ENH: Improve usability of Directory Button by using native dialog

[jamesobutler]

This aims to improve directory selection by using the native dialog instead of Qt's own widget-based dialog design.

See 3D Slicer forum discussion of how users have been doing other methods to avoid using widgets that use Qt's widget-based dialog.
https://discourse.slicer.org/t/using-native-file-dialog-for-selecting-files-and-folders/17926

Qt widget-based dialog	Native dialog (on Windows)

[lassoan]

Thank you for working on this. Native file dialogs are now probably preferred by most users, so I think it is a good idea to use them by default.

Is there a reason why you switched from ctkFileDialog to QFileDialog instead of just using the DontUseNativeDialog flag to choose between native and CTK style? You could even change the default to use native dialog, but keep the door open for using the CTK style dialog to reduce the potential undesired impact of the change.

[jamesobutler]

I switched from ctkFileDialog to QFileDialog because the customizations of ctkFileDialog appeared to be mostly related to modifying the functionality of a Qt widget-based dialog. So switching to the native file dialog is essentially going back to using a QFileDialog without those additional customizations.

We can't just remove the following DontUseNativeDialog specification as there is other code in the class that requires the use of a Qt widget-based dialog with calls such as setBottomWidget.

CTK/Libs/Widgets/ctkFileDialog.cpp

Lines 130 to 135 in 01ab373

	// The findChild<QDialogButtonBox*>() call fails on Mac/Qt5 because native
	// dialogs don't publish any internals. No problems on other OS.
	// Can be applied to Qt4 as well, if problems arise there.
	#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
	this->setOptions(DontUseNativeDialog);
	#endif

[lassoan]

The extra features don't have to be deleted, but they would only be used if dontusenativedialog flag is enabled.

[lassoan]

Thanks for the updates. These small changes are much less likely to cause any regressions in any CTK-based projects. Just need to sort out those few syntax errors.

[jamesobutler]

I've pushed an update based on @finetjul 's suggestions

[jamesobutler]

Thoughts on latest updates @lassoan @finetjul ?

[lassoan]

Thank you!
I had just two comments that should be easy to address.

[lassoan]

Thank you, this looks good to me.

[jcfr]

Suggested change

	if (!(this->UsingNativeDialog))
	if (!this->UsingNativeDialog)

[jamesobutler]

I've pushed commit with change to #977