Multiple dropdown inputs to narrow down file options in App Designer

Question

Margaux 2023-7-27

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https://ww2.mathworks.cn/matlabcentral/answers/2001507-multiple-dropdown-inputs-to-narrow-down-file-options-in-app-designer

评论： Jon 2023-7-27

Good morning!

I have been using MATLAB App Designer for two months or so and right now, I am having some troubles using drop downs.

My goal is to have the user choosing 3 different values in 3 different drop downs. By choosing the first value in the first drop down, depending on the available options in the database, the values will adapt in the second drop down and then the user will pick a second value. After the first two values are chosen, the values in the third drop down will adjust again so that the user can choose the value needed. Once the three values are chosen, a different drop down menu otside of this panel will display the files that matches the values chosen by the user so that its data can be uploaded and the data plotted.

Would it be something possible?

Thank you!

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Voss 2023-7-27

Yes, it is possible.

Here is a similar question that may be useful:

https://www.mathworks.com/matlabcentral/answers/1999063-creating-2-dynamic-and-dependent-dropdown-menus-in-app-designer

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Answer 1

Jon 2023-7-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2001507-multiple-dropdown-inputs-to-narrow-down-file-options-in-app-designer#answer_1279762

编辑：Jon 2023-7-27

在 MATLAB Online 中打开

dropdownquest.mlapp

I have attached a very simple example of how you might have the choice from one drop down menu change the possible choices from a second drop down. In this example initially both drop downs have three items. The first has Choice A, Choice B, Choice C, the second has Choice 1, Choice 2, Choice 3. When you select an item from the first list, the corresponding element is eliminated from the second list. So if you pick Choice B from the first list, the second drop down becomes Choice 1, Choice 3 (Choice 2 is eliminated). Anyhow this is just to illustrate the principle. You can modify with your specific logic.

The key idea is to use the value changed callback from the first drop down, to modify the Items property of the second,

        % Code that executes after component creation
        function startupFcn(app)
            % Define initial drop down item lists
            app.DropDown1.Items = {'Choice A','Choice B','Choice C'};
            app.DropDown2.Items = {'Choice 1','Choice 2','Choice 3'};
        end
        % Value changed function: DropDown1
        function DropDown1ValueChanged(app, event)
            value = app.DropDown1.Value;
            % Modify second drop down menu according to choice made here,
            % specifically eliminate corresponding drop down item in the
            % second list
            idx = find(ismember(app.DropDown1.Items,value)); 
            app.DropDown2.Items(idx) = []; 
        end