App Designer: Using app.Component.Value vs. event.Value in callback function

Question

Delaney 2022-9-9

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1802225-app-designer-using-app-component-value-vs-event-value-in-callback-function

回答： Walter Roberson 2022-9-9

I am writing a callback function in App Designer where the user has selected an option from a drop-down menu. It seems to me that there are two ways to obtain the value that the user has selected.

Let us say that I have a callback function

function DropDownValueChanged(app, event)

that refers to my UI component DropDown. It seems to me that there are two ways to get the value that was selected from the drop-down menu. According to the section "Callback Input Argments" of this help page, the options are:

value = event.Value;

or

value = app.DropDown.Value;

Is there any tradeoff between using these two approaches? Why even pass event as an argument to the callback function if the same data is stored in app.Component?

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Answer 1

Walter Roberson 2022-9-9

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1802225-app-designer-using-app-component-value-vs-event-value-in-callback-function#answer_1050455

You can code the exact same callback for multiple components. You would not know immediately which component the event was for. It might not even have a particular name: it might be part of an array of objects. Using the event information gets you what you need immediately.