Try catch error function not working

I am having a hard time using the try catch error function to catch any negative input value for base (b) and height(h). I want to only take in positive value as input and takes the absolute value of the input if it's negative and an error message is displayed. Please help

 if app.ShapeDropDown.Value == "Rectangle"
                % taking in the dimensions of base and height
                
                % Catching resulting errors if the input values are invalid
                try
                b = app.Dimension1EditField.Value;
                h = app.Dimension2EditField.Value;
                catch ME
                if b < 0 | h <0
                   msgID = 'MATLAb:InvalidInput';
                    msg = 'Input for dimension(s) must be positive';
                    baseException = MException(msgID,msg);
                    baseException = addCause(baseException, causeExption);
                    
                    b = abs(b);
                    h = abs(h);
                end
                % Calculate MOI
                Ix = (b*(h^3))/12;
                Iy = ((b^3)*h)/12;
                
                % Displau the MOI on the table
                d = {'Base',b, RegUnit;'Height',h,RegUnit;'Ix',Ix, CalcUnit;'Iy',Iy, CalcUnit'};
                fig = uifigure('Position',[100 100 752 250]);
                uit = uitable('Parent',fig,'Position',[25 50 700 200]);
                uit.Data = d;
                
                % Create axes for the figure. Axes of figure changes
                % depending on base and height entered
                app.UIAxes.XLim = [-1 b+1.00];
                app.UIAxes.YLim = [-1 h+1.00];
                
                %Polar axes
                XX = linspace(b/2, Ix, 500);
                YY = linspace(h/2, Iy, 500);
                
                % % Create a vector that would span the X & Y direction
                % positioned at the center of base and height
                IXline = ones(1,500)*h/2;
                IYline = ones(1,500)*b/2;
                
                % Graph the rectangular shape on the axes
                rectangle(app.UIAxes,'Position',[0 0 b h])
                hold(app.UIAxes);%hold on
                % plot the polar axes
                plot(app.UIAxes,XX,IXline, 'r')
                plot(app.UIAxes,IYline, YY, 'k')
                
                hold(app.UIAxes,'off')
            end
            

Answer 1

[Cris LaPierre]

Your code must generate an error in the 'try' portion before it will execute what is in the catch. I don't see any reason why the current 'try' code should ever generate an error. Therefore, the code in 'catch' never runs.

Try looking at some of the examples in the try-catch documentation page.

[Walter Roberson]

That try/catch can produce an exception -- if app.Dimension1EditField.Value or app.Dimension2EditField.Value do not exist.

However, to have the catch invoked under the circumstance if b < 0 | h <0 then you would need to insert into the try section code such as

if b < 0 | h <0
   error("values out of range");        
end

and remove the "if" from the catch.

... But if you were going to do that, there would not be much point in doing so when you could simply put the if into the main code without any try/catch.