Print Preview: Detecting plugin existence before generating the preview.

chrome/browser/resources/print_preview.js

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var localStrings = new LocalStrings();
 
 // Whether or not the PDF plugin supports all the capabilities needed for
 // print preview.
 var hasCompatiblePDFPlugin = true;
 
@@ skipping 30 matching lines @@
 
 // Destination list special value constants.
 const PRINT_TO_PDF = 'Print To PDF';
 const MANAGE_PRINTERS = 'Manage Printers';
 
 /**
  * Window onload handler, sets up the page and starts print preview by getting
  * the printer list.
  */
 function onLoad() {
+  $('system-dialog-link').addEventListener('click', showSystemDialog);
+  $('cancel-button').addEventListener('click', handleCancelButtonClick);
+  $('dummy-viewer').classList.add('hidden');
+
+  if(!checkCompatiblePluginExists()) {
+    displayErrorMessage(localStrings.getString('noPlugin'));
+    return;
+  }
+
   $('printer-list').disabled = true;
   $('print-button').disabled = true;
   $('print-button').addEventListener('click', printFile);
-  $('cancel-button').addEventListener('click', handleCancelButtonClick);
   $('all-pages').addEventListener('click', onPageSelectionMayHaveChanged);
   $('copies').addEventListener('input', copiesFieldChanged);
   $('print-pages').addEventListener('click', handleIndividualPagesCheckbox);
   $('individual-pages').addEventListener('blur', function() {
       clearTimeout(timerId);
       onPageSelectionMayHaveChanged();
   });
   $('individual-pages').addEventListener('focus', addTimerToPageRangeField);
   $('individual-pages').addEventListener('input', pageRangesFieldChanged);
   $('two-sided').addEventListener('click', handleTwoSidedClick)
   $('landscape').addEventListener('click', onLayoutModeToggle);
   $('portrait').addEventListener('click', onLayoutModeToggle);
   $('color').addEventListener('click', function() { setColor(true); });
   $('bw').addEventListener('click', function() { setColor(false); });
   $('printer-list').addEventListener(
       'change', updateControlsWithSelectedPrinterCapabilities);
-  $('system-dialog-link').addEventListener('click', showSystemDialog);
   $('increment').addEventListener('click',
                                   function() { onCopiesButtonsClicked(1); });
   $('decrement').addEventListener('click',
                                   function() { onCopiesButtonsClicked(-1); });
   $('controls').onsubmit = function() { return false; };
   chrome.send('getPrinters');
 }
 
 /**
  * Asks the browser to close the preview tab.
@@ skipping 234 matching lines @@
 function printFile() {
   chrome.send('print', [getSettingsJSON()]);
 }
 
 /**
  * Asks the browser to generate a preview PDF based on current print settings.
  */
 function requestPrintPreview() {
   isPreviewStillLoading = true;
   setControlsDisabled(true);
-  $('dancing-dots').classList.remove('hidden');
   $('dancing-dots').classList.remove('invisible');
   chrome.send('getPreview', [getSettingsJSON()]);
 }
 
 /**
  * Fill the printer list drop down.
  * Called from PrintPreviewHandler::SendPrinterList().
  * @param {Array} printers Array of printer info objects.
  * @param {number} defaultPrinterIndex The index of the default printer.
  */
@@ skipping 46 matching lines @@
   }
   pdfViewer.grayscale(!color);
 }
 
 /**
  * Display an error message in the center of the preview area.
  * @param (string) errorMessage The error message to be displayed.
  */
 function displayErrorMessage(errorMessage) {
   isPreviewStillLoading = false;
+  $('dancing-dots').classList.remove('invisible');
   $('dancing-dots-text').classList.add('hidden');
   $('error-text').innerHTML = errorMessage;
   $('error-text').classList.remove('hidden');
   setControlsDisabled(true);
 
   var pdfViewer = $('pdf-viewer');
   if (pdfViewer)
     $('mainview').removeChild(pdfViewer);
 }
 
@@ skipping 83 matching lines @@
   }
 
   var pdfPlugin = document.createElement('embed');
   pdfPlugin.setAttribute('id', 'pdf-viewer');
   pdfPlugin.setAttribute('type', 'application/pdf');
   pdfPlugin.setAttribute('src', 'chrome://print/print.pdf');
   var mainView = $('mainview');
   mainView.appendChild(pdfPlugin);
 
   // Check to see if the PDF plugin is our PDF plugin. (or compatible)
   if (!pdfPlugin.onload) {

[Lei Zhang, 2011/05/11 20:27:43]

you can probably remove this code here.

[dpapad, 2011/05/11 22:08:20]

Done. Also removed variable hasCompatiblePDFPlugin.

     hasCompatiblePDFPlugin = false;
     displayErrorMessage(localStrings.getString('noPlugin'));
     return;
   }
   pdfPlugin.onload('onPDFLoad()');
 
   // Older version of the PDF plugin may not have this method.
   // TODO(thestig) Eventually remove this check.
   if (pdfPlugin.removePrintButton) {
     pdfPlugin.removePrintButton();
   }
 
   pdfPlugin.grayscale(true);
 }
 
 /**
+ * Returns true if a compatible pdf plugin exists, false if it doesn't.
+ */
+function checkCompatiblePluginExists() {
+  var dummyPlugin = $('dummy-viewer')
+  return !!dummyPlugin.onload;
+}
+
+/**
  * Updates the state of print button depending on the user selection.
  * The button is enabled only when the following conditions are true.
  * 1) The selected page ranges are valid.
  * 2) The number of copies is valid.
  */
 function updatePrintButtonState() {
   $('print-button').disabled = (!isNumberOfCopiesValid() ||
                                 getSelectedPagesValidityLevel() != 1);
 }
 
@@ skipping 365 matching lines @@
 /**
  * Executed when the 'increment' or 'decrement' button is clicked.
  */
 function onCopiesButtonsClicked(sign) {
   if($('copies').value == 1 && (sign == -1))
     return;
   $('copies').value = getCopies() + sign * 1;
   copiesFieldChanged();
 }