"Main" block

[Eric Edem]

Hey All. Has anyone discovered a good pattern for creating a main block?

What I'd like to do is describe where the program begins, along with some system-level behaviors via inputs on that block. The important thing here is that it would be the only entry point, and there could only be one of them.

The way I have approached this so far is to override the workspaceToCode() generator method, and only generate code for that block. This is a little bit funky but it does work. The thing that's missing is whether there is a good way to limit a user to one block.

Maybe some scheme where the program comes with that block by default and can't delete it or create a new one?

Best,

Eric

[nekom...@gmail.com]

Hi! I guess this is what you are looking for: workspace.addChangeListener(Blockly.Events.disableOrphans);

This will switch every block (which is not a top level block*) to its disabled state when it's not connected to a top level block. These blocks will be ignored by the Blockly.JavaScript.workspaceToCode(workspace); call.

* A block considered to be a top level block if it does not call this.setPreviousStatement(true);

Reference:  https://developers.google.com/blockly/reference/js/Blockly.Events#.disableOrphans 

[Eric Edem]

Ah nice, that's a great idea.

I guess the follow-up question I have is whether there is a way to restrict how many of a certain type of block you can have. I only want a user to describe one of these blocks, because otherwise it will be ambiguous for the system to determine which one to run.

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[nekom...@gmail.com]

You can preset a block during page load, so your users won't have to add any.

let xml_text = "<xml><block type='start_block' deletable='false' x='250' y='50'></block></xml>";

let xml = Blockly.Xml.textToDom(xml_text);

Blockly.Xml.domToWorkspace(xml, workspace);

Place this code after you've created the workspace and injected the config options.

[Sam El-Husseini]

You can use the maxInstances config to set a maximum for the number of instances of a certain block type. 

https://developers.google.com/blockly/guides/configure/web/configuration_struct

Here’s a demo:

https://google.github.io/blockly-samples/examples/max-blocks-demo/

Cheers,

Sam

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[Eric Edem]

Ok thanks a lot, these are great examples.

What ended up working the best for me is initializing the workspace with an undeletable block and removing that block from the toolbox.

Thanks,

Eric

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