Error message on invalid block connection

[lingareddy kotanka]

Hello Team,

Greetings!

I have created some custom blocks which can be vertically stacked. and i have added types on which block can be connected next/prev.
if a user tries to connect two blocks with invalid type the block moves away. so is there any way we can show message to the user that why it cannot be connected?

Thanks in advance,

Best regards

[Neil Fraser]

That's a really good question.  I can't think of a good way using the current API.

Proposal: the move event should have a 'reason' field that records what caused the move.

* 'drag' -- User action.

* 'snap' -- Alignment to grid.

* 'bump' -- Incompatible connection type.

* undefined -- Some other move, perhaps programmatically generated.

How does that sound?  If nothing else, this would certainly make reading the log easier, since there are often a stack of up to three move events that appear all at once.  Under this proposal, you'd be able to identify the block that was bumped, but not which connection triggered the bump, nor what the other block was.

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[lingareddy kotanka]

Hello Neil Fraser,

Thanks you,

I just checked the event by logging and I do not see 'reason' field for 'move' event

I am currently using Blockly - 9.2.1

this.workspace.addChangeListener((event)=>{ console.log(event) }

[Neil Fraser]

The 'reason' property doesn't exist.  It's just a proposal.  Would it be helpful for your use case?

Sent (awkwardly) from an Android device.

To view this discussion on the web visit https://groups.google.com/d/msgid/blockly/47974204-7af6-4bd7-b7b8-22e1e35b23b4n%40googlegroups.com.

[lingareddy kotanka]

Hello Neil Fraser,

Yes, having 'reason' field would help in my case

[Beka Westberg]

Hello!

Alternatively, you could probably also detect this using a custom conection checker. The `canConnection` method calls `canConnectWithReason` which returns a number which specifies whether the connections can connect, and if not why not. So you should be able to create a custom connection checker, and then add code that informs the user of the failure to the `canConnect` method.

E.g.:

```

class MyConnectionChecker extends Blockly.ConnectionChecker {

  canConnect(a, b, isDragging, distance) {

    const reason = this.canConnectWithReason(a, b, isDragging, distance);

    switch (reason) {

      // Add surfacing information about the failure here.

    }

   return reason === Connection.CAN_CONNECT;

  }

}

```

Here's an example of creating a simple custom connection checker.

I hope that helps! If you have any further questions please reply =)

--Beka