Two windows pop up when I call uigetdir from appdesigner app

Question

Josh Zagorski 2020-3-4

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评论： Walter Roberson 2020-3-5

When i call uigetdir from appdesigner two windows pop up, as well as lock up sometimes when selecting a DIR. Every time two Windows pop up, but it only locks up sometimes. By locking up, I select the folder I would like (twice), then, I can't do anything in the app or appdesigner windows, but I can still use any other MATLAB windows with no issues.

function FileDirEditFieldValueChanging(app, event)
    fileDir = uigetdir('C:\')
    app.FileDirEditField.Value = fileDir;
 end

When it does work, I also get the following output:

fileDir =
    '%filepath I want%'
fileDir =
    '%filepath I want%'

I would also like it to pop up (with ONE window) when you click on the Edit Field vs. on Value Changing. Should I be using a different element? "Edit Field (Text)" looks like the best option

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Answer 1

Walter Roberson 2020-3-4

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I wonder --

In some cases, "change" callbacks are invoked when you click or type on an edit field, to deal with the fact that you are changing "away" from what the contents used to be. And in some cases, "change" callbacks are also invoked after you set a new value for the field, indicating that the field has "changed".

In most situations that I can think of, setting a value directly by assignment or set() does not invoke a change callback. However, I can think of at least one way of configuring callbacks where callbacks can get invoked after an assignment or set() .

My recommendation would be to have a button to signal that you wanted uigetdir() to be brought up and the result written into the edit field, rather than having an edit callback the way you have. The edit callback should be for validating things the user typed in by hand.

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Walter Roberson 2020-3-4

https://www.mathworks.com/help/matlab/ref/matlab.ui.control.editfield-properties.html says

This callback executes as follows:

As the user types in the edit field, the callback executes repeatedly.
When the user presses Enter, the callback executes.

If the edit field value changes programmatically, then the callback does not execute.

This leads to the possibility that the first callback is due to "user types" and the second is due to "user presses enter" (which I suspect also gets triggered if the user navigates away from the field.)

Anyhow, we can see that if the user were to try to hand-edit the text, that the callback would get invoked repeatedly, once per keystroke. With the way you programmed the callback, that means that every time the user tried to press a key to edit the field by hand, that uigetdir() would pop up. That is not a desirable UI interaction.

Perhaps you could set a "being editted" variable. The ValueChanging callback would examine it, see that it is not set, and would set it and then invoke uigetdir() . The callback would get invoked a second time as you have seen, but the callback would test the flag, see it was set, and gracefully returned. Then you would also create a ValueChanged callback in which you would clear that flag and do any work involved in finalizing the directory selection.

Josh Zagorski 2020-3-4

I clicked into the Text Box and pressed space once and always two windows pops up, I pressed asdf and again two windows pop up.

Walter Roberson 2020-3-5

Is there any documented circumstance under which the Value Changing callback is invoked less than twice? Is your current code prepared for being invoked more than once?

What you are looking for is a variety of "value is starting to change" callback. That does not exist, however.

There just might be a way to work such a callback using event listeners, but I do not know enough about how App Designer works to say whether that could be done or not.

I offered you a work-around: the flag that you reset when the edit is confirmed by the ValueChanged callback.

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