This question came in by email last week:
The last two days I am struggling with adding a new LayerGroup to HostApplicationServices.WorkingDatabase.LayerFilters.Root. I simply cannot get it working. Is it possible to write a blog item with example on this?
An interesting question and it can indeed be quite tricky to understand how this works. For those of you who are ADN members, here's a DevNote covering the basics, which I've taken and extended for this post.
When working with LayerFilters, it's important to know that the Database property providing access to the list of current LayerFilters does so by value (i.e. you have to get a copy of the current set of LayerFilters, manipulate it, and then set it back on the Database object to have them picked up by the system).
The below C# code implements commands to list the existing layer filters (LLFS), create three new layer filters (CLFS), and delete a layer filter selected by the user (DLF):
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.LayerManager;
namespace LayerFilters
{
public class Commands
{
[CommandMethod("LLFS")]
static public void ListLayerFilters()
{
Document doc =
Application.DocumentManager.MdiActiveDocument;
Database db = doc.Database;
Editor ed = doc.Editor;
// List the nested layer filters
LayerFilterCollection lfc =
db.LayerFilters.Root.NestedFilters;
for (int i = 0; i < lfc.Count; ++i)
{
LayerFilter lf = lfc[i];
ed.WriteMessage(
"\n{0} - {1} (can{2} be deleted)",
i + 1,
lf.Name,
(lf.AllowDelete ? "" : "not")
);
}
}
[CommandMethod("CLFS")]
static public void CreateLayerFilters()
{
Document doc =
Application.DocumentManager.MdiActiveDocument;
Database db = doc.Database;
Editor ed = doc.Editor;
try
{
// Get the existing layer filters
// (we will add to them and set them back)
LayerFilterTree lft =
db.LayerFilters;
LayerFilterCollection lfc =
lft.Root.NestedFilters;
// Create three new layer filters
LayerFilter lf1 = new LayerFilter();
lf1.Name = "Unlocked Layers";
lf1.FilterExpression = "LOCKED==\"False\"";
LayerFilter lf2 = new LayerFilter();
lf2.Name = "White Layers";
lf2.FilterExpression = "COLOR==\"7\"";
LayerFilter lf3 = new LayerFilter();
lf3.Name = "Visible Layers";
lf3.FilterExpression =
"OFF==\"False\" AND FROZEN==\"False\"";
// Add them to the collection
lfc.Add(lf1);
lfc.Add(lf2);
lfc.Add(lf3);
// Set them back on the Database
db.LayerFilters = lft;
// List the layer filters, to see the new ones
ListLayerFilters();
}
catch (Exception ex)
{
ed.WriteMessage(
"\nException: {0}",
ex.Message
);
}
}
[CommandMethod("DLF")]
static public void DeleteLayerFilter()
{
Document doc =
Application.DocumentManager.MdiActiveDocument;
Database db = doc.Database;
Editor ed = doc.Editor;
ListLayerFilters();
try
{
// Get the existing layer filters
// (we will add to them and set them back)
LayerFilterTree lft =
db.LayerFilters;
LayerFilterCollection lfc =
lft.Root.NestedFilters;
// Prompt for the index of the filter to delete
PromptIntegerOptions pio =
new PromptIntegerOptions(
"\n\nEnter index of filter to delete"
);
pio.LowerLimit = 1;
pio.UpperLimit = lfc.Count;
PromptIntegerResult pir =
ed.GetInteger(pio);
// Get the selected filter
LayerFilter lf = lfc[pir.Value - 1];
// If it's possible to delete it, do so
if (!lf.AllowDelete)
{
ed.WriteMessage(
"\nLayer filter cannot be deleted."
);
}
else
{
lfc.Remove(lf);
db.LayerFilters = lft;
ListLayerFilters();
}
}
catch(Exception ex)
{
ed.WriteMessage(
"\nException: {0}",
ex.Message
);
}
}
}
}
Here's what happens when we run the various commands:
Command: LLFS
1 - All Used Layers (cannot be deleted)
2 - Unreconciled New Layers (cannot be deleted)
3 - Viewport Overrides (cannot be deleted)
Command: CLFS
1 - Unlocked Layers (can be deleted)
2 - White Layers (can be deleted)
3 - Visible Layers (can be deleted)
4 - All Used Layers (cannot be deleted)
5 - Unreconciled New Layers (cannot be deleted)
6 - Viewport Overrides (cannot be deleted)
Command: DLF
1 - Unlocked Layers (can be deleted)
2 - White Layers (can be deleted)
3 - Visible Layers (can be deleted)
4 - All Used Layers (cannot be deleted)
5 - Unreconciled New Layers (cannot be deleted)
6 - Viewport Overrides (cannot be deleted)
Enter index of filter to delete: 1
1 - White Layers (can be deleted)
2 - Visible Layers (can be deleted)
3 - All Used Layers (cannot be deleted)
4 - Unreconciled New Layers (cannot be deleted)
5 - Viewport Overrides (cannot be deleted)
You can see the three new filters (before you delete any with the DLF command) in the LAYER dialog. To see them work, create a bunch of layers, changing the colour of some and turning off/freezing/locking others:
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