How to link uialert to my App Designer UI figure?

I recently took over a MATLAB project of a former colleague and is still learning how to write MATLAB code correctly. I would like to change working code that currently uses msgbox to now rather make use of uialert(). I can however not find a way to link the UIFigure of my app to the uialert function. My understanding is that the arguments should be as follows: uialert(uifigure,message,title). My problem seems to be with the uifigure argument.

The uialert Help indicates that the uifigure must be created with the uifigure function. When I use the following code I do get a new uifigure and the alert message appears in front of it as expected.

f = uifigure;
uialert(f,'Test','warning');

I do however want the alert message to appear in front of the App Designer UIFigure rather than a newly created figure. I found code here on the forum that identifies the name of my App Designer figure:

hFigs = findall(groot, 'Type', 'figure')

hFigs = Figure (VTT) with properties:

Number: []

Name: 'VTT'

I tried several ways to try to refer to the name of my App Designer figure but none of them worked. Below are two examples of what I tried.

uialert('VTT','Test','warning');
uialert(hFigs.Name,'Test','warning');

I got the following error with both lines of code:

Error using uialert (line 35)

Invalid or deleted figure handle. First argument must be a valid figure handle

I might be using the wrong terminology but I can not find any answers in this forum that explained to me how I can link uialert() to appear in front of the the App Designer UIFigure.

[Adam]

Did you not keep hold of the class object you run for your app designer code? e.g.

myApp = MyAppDesignerProject( );

If you do then its figure should just be

myApp.UIFigure

It's always far better to just keep hold of handles to objects when you create them than try to fish them out with a huge findall net on the root node afterwards!

[Hannes Truter]

No. I do not see anything like that.

In the App Designer Code View window I see the following code that looks like it was generated by App Designer.

In the Component Browser area of App Designer I see

Thank you very much for your help. Your answer solved my problem for the most part.

I typed the following into the command window and it worked. The alert message appeared in front of the app UIFigure

myApp = app2( );
uialert(myApp.VTTUIFigure,{'New'},'File name error','Icon','warning','CloseFcn','uiresume(gcbf)');

Most of the second line's code comes from an answer to a different question in this forum.

https://uk.mathworks.com/matlabcentral/answers/463287-using-uialert-with-uiwait-and-uiresume

Now I just need to find the correct place to add the first line of code above to capture the class object.

[Adam]

Yes, it is possible (and usually desirable) to change the default UIFigure name in the app so that would be the equivalent.

The first line should just be whenever your app is launched, which it must have been in order for you to be attaching a uialert to it.

[Hannes Truter]

When I add the line "myApp = app2( );" to the code of my my app it opens a second instance of the UIFigure instead of linking to the existing figure of the app. I do not know if I'm adding it in the wrong place in the AppDesigner code. I could not find the App Designer code that creates the UIFigure. I therefore created a StartupFcn Callback as described on the MathWorks site:

https://uk.mathworks.com/help/matlab/creating_guis/app-designer-startup-function.html

I have also placed the "myApp = app2( );" code in other functions but get the same result of a second UIFigure opening.

I can not see a way of placing the "myApp = app2( );" code inside the Add Designer code without renaming the .mlapp file to .m and editing it, as described in the following link.

https://uk.mathworks.com/matlabcentral/answers/401234-app-designer-how-to-run-code-before-components-are-created

There must surely be an easier way to implement the uialert function.

In the App Designer created code I see several instances that refers to app.VTTUIFigure

 % App initialization and construction
    methods (Access = private)

        % Create UIFigure and components
        function createComponents(app)
 
            % Create VTTUIFigure
            app.VTTUIFigure = uifigure;
            app.VTTUIFigure.SizeChangedFcn = createCallbackFcn(app, @VTTUIFigureSizeChanged, true);

The code above shows that app.VTTUIFigure is created by means of uifigure. This fulfills the requirement indicated on the uialert help page. When I try to use this app.VTTUIFigure figure reference in uialert it generates the error message indicated below.

uialert(app.VTTUIFigure,{'New'},'File name error','Icon','warning','CloseFcn','uiresume(gcbf)');
%Error Message: Undefined variable "app" or class "app.VTTUIFigure".

[Adam]

Don't put that inside your appdesigner code. You are massively over-complicating things. I guess I didn't explain it clearly enough.

myapp = app2( )

is the code that will launch app2 (assuming that is what your app designer file is called - note this is the file/class name, not whatever name is given to the uifigure inside this). That is why you get a 2nd one when you call it again.

You must already be doing that somewhere, it's likely though that you simply don't store the output argument and just call

app2

instead. Literally all you need for this is to find where you already launch the UI and keep hold of that return argument. Then you can use it later on to access its uifigure (or anything else in it that you wish).

[Hannes Truter]

I must be doing something fundemantally wrong so I'll try to explian what I do to test my code.

There is a button on the app figure that activates a callback to the function that I'm editing. I use the MATLAB editor to edit the code of my function that calls the uialert function. I test my code by clicking the Run button in the App Designer window. I do not call my app from anywhere. The App Designer starts the app. I do not know of a way to add your code in App Designer to start the app with your code.

My latest debuging efforts:

I called the app (app2) from the command window by typing in myApp = app2( );

This did open the app. When I then clicked on the button on the app figure the code ran up to the breakpoint that I set at the point where I call uialert. When I stepped past the uialert code below, I got an error: Undefined variable "myApp" or class "myApp.VTTUIFigure".

uialert(myApp.VTTUIFigure,{'New'},'File name error','Icon','warning');

When I type both lines below in the command window without clicking on the button on the app figure, the alert window does open in front of the app figure.

myApp = app2( );
uialert(myApp.VTTUIFigure,{'New'},'File name error','Icon','warning');

The same uialert code works in the command window but not in my callback function code.

