another function which creates the y value. When I run this it does not return an error, but it also does absolutely nothing to the graph. I want it to continuously update the graph based off of the slider value.


How does updateplot know the value of funcNum? ht is an EventData object - it has no 'ydata' property. Is this a slider or a scrollBar.

The callback can not be being called - or you would see errors.

A more complete code example is needed to be more helpful.

@ Matt Fig, well the Listener did work in a way. It would update once and then not run again. To tell you the truth I might just move on past this and come back to it later. I am still very new to MATLAB and still trying to get a hold of the concepts.

@Lawson That is a vital bit of info. The callback is evaluated once, throws an exception and gets removed by MATLAB. You need something like:

jScrollBar.AdjustmentValueChangedCallback = {@updateplot, ht, funcNum};

The callback should then be declared as:

function updateplot(sl1,EvenData, ht, funcNum)

sl1 and EventData are added automatically to the inputs by MATLAB>


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1 Answer

Answer by Jan Simon
on 12 Dec 2012

There are several problems in your code:

1. Here the callback is defined with no inputs:

jScrollBar.AdjustmentValueChangedCallback = @updateplot;

But in the definition of the callback function, 3 inputs are required.

2. Look at the documentation of switch/case again. The term "funcNum==1" is evaluated to either true or false, but you want to switch for the value 1 or 2. Therefore you need:

switch funcNum
  case 1   % Not "funcNum == 1"

I suggest not to use a Java slider, but the standard Matlab sliders. You cann attach a listener to them also:


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