How to trigger conduit clear on input disconnect?

Grasshopper Developer
2

Hi everyone,

From this " Clear display memory once there are no inputs - Grasshopper Component Display - Grasshopper Developer - McNeel Forum" I understand, that SolveInstance() isn’t called on a component if a required input is disconnected. This means any logic within SolveInstance() to handle a disconnected state won’t execute. The correct method is to use BeforeSolveInstance(), which is always called before each solution, regardless of input validity.

  using System;
  using System.Collections.Generic;
  using System.Drawing;
  using Grasshopper.Kernel;
  using Rhino.Geometry;
  using Rhino.Display;

  public class ClearDebug_Component : GH_Component
  {
      private TextDot _dot;

      public ClearDebug_Component()
        : base("Clear Debug", "ClearDbg",
            "A minimal component to debug preview clearing.",
            "FDM TP", "DEV")
      {
      }

      protected override void RegisterInputParams(GH_Component.GH_InputParamManager pManager)
      {
          pManager.AddPointParameter("Point", "P", "Point for text dot", GH_ParamAccess.item);
      }

      protected override void RegisterOutputParams(GH_Component.GH_OutputParamManager pManager)
      {
      }

      protected override void BeforeSolveInstance()
      {
          // Clear the preview data before each solution.
          _dot = null;
      }

      protected override void SolveInstance(IGH_DataAccess DA)
      {
          Point3d point = Point3d.Unset;
          if (!DA.GetData(0, ref point))
          {
              return;
          }

          // If the input is valid, create the preview data.
          _dot = new TextDot("Valid Input", point);
      }

      public override void DrawViewportWires(IGH_PreviewArgs args)
      {
          // Draw whatever is in our preview data.
          // If it was cleared in BeforeSolveInstance, nothing will be drawn.
          if (_dot != null)
          {
              args.Display.DrawDot(_dot, Color.Black, Color.Black, Color.Black);
          }
      }

      protected override System.Drawing.Bitmap Icon => null;
      public override Guid ComponentGuid => new Guid("c1a6c5f1-2a31-4a8e-8b6a-1b3da1b1a0e1");
  }
  1. BeforeSolveInstance() clears the preview data (_dot = null;).
  2. SolveInstance() only runs with a valid input and is responsible for creating the preview data.
  3. DrawViewportWires() draws the current preview data, which will be null if cleared.

This reliably clears the preview when the input is disconnected.