Get selection index for DropDown object using AppDesigner

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Jim Hokanson 2017-11-10

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评论： Mario Malic 2021-2-19

Using AppDesigner, how do I access the selected index of a DropDown menu. The Value is the selected string but I can't find anywhere that indicates the selected index. Instead I seem to have to do:

I = find(strcmp(h.Items,h.Value));

Is this really the suggested approach?

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Matt J 2017-11-10

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编辑：Matt J 2017-11-10

The h.Value property has different behavior depending on how h.Items and h.ItemsData are set up. If you define the ItemsData property to be some sequence of numeric indices i=1:N, then h.Value will be the numeric value of i corresponding to the selection.

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Mario Malic 2021-2-19

编辑：Mario Malic 2021-2-19

在 MATLAB Online 中打开

TLDR on the bottom.

This behaviour is standard I guess, snippet below is ran in 2020b

a = 'b'
a*2
ans =
   196

Referring to your picture from the component inspector @Erik:

If your expand your Items, they will appear only in one row which means that it has only one element
Can you check if in your ItemsData, each entry is in its own row? If yes, that will cause the data to be treated as cell array of character arrays. Even if it consists only of numeric values, those will be treated as characters

An example, how you'd write things in the App Designer:

   Items = opt1, opt2, opt3
   ItemsData = 1 2 3
   % Items will be 1x1 cell array, whereas items will be 1x3 numeric array
   
   Items = opt1, opt2,
           opt3
            % NOTE <-- Sometimes users like to finish the entry with 'Enter' button so we have an empty row like here
   ItemsData = 1
               2
               3
   % Items and ItemsData will both be 3x1 cell array of character arrays, 3rd Item will be empty
   
   Items = opt1, opt2
   ItemsData = 1, 2, 3
           % same note as above, an empty row       
   % Items will be 1x1 cell array, whereas ItemsData will be 2x1 cell array of character values,
   % Since Items(1) refers to ItemsData(1), ItemsData(1) will appear in Value

On the last case, which you showed on the picture, if I expand the Value box, I see the same, except in 2020b other rows are a shifted by space like this.

   1
    2
    3

TLDR: Check for empty rows in your Items and ItemsData.

To get the access to app in your command window, you can call your app directly

app = NameOfTheApp;

If you have opened the app already and you want to get the access, there's property called RunningAppInstance in App Designer figure. If you have more figures open, then use app tags to differentiate your app from other figures.

app = get(findall(0,'type', 'figure'), 'RunningAppInstance');

Erik 2021-2-19

在 MATLAB Online 中打开

Thanks on the info on how to get access to a running app.

There is no way in my version to enter the ItemData so that it becomes a numerical array. What ever I do in de compent inspector, the end result is the same (see below). And yes the (single) Value is shown in the inspector as numbers under each other while the ItemData is shown as 1,2,3,4

But, like I said, in the 2020b version, this behaviour fortunately changed apparently

>> app.DropDown
ans = 
  DropDown (Option 1) with properties:
              Value: '1 2 3 4'
              Items: {'Option 1'  'Option 2'  'Option 3'  'Option 4'}
          ItemsData: {'1 2 3 4'}
           Editable: 'off'
    ValueChangedFcn: ''
           Position: [131 192 100 22]

Mario Malic 2021-2-19

Oh, I see what you mean now.

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