Using Matlab App Designer, error using drop down list. Incompatible array sizes.

Question

Aaron 2023-7-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1996998-using-matlab-app-designer-error-using-drop-down-list-incompatible-array-sizes

评论： Voss 2023-7-17

Im atttempting to use a drop down list to select a country, which will pull information from a website and populate an Edit Field(text). The code works for the first two countries, when I use the third I get an incompatible array size error.

 data = webread('https://restcountries.com/v3.1/all');
        
data = webread('https://restcountries.com/v3.1/all');
app.Country_Select.Value = 'Niger';
   if app.Country_Select.Value == 'Jordan'
                 
               app.SpokenLanguageEditField.Value = data{1,1}.languages;
           
   elseif app.Country_Select.Value == 'Brazil'
                
               app.SpokenLanguageEditField.Value = data{2,1}.languages;
            
   else app.Country_Select.Value == 'Niger'
                 
               app.SpokenLanguageEditField.Value = data{9,1}.languages;
   end
Arrays have incompatible sizes for this operation.
   
   app.SpokenLanguageEditField.Value
            

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Answer 1

Voss 2023-7-17

2
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1996998-using-matlab-app-designer-error-using-drop-down-list-incompatible-array-sizes#answer_1274393

在 MATLAB Online 中打开

Instead of using == to compare character vectors, use strcmp.

val = app.Country_Select.Value;
if strcmp(val,'Jordan')
    idx = 1;
elseif strcmp(val,'Brazil')
    idx = 2;
else
    idx = 9;
end
app.SpokenLanguageEditField.Value = data{idx,1}.languages;

== compares element-by-element, i.e., character-by-character in this case since you're comparing character vectors, so the number of elements must be the same, i.e., the character vectors must be the same length. If the character vectors are not the same length, as in 'Niger' == 'Jordan', you'll get the error you got.

You could also use switch/case.

val = app.Country_Select.Value;
switch val
    case 'Jordan'
        idx = 1;
    case 'Brazil'
        idx = 2;
    otherwise
        idx = 9;
end
app.SpokenLanguageEditField.Value = data{idx,1}.languages;