By stepping through all the code I found the place in the App Designer code where the figure is created.

This is inside the App Designer app2.mlapp code which I can not edit.

[Adam]

Ah, if you are running your uialert from a button within the app then you have access to the app within that button's callback, as you do in all callbacks. So

app.VTTUIFigure

should be the uifigure, in your callback. You don't need to add in the code I mentioned to keep the app handle in that case. I assumed, from what you were saying, that you were trying to call uialert externally to your app and give it the figure of your app as an argument.

[Hannes Truter]

When I use app.VTTUIFigure in

uialert(app.VTTUIFigure,{'New'},'File name error','Icon','warning');

I still get the same error message: Undefined variable "app" or class "app.VTTUIFigure".

I used code from this MATLAB answer to track the status of VTTUIFigure. I wanted to see if I can find the point where VTTUIFigure can not be called any more.

I executed the code below next to K>>, from the command window, at different times while I stepped through the APP Designer code of the app.

K>> class(app.VTTUIFigure)
K>> isuifigure(app.VTTUIFigure)

Below is the function that is called from isuifigure() above

function val = isuifigure(h)
val = ~isempty(matlab.ui.internal.dialog.DialogHelper.getFigureID(h));
end

The APP Designer code that creates the VTTUIFigure starts executing when I step into the "runningApp" part of the code (copied below) which is inside the AppManagementService.m module.

try
    runningApp = evalin('base', sprintf('%s(%s);', appName, appArguments))
catch exception

Just after the VTTUIFigure of the app was created I ran the code to check its status. Below is the code I executed in the command window as well as the responses:

K>> class(app.VTTUIFigure)
ans = 'matlab.ui.Figure'
K>> isuifigure(app.VTTUIFigure)
ans =  logical 1

I executed the above code every time after stepping to the next line in the App Designer code.

Every time when the code returned from the function below to the "runningApp" code above that called the AppDesigner code, the VTTUIFigure status started giving me error messages.

% Construct app
function app = app2
    % Create and configure components
    createComponents(app)
    % Register the app with App Designer
    registerApp(app, app.VTTUIFigure)Just after the 
    if nargout == 0
        clear app
    end
end    %Error status happens after stepping back from this end to runningApp = evalin('base',

Just after exit of above code, the VTTUIFigure class changes

K>> class(app.VTTUIFigure)
Undefined variable "app" or class "app.VTTUIFigure".

K>> isuifigure(app.VTTUIFigure)
Undefined variable "app" or class "app.VTTUIFigure".

When I execute the uialert() code below immediately after VTTUIFigure is created in the AppDesigner code, it creates the expected alert window and message in front of VTTUIFigure.

uialert(app.VTTUIFigure,{'New'},'File name error','Icon','warning');

I tested this by setting a breakpoint just after the AppDesigner code below, and then executing the uialert code from the command window.

% Create VTTUIFigure
            app.VTTUIFigure = uifigure;
            app.VTTUIFigure.Color = [0.9294 0.6902 0.1294];
            app.VTTUIFigure.Colormap = [0.2431 84 0.3451 0......9765 0.9843 0.0824];
            app.VTTUIFigure.Position = [100 100 507 482];
            app.VTTUIFigure.Name = 'VTT';
            app.VTTUIFigure.Resize = 'off';
            app.VTTUIFigure.SizeChangedFcn = createCallbackFcn(app, @VTTUIFigureSizeChanged, true);

[Adam]

As long as you are in a callback of your application 'app' should never not exist (assuminig the argument is called 'app'. From my experience there is no way of changing the name of this argument so I assume it is). And if the app exists then so should its uifigure property which you named VTTUIFigure.

You shouldn't have to be messing around with any code that constructs the app or creates the figure.

[Hannes Truter]

Everything you wrote above seems logical but the reality does not seem to match it in my app. I can not spend any more time on this. I'll just make peace with the fact that uialert can not work with the GUI of my app. I can not find a single example on any of the forums I looked at where anybody successfully implemented uialert with their uifigure. I'll just keep on using the message box.

Answer 1

[Eduardo Gil]

I am having the same problem. My code is very straightforward - just an error message to the user in case "end date" is less than "start date".

% error message in case end_date <= start_date

d=app.UIAxes;

if end_date <= start_date

uialert(d,'Plot End Date must be greater than Plot Start Date!','Invalid Input');

end

I get the following error:

Error using uialert (line 42)

Invalid or deleted figure handle. First argument must be a valid figure handle

Error in Weather_Chart/refreshplot (line 214)

plot_data(app,xdata,ydata,zdata,zdata_backcast,min_date,max_date);

Error in Weather_Chart/DatePicker_2ValueChanged (line 266)

refreshplot(app)

Answer 2

[Eduardo Gil]

Found the aswer. It's not app.UIAxes, but rather the name for the entire figure (in my case: Load_Analysis matlab.ui.Figure). A bit of trial and error:

uialert(App.Load_Analysis,'Plot End Date must be greater than Plot Start Date!','Invalid Input');

[Hannes Truter]

Thank you for providing the solution you found for your problem.

Are you using uialert with a secondary figure you created with your app code or are you using it with the main app figure created on the "Design View" tab in App Designer?

My problem is specifically on how to use uialert with the main figure created in App Designer. I only have the one figure. I do not create any secondary figures in the app code. It looks to me like there is fixed code in the % Create UIFigure section of the App Designer startup code that disables the uialert functionality with the main app figure.

[Frederick Breidt]

Greetings,

I found it, try: app.UIFigure