App Designer returning Value in EditField

I wrote a code to calculate some values I insert in the Edit fields.

First of all do I have a DropDown Menu, with some values which I want to calculate with.

After I performe the calculation (with the value from DropDownMenu and values from EditField) do I want to return the result in an Edit field.

If run the programm and Insert all my values do I get the following error:

"Error using matlab.ui.control.internal.model.AbstractNumericComponent/set.Value (line 111)

'Value' must be a double scalar."

That's my code for the DropDown menu. I want to safe the value in the variable "app.d_th"

        % Value changed function: aDropDown
        function aDropDownValueChanged(app, event)

            app.d_th = app.aDropDown.Value

        end

I have a Calculation Button which looks like this. I have shortened the entire calculation. that's just to show you how it looks. The goal is when I press the Button I want to performe the calculation and display it in the "ResultEditField"

                % Value changed function: BerechnenButton
        function BerechnenButtonValueChanged(app, event)

        value = app.BerechnenButton.Value;
       
d_th = app.d_th/1000 %in meter. 3.6mm = 0.0036m
p_h = app.p_h * 10^5 %Hochdruck in pascal


m_flow =  d_th.^2 + p_h 
app.ResultEditField.Value = m_flow

        end

Any hints?

Answer 1

[Mario Malic]

Hi,

app.aDropDown.Value is one of the values in Items (if ItemsData is empty), therefore it's a character array.

if you set ItemsData as well to be numeric, then Value property will be of the same type. However, you can keep it simple and use line below to fix the issue.

app.d_th = str2num(app.aDropDown.Value)

[Giancarlo Meccariello]

okey, that worked. next error:

"Python Error: TypeError: must be real number, not array.array

Error using matlab.ui.control.internal.controller.ComponentController/executeUserCallback (line 429)

Error while evaluating StateButton PrivateValueChangedFcn."

[Mario Malic]

Do you use Python anywhere in your code?

[Giancarlo Meccariello]

yes I do. I have some functions like this

py.CoolProp.CoolProp.PropsSI('D','T',273.15+ T_gc_out ,'P',p_h,KM)

[Mario Malic]

Hm, you'll have to convert the output of these as variable types are different, even though their values are the same. On this one, you'll have to use the search tool and find related questions.

[Giancarlo Meccariello]

I started again with the programm and checked every step.

I found the problem, the only mistake was the missing conversion str2num!

Everything fine now!

THANK YOU