[1eyedjack]

I have been experimenting with the process of changing your mind about a card to be played, in mid play of the card but before release.
I consider that this needs improvement.

Once you tap on a (legal) card to be played (at your turn to play), then the card is usually released (played to the table) when you "let go" of the card (release the "tap").
Dragging and releasing the card also serves to play the card.

Now, suppose you develop the (bad) habit of placing your finger on the card that you expect to play, but have not committed to playing, and then change your mind before releasing the card. Then you change your mind about playing that card, in favour of another, while your figure is still holding on to the card. Akin, if you wish, to a declarer in a face to face game extracting a card from his hand and then replacing it in his hand without exposing it.

OK, not a good habit to develop in a player. Maybe the software should discourage it. In real life a "touched card" in dummy is often regarded as a played card (in rubber at least).
But on the other hand, in a sense "no foul", since the other players at the table cannot see you dragging your card all over the screen and then replacing it in your hand.

The software DOES allow you in these circumstances to replace your card in the original position without exposing it and then select another card. It requires you to drag the card away from its original position and then replace it in its original location before release. But it is EXTEMELY sensitive to the location of drop-off. Vary the location by just a millimeter or so and it will play that card.

If anything, if by design there is an intent to allow the "change your mind before committing to play" option, then by default it should be geared to be less sensitive. After all, if in error it replaces the card in your hand in error when you actually intended to play it, then you can still repeat the process without damage, whereas if you play the card but did not intend to, then the undo-after-play facility has more problems associated with it.

Arguing in favour of high sensitivity (as currently programmed) I have to agree that the vast majority of the time, when you touch a card you do genuinely wish to play that card. Even if you entertained doubts there is a low frequency that you would change you mind after reconsidering. So you might not want to build into it a high frequency of unintentionally replacing cards in the hand.

A completely different approach to the problem would be to deny physical dragging of cards in the mobile interface. Thus if you finger a card and then attempt to drag it, the card would main stationary but your finger would slide off the card which would remain unplayed. In order to play the card you would have to tap and release while your finger remained in contact with the card. This is the way that the bidding works: If you tap on a bid but drag your finger away because you changed your mind, it cancels the proposed bid before it is made. That works well, to my mind, and this principle could be extended to the card play.