--- loncom/interface/lonhelper.pm	2005/10/11 22:05:20	1.122
+++ loncom/interface/lonhelper.pm	2005/10/17 20:21:31	1.125
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # .helper XML handler to implement the LON-CAPA helper
 #
-# $Id: lonhelper.pm,v 1.122 2005/10/11 22:05:20 albertel Exp $
+# $Id: lonhelper.pm,v 1.125 2005/10/17 20:21:31 albertel Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -2017,6 +2017,18 @@ BUTTONS
 	$mapUrl = $self->{MAP_URL};
     }
 
+    my %defaultSymbs;
+    if (defined($self->{DEFAULT_VALUE})) {
+        my $valueFunc = eval($self->{DEFAULT_VALUE});
+        die 'Error in default value code for variable ' . 
+            $self->{'variable'} . ', Perl said: ' . $@ if $@;
+        my @defaultSymbs = &$valueFunc($helper, $self);
+	if (!$multichoice && @defaultSymbs) { # only allowed 1
+	    @defaultSymbs = ($defaultSymbs[0]);
+	}
+	%defaultSymbs = map { if ($_) {($_,1) } } @defaultSymbs;
+	delete($defaultSymbs{''});
+    }
 
     # Create the composite function that renders the column on the nav map
     # have to admit any language that lets me do this can't be all bad
@@ -2065,13 +2077,21 @@ BUTTONS
 	    }
 
             $col .= "<td align='center'><input type='$inputType' name='${var}.forminput' ";
-            if (!$checked && !$multichoice) {
-                $col .= "checked='checked' ";
-                $checked = 1;
-            }
-	    if ($multichoice) { # all resources start checked; see bug 1174
-		$col .= "checked='checked' ";
-		$checked = 1;
+	    if (%defaultSymbs) {
+		my $symb=$resource->symb();
+		if (exists($defaultSymbs{$symb})) {
+		    $col .= "checked='checked' ";
+		    $checked = 1;
+		}
+	    } else {
+		if (!$checked && !$multichoice) {
+		    $col .= "checked='checked' ";
+		    $checked = 1;
+		}
+		if ($multichoice) { # all resources start checked; see bug 1174
+		    $col .= "checked='checked' ";
+		    $checked = 1;
+		}
 	    }
             $col .= "value='" . $resource_name  . "' /></td>";
 
@@ -2189,6 +2209,10 @@ selection. Defaults to false.
 If true, only active students and course personnel will be
 shown. Defaults to false.
 
+=item * B<emptyallowed>:
+
+If true, the selection of no users is allowed. Defaults to false.
+
 =back
 
 =cut
@@ -2224,6 +2248,7 @@ sub start_student {
     if (defined($token->[2]{'nextstate'})) {
         $paramHash->{NEXTSTATE} = $token->[2]{'nextstate'};
     }
+    $paramHash->{'emptyallowed'} = $token->[2]{'emptyallowed'};
     
 }    
 
@@ -2485,9 +2510,14 @@ sub postprocess {
     my $self = shift;
 
     my $result = $env{'form.' . $self->{'variable'} . '.forminput'};
-    if (!$result) {
-        $self->{ERROR_MSG} = 
-	    &mt('You must choose at least one student to continue.');
+    if (!$result && !$self->{'emptyallowed'}) {
+	if ($self->{'coursepersonnel'}) {
+	    $self->{ERROR_MSG} = 
+		&mt('You must choose at least one user to continue.');
+	} else {
+	    $self->{ERROR_MSG} = 
+		&mt('You must choose at least one student to continue.');
+	}
         return 0;
     }