How to avoid ImageSprite cannibalism

Update 2015/12/07: The extra ImageSprite is not needed. Just assign an empty text block to CurrentISP instead of using PlaceholderISP in the TouchUp blocks 

YouTube video: App Inventor - avoiding sprite cannibalism

When more than one ImageSprite can be dragged on a Canvas, unless precautions are taken beforehand they may get 'stuck' together.

This is referred to as ImageSprite cannibalism.

This App Inventor project demonstrates a simple method to prevent this from happening using an ice hockey rink example.

A global variable, an extra ImageSprite and a couple of if blocks enable only one of two ImageSprites to be dragged at a time:

ImageSpriteCannibalism.aia

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