Why this would be helpful

Currently, you can only select one sprite, one costume, and one sounds. Being able to select multiple of these will provide the following benefits:

• Allows batch operations
  • Duplicate multiple sprites or assets (costumes/sounds)
  • Delete multiple sprites or assets without having to aim for the delete button for each one
    • Rather than individually clicking on each item you want to delete, you just: hold shift, select the range you want to delete, right click, and delete
  • Batch export multiple assets quickly (I suppose this is useful for animators?)
• Create folders easier with the folders addon
  • Instead of making the folder first then moving sprites in individually, you can either:
    1. Multi-select the sprites you want to add to the folder, right click, and add to folder
    2. Create new folder, multi-select sprites you want to add to folder, and drag in
• Add sprites or assets into backpack easier

Additional features up for debate (these probably fit as their own separate addons)

• Multi-select projects for deleting (or sharing using the share-through-mystuff addon) in the My Stuff page
  • This was rejected in the SA community discord as being too API spammy, but perhaps this idea should be revisited since manually deleting/sharing individual projects will take up the same number of API calls anyways.
• Multi-select assets in the Scratch library. Mockup from here
  

How this addon works

Three selection operations, the first of which is already implemented in vanilla Scratch:

• single click clears your previous selection and selects the item you just clicked on (like normal)
• CTRL + click adds the item to your selection
• SHIFT + click adds all items between last selection and the new click to your selection

There may need to be discussion about deselection operations.

If the user has selected more than 1 sprite/asset, they enter "Multi-select Mode" There are two considerations that this helps solve:

1. In Scratch, selecting a sprite/costume/sound opens it into the code area/costume editor/sound editor. This can be laggy at times, if the sprite's code or the asset is complicated or the user is using a potatoboard as a device. This may interfere with the user whenever they are trying to multi-select. Therefore, whenever the user enters "Multi-select Mode" (as in, they have selected multiple assets), Scratch doesn't open the latest-selected item
   • TL;DR: the opened sprite/asset remains as the first item the user selected
2. Make it clear to the user that they have selected multiple items. This prevents the user from accidentally deleting an item they didn't mean to because they accidentally multi-selected it but it ended up offscreen whenever they scrolled or something. Some possible solutions to this:
   • Add a checkbox selection system that shows up only when the user multi-selects something
   • Gray out the code area/costume editor/sound editor to indicate they have selected multiple items (not preferable)
   • Add an obvious GUI element that states "You have selected ${x} sprites/costumes/sounds"

Possible alternatives

Delete other assets

• "Delete others" button on costumes and sounds context menu #4692
• New addon: "delete other assets" (delete-others) #7030

Additional context

Resolves discussion #5183

Suggested in the SA community Discord:

• Multi-select sprite selector
• Multi-select costumes/backdrops
• Delete costume improvements
• Multi-select projects in My Stuff page (was rejected as API spammy, but perhaps this should be discussed further)