Fix broken reimport (#166)

* Fixes broken reimport from issue #165

* Clear the cache when loading a new diagram

* Clean diff

* Add comments

Co-authored-by: jan.ladleif <jan.ladleif@hpi.uni-potsdam.de>
Co-authored-by: Jan Ladleif <jan.ladleif@hpi.de>

lib/Modeler.js

@@ -20,7 +20,8 @@ import BpmnDiOrdering from './features/di-ordering';
 import ChoreoSpaceToolModule from './features/space-tool';
 
 import {
-  displayChoreography
+  displayChoreography,
+  clearShapeCache
 } from './import/ImportHandler';
 
 
@@ -39,6 +40,11 @@ Modeler.prototype.open = function(bpmnDiagramOrId) {
   return displayChoreography(this, bpmnDiagramOrId);
 };
 
+Modeler.prototype.importXML = function(xml, bpmnDiagram) {
+  clearShapeCache();
+  return BaseModeler.prototype.importXML.call(this, xml, bpmnDiagram);
+};
+
 Modeler.prototype.clear = function() {
   // Skip clearing of the DI references introduced in this commit by bpmn-js:
   // https://github.com/bpmn-io/bpmn-js/commit/0c71ad30a0c945679851e73b15647f634f2b9bb8

lib/Viewer.js

@@ -6,7 +6,8 @@ import inherits from 'inherits';
 import CoreModule from './core';
 
 import {
-  displayChoreography
+  displayChoreography,
+  clearShapeCache
 } from './import/ImportHandler';
 
 
@@ -35,6 +36,11 @@ Viewer.prototype.open = function(bpmnDiagramOrId) {
   return displayChoreography(this, bpmnDiagramOrId);
 };
 
+Viewer.prototype.importXML = function(xml, bpmnDiagram) {
+  clearShapeCache();
+  return BaseViewer.prototype.importXML.call(this, xml, bpmnDiagram);
+};
+
 Viewer.prototype.clear = function() {
   // Skip clearing of the DI references introduced in this commit by bpmn-js:
   // https://github.com/bpmn-io/bpmn-js/commit/0c71ad30a0c945679851e73b15647f634f2b9bb8

lib/import/ImportHandler.js

@@ -1,5 +1,13 @@
 let shapeCache = {};
 
+/**
+ * Clear the cached shapes. This function should be called when loading a new diagram,
+ * since the old cache might lead to errors if elements with the same IDs are encountered.
+ */
+export function clearShapeCache() {
+  shapeCache = {};
+}
+
 /**
  * Display a specific choreography contained in the definitions attached to a viewer.
  *