Limit block creation to one instance?

Lyssa Neel

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Sep 28, 2016, 12:00:21 PM9/28/16

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Hi,

Is there a way to limit a user to creating no more than one instance of a particular block? Like a block element named "maxInstances" that I have totally missed?

Barring that, I thought I might be able to disable the block in the toolbar if it is already on the workspace. Does anyone have other suggestions? Zero instances of the block is fine for our application, so I don't want to make it an un-deletable block on the workspace at startup.

Thanks in advance,

Lyssa

Rachel Fenichel

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Sep 28, 2016, 4:01:08 PM9/28/16

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Hi Lyssa,

There's nothing built in to do that. Disabling in the toolbox if it's in the workspace sounds like the best solution.

Cheers,

Rachel

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Wolfgang Koehler

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Sep 28, 2016, 4:06:54 PM9/28/16

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I created this:
//************************************
//find all blocks on workspace by type
//************************************
function getBlocksByType(type) {
var blocks = [];
for (var blockID in workspace.blockDB_) {
    if (workspace.blockDB_[blockID].type == type) {
      blocks.push(workspace.blockDB_[blockID]);
    }
}
return(blocks);
}

and then I check if getBlocksByType(type).length > 1 in which case I do a workspace.undo(false)

Wolfgang Koehler

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Sep 28, 2016, 4:18:55 PM9/28/16

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Here is also a suggestion from Neil Fraser regarding a similar topic: "If a linear search of workspace.getAllBlocks is too slow, one suggestion is to listen to the event stream for creation and deletion events and build up a list of the blocks of the type you are interested in."

On Wednesday, September 28, 2016 at 6:00:21 PM UTC+2, Lyssa Neel wrote:

Lyssa Koton Neel

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Sep 29, 2016, 10:22:01 AM9/29/16

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Thank you Rachel and Wolfgang.
If anyone is interested, in this thread:
https://groups.google.com/forum/?hl=en#!searchin/blockly/toolbox/blockly/vkCpEzre8Lo/sv5UZJL4Bx0J
back in 2014, Andres Nebel suggested using the
Blockly.Flyout.prototype.filterForCapacity_function which is
apparently how Blockly decides to disable blocks on the toolbar.

-- Phyllis Koton Neel, Ph.D.

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Neil Fraser

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Dec 1, 2021, 2:06:53 PM12/1/21

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Note that in 2017 this issue was resolved with the addition of the 'maxInstances' map in the configuration.