Schema Lock issue when using ITable.AddField via ArcObjects

Question

During a process I am running, I sometimes need to create a field that is missing in an attribute table. Unfortunately, the program is complaining that the table I am adding the field to has a schema lock from the program itself. So I attempted to add the ISchemaLock method for granting an exclusive lock and I now get the HRESULT error 0x8004022D when attempting to change the lock. Here is what the code looks like.

private void DoWork()
{
 IWorkspace workspace = getWorkspacefromPath(workspacepath);
 IFeatureWorkspace fWorkspace = (IFeatureWorkspace)workspace;
 IFeatureClass fc = fWorkspace.OpenFeatureClass(targetfile);
 if (fc == null)
 {
 MessageBox.Show("No feature class found.", "Error.");
 return;
 }
 ITable table = (ITable)fc;
 int index = table.FindField("PSTATE");
 if (index == -1)
 {
 ISchemaLock schemaLock = (ISchemaLock)table;
 settesttext("No PSTATE field found. Adding field now.");
 try
 {
 schemaLock.ChangeSchemaLock(esriSchemaLock.esriExclusiveSchemaLock);
 table.AddField(fielddata());
 }
 catch (Exception error)
 {
 MessageBox.Show("Field creation error. Closing process." + "\n " + error.Message);
 return;
 }
 finally
 {
 schemaLock.ChangeSchemaLock(esriSchemaLock.esriSharedSchemaLock);
 }
 settesttext("Field creation complete");
 index = table.FindField("PSTATE");
}

How should I go about adding the field to avoid getting a schema lock problem?

• kenbuja: Have you tried using the geoprocessor tool AddField in your code instead?
• Nathanus: No, I have not, but this method has worked in the past. I would like to know the root cause of this error.
• blah238: What type of workspace is it (shapefile, file geodatabase, personal geodatabase, SDE)?
• Nathanus: It's a file GDB workspace. There is no other work being done on the target feature class when the process takes place. The only interaction with it is shown in the method above.
• Nathanus: Ah... figured it out. Hold on.

Answer 1

It appears that the lock was due to the IFeatureWorkspace maintaining a reference to the file GDB I was using.

Adding...

 fWorkspace = null;
 GC.Collect();

after creating the IFeatureClass instance did the trick. Thanks @blah238 for making me consider the workspace.

• blah238: Interesting. Does using Marshal.FinalReleaseComObject(fWorkspace) have the same effect?