Cancel print job in case of layout error

@@ -3,6 +3,7 @@
 ## 2.1.6
 
 - Add qrcode to example
+- Cancel print job in case of layout error
 
 ## 2.1.5
 

@@ -149,7 +149,7 @@ public class PrintingPlugin extends PrintDocumentAdapter implements MethodCallHa
             }
         } catch (Exception e) {
             HashMap<String, Object> args = new HashMap<>();
-            args.put("completed", printJob.isCompleted());
+            args.put("completed", printJob != null && printJob.isCompleted());
             args.put("error", e.getMessage());
             channel.invokeMethod("onCompleted", args);
         }
@@ -182,6 +182,11 @@ public class PrintingPlugin extends PrintDocumentAdapter implements MethodCallHa
 
                 result.success(0);
                 break;
+            case "cancelJob":
+                if (callback != null) callback.onLayoutCancelled();
+                if (printJob != null) printJob.cancel();
+                result.success(0);
+                break;
             case "sharePdf":
                 sharePdf((byte[]) call.argument("doc"), (String) call.argument("name"));
                 result.success(0);

@@ -40,6 +40,11 @@ class PdfPrintPageRenderer: UIPrintPageRenderer {
         ctx?.drawPDFPage(page!)
     }
 
+    func cancelJob() {
+        pdfDocument = nil
+        lock?.unlock()
+    }
+
     func setDocument(_ data: Data?) {
         let bytesPointer = UnsafeMutablePointer<UInt8>.allocate(capacity: data?.count ?? 0)
         data?.copyBytes(to: bytesPointer, count: data?.count ?? 0)

@@ -45,6 +45,11 @@ public class SwiftPrintingPlugin: NSObject, FlutterPlugin, UIPrintInteractionCon
                 writePdf(object)
             }
             result(NSNumber(value: 1))
+        } else if call.method == "cancelJob" {
+            renderer?.cancelJob()
+            let controller = UIPrintInteractionController.shared
+            controller.dismiss(animated: true)
+            result(NSNumber(value: 1))
         } else if call.method == "sharePdf" {
             if let object = args["doc"] as? FlutterStandardTypedData {
                 sharePdf(

@@ -28,6 +28,7 @@ mixin Printing {
   static Future<void> _handleMethod(MethodCall call) async {
     switch (call.method) {
       case 'onLayout':
+        try {
           final List<int> bytes = await _onLayout(PdfPageFormat(
             call.arguments['width'],
             call.arguments['height'],
@@ -36,10 +37,19 @@ mixin Printing {
             marginRight: call.arguments['marginRight'],
             marginBottom: call.arguments['marginBottom'],
           ));
+          if (bytes == null) {
+            await _channel.invokeMethod<void>('cancelJob', <String, dynamic>{});
+            break;
+          }
           final Map<String, dynamic> params = <String, dynamic>{
             'doc': Uint8List.fromList(bytes),
           };
-        return await _channel.invokeMethod('writePdf', params);
+          await _channel.invokeMethod<void>('writePdf', params);
+        } catch (e) {
+          print('Unable to print: $e');
+          await _channel.invokeMethod<void>('cancelJob', <String, dynamic>{});
+        }
+        break;
       case 'onCompleted':
         final bool completed = call.arguments['completed'];
         final String error = call.arguments['error'];