How to get handle from currently running app made in App Designer?

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dzida 2018-6-2

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编辑： Adam Danz 2023-2-12

How to get handle from currently running app made in App Designer? I would like to use it in a matlab function.

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Rodney Case 2020-9-11

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Matlab Apps run in Figure windows. By default, an app's figure window has a hidden handle and is a child of fig(0).

To find the figure window that contains your app, you can use:

h_fig = findall(0,'Name','<App_Title>');  % Where <App_Title> is the string displayed at the top of the app window.

If you design your app to set the Tag of its figure window upon initialization, you could then find it with:

h_fig = findall(0,'Tag','Your_Tag');

The instance of your app is contained in the RunningAppInstance property of the figure window. You can access it as:

h_app = h_fig.RunningAppInstance;

The properties of h_app will include app level globals you've defined plus all of the controls.

Walter Roberson 2020-9-11

Thanks, Rodney.

One implication would be that you cannot have a single figure that is running two different Apps. Not sure why you would want to though ;-)

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Answer 1

Adam Danz 2020-9-11

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编辑：Adam Danz 2023-2-12

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3 ways to access an existing app

In these examples the app's name is "MyApp".

1. Store the app handle when opening the app.

This is the best approach.

app = MyApp;

For more info & demos on this method

2. Find the handle to an existing app figure

The HandleVisibility of UIFigures is set to off by default which makes it a bit difficult to find a UIFigure handle. The code below finds all figure handles and then isolates the figure belonging to your App.

This assumes you only have 1 figure opened with your App's name. For extra precaution, add a Tag to your App and include the tag in the search.

For instructions on how to name your app, see this more detailed answer.

% get handles to *all* figures
allfigs = findall(0,'Type', 'figure'); 
% isolate the app's handle based on the App's name.
app2Handle = findall(allfigs, 'Name', 'MyApp');  % MyApp is the App's fig name
% To include a tag, 
app2Handle = findall(allfigs, 'Name', 'MyApp', 'Tag', 'MyUniqueTagName');

3. Make your app figure handle visible so it can be found with gcf()

Starting in r2020a, open your app in AppDesigner and set your figure's HandleVisibility to 'on' or 'callback'. This can either be done in the App's startup function using MyApp.UIFigure.HandleVisibility='on'; or it can be done in the Design View by selecting your figure handle from the component browser, then set HandleVisibility under the Parent/Child submenu to "on".

Be aware that your App's figure handle will now be available for any plotting function that's looking for the current figure which may lead to undesirable results.

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Adam Danz 2023-2-2

编辑：Adam Danz 2023-2-2

@Raph you're not wrong and perhaps I should clean up some of the words used in my 2020 answer. The question in this thread asks how to get the handle of a running app, not about calling public function from outside of the app. To access an app's public functions, you could use option 1 in my answer.

h = myapp;

h.MyPublicFuncion()

When an app is instantiated, an object is created with its class defined by the app file name when saved in AppDesigner. The class in the example above would be myapp. The app object contains properties such as the app's figure handle but since the app is not a graphics object, functions like findobj or findall can't find it.

Returning the handle to the app is the best option (option 1 in my answer) but if, for whatever reason, that's not possible or preferred, the next best documented option is finding the figure handle to the app. Why? Because 1) since it's a graphics objects, we can find it and 2) app components are children or descendants of the app figure which grants you access to app components if you have the figure handle. This does not grant access to public functions in the app, as you have noted.

Walter Roberson 2023-2-2

"app components are children or descendants of the app figure"

However, general app properties are not children or descendants of the app figure. If, for example, you had created a property directory that you store the path of some file into, then finding the handle of the uifigure will not generally help you get access to that directory property of the app. (It is true that getting the handle of the uifigure might help you grab the handle of a callback attached to some child of the uifigure, and that might potentially help you get access perhaps)

Raph 2023-2-7

编辑：Raph 2023-2-7

@Adam Danz The main reason someone would want the app handle is to run public functions or get public variables. Simply returning the parent figure handle will not allow that. Obviously, its not the 100% case but its the typical use case for this question , imo.

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Answer 2

Wadaane Mohamed 2018-11-25

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I solved it !!!

ok, so first declare a global variable in command window :

global myapp

initiate your app, still in command window :

myapp = MyApp;

there's your handle !!

To use it in your script , first mention that you want to access a global variable, then call your functions:

global myapp
myapp.myfunction('Hello World !')

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Adam Danz 2020-4-7

编辑：Adam Danz 2020-4-27

I wouldn't recommend this approach. There's rarely (never?) a need to work with global variables and they open up a can of worms.

See this answer

https://www.mathworks.com/matlabcentral/answers/462282-creating-apps-communicate-each-other-with-app-designer

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Answer 3

Raph 2023-2-7

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In appdesigner, simply set the top most UIfigure (not the app) Name in IDENTIFIERS to something not too complex such as 'Login' .

% to find the app object
allfigs = findall(0,'Type', 'figure');
app2Handle = findall(allfigs, 'Name', 'Login');
if numel(app2Handle)>0
    app_object = app2Handle(1).RunningAppInstance
    % app object is the app handle, you can call public functions or public
    % variables from it
end