[TwinColSelect] Add buttons for 'Add All' and 'Clear All'

[vaadin-bot]

Originally by spungin

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In the margin between the twin list boxes, there is plenty of room for the buttons '>> and <<' to add or remove all items. This will not take up additional real estate, and is standard behavior for this type of widget.

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Imported from https://dev.vaadin.com/ issue #17768

[vaadin-bot]

Originally by EduFrazao

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Attachment added: screen1.png (15.1 KiB) https://trac-attachments.vaadin.com/trac/17768/screen1.png Screenshot

[vaadin-bot]

Originally by EduFrazao

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Attachment added: TwinColSelect2Widget.java (6.3 KiB) Client side code.

[vaadin-bot]

Originally by EduFrazao

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I agree. I've extended TwinColSelect with this feature, but because its not designed for extension, theres some ugly copy/paste code. Anyway i've attached the client changes.

It will be nice if this features become part of the core component. OBS: This features fits well on the simple ListSelect component too.

[stale[bot]]

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