The vertical resizing behavior should not be hard for implementing. Basically, you can set the top margin of the "MainGrid" in order to resize the item from its top border and the RestoredHeight for the bottom border. However, keep in mind that the resizing functionality itself is not very straightforward task and its implementation will require some of your time.
About the vanishing item. This happens because there is no check if the item's size and margin are 0 or lower. In order to resolve this you will need to check for this condition when the resize is in progress.
size of the item makes him vanish (
0 or lower))
// do nothing
I hope this helps.
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