MDL-56046 core: enable multiple sheets for flexible table

lib/classes/dataformat/spout_base.php

@@ -44,6 +44,9 @@ abstract class spout_base extends \core\dataformat\base {
     /** @var $sheettitle */
     protected $sheettitle;
 
+    /** @var $renamecurrentsheet */
+    protected $renamecurrentsheet = false;
+
     /**
      * Output file headers to initialise the download of the file.
      */
@@ -54,10 +57,9 @@ abstract class spout_base extends \core\dataformat\base {
         }
         $filename = $this->filename . $this->get_extension();
         $this->writer->openToBrowser($filename);
-        if ($this->sheettitle && $this->writer instanceof \Box\Spout\Writer\AbstractMultiSheetsWriter) {
-            $sheet = $this->writer->getCurrentSheet();
-            $sheet->setName($this->sheettitle);
-        }
+
+        // By default one sheet is always created, but we want to rename it when we call start_sheet().
+        $this->renamecurrentsheet = true;
     }
 
     /**
@@ -68,9 +70,6 @@ abstract class spout_base extends \core\dataformat\base {
      * @param string $title
      */
     public function set_sheettitle($title) {
-        if (!$title) {
-            return;
-        }
         $this->sheettitle = $title;
     }
 
@@ -80,6 +79,15 @@ abstract class spout_base extends \core\dataformat\base {
      * @param array $columns
      */
     public function start_sheet($columns) {
+        if ($this->sheettitle && $this->writer instanceof \Box\Spout\Writer\AbstractMultiSheetsWriter) {
+            if ($this->renamecurrentsheet) {
+                $sheet = $this->writer->getCurrentSheet();
+                $this->renamecurrentsheet = false;
+            } else {
+                $sheet = $this->writer->addNewSheetAndMakeItCurrent();
+            }
+            $sheet->setName($this->sheettitle);
+        }
         $this->writer->addRow(array_values((array)$columns));
     }