Hide results table if no data is available.

problem_builder/public/css/student_answers_dashboard.css

@@ -21,6 +21,9 @@
 .data-export-field-container {
     margin-bottom: 1em;
 }
+.data-export-results {
+    display: none;
+}
 .data-export-results table {
     margin-top: 1em;
     border: 2px solid gray;

problem_builder/public/js/student_answers_dashboard.js

@@ -13,6 +13,7 @@ function StudentAnswersDashboardBlock(runtime, element) {
     var $blockTypes = $element.find("select[name='block_types']");
     var $rootBlockId = $element.find("input[name='root_block_id']");
     var $username = $element.find("input[name='username']");
+    var $resultTable = $element.find('.data-export-results');
 
     var status;
     function getStatus() {
@@ -45,6 +46,20 @@ function StudentAnswersDashboardBlock(runtime, element) {
         );
     }
 
+    function hideResults() {
+        $resultTable.hide();
+    }
+
+    function showResults() {
+        $resultTable.show();
+    }
+
+    function maybeShowResults() {
+        if (status.last_export_result) {
+            showResults();
+        }
+    }
+
     function handleError(data) {
         // Shim to make the XBlock JsonHandlerError response work with our format.
         status = {'last_export_result': JSON.parse(data.responseText), 'export_pending': false};
@@ -87,9 +102,9 @@ function StudentAnswersDashboardBlock(runtime, element) {
             }
 
             // Display results
-            var $resultTable = $('.data-export-results table tbody');
+            var $resultTableBody = $resultTable.find('tbody');
 
-            $resultTable.empty();
+            $resultTableBody.empty();
 
             _.each(status.last_export_result.display_data, function(row) {
 
@@ -99,9 +114,11 @@ function StudentAnswersDashboardBlock(runtime, element) {
                     tr.append($('<td>').text(cell));
                 });
 
-                $resultTable.append(tr);
+                $resultTableBody.append(tr);
             });
 
+            showResults();
+
         } else {
             if (status.export_pending) {
                 $statusArea.append($('<p>').text(
@@ -144,6 +161,10 @@ function StudentAnswersDashboardBlock(runtime, element) {
     addHandler($cancelButton, 'cancel_export');
     addHandler($deleteButton, 'delete_export');
 
+    $startButton.on('click', hideResults);
+    $cancelButton.on('click', maybeShowResults);
+    $deleteButton.on('click', hideResults);
+
     $downloadButton.on('click', function() {
         window.location.href = status.download_url;
     });