Fix bug in direct printing on virtual printers

Author: Khojasteh

Docs/TPrintPreview.Methods.md

@@ -3,9 +3,11 @@ TPrintPreview Methods
 
 In addition to the standard methods of Delphi's `TScrollBox` control, the [TPrintPreview](TPrintPreview.md) control has the following extra methods:
 
-- **`procedure BeginDoc()`** \
+- **`function BeginDoc(): Boolean`** \
   Initiates a new job and creates the `Canvas`.
 
+  Returns `true` if a new job is initiated; otherwise, `false`.
+
 - **`procedure EndDoc()`** \
   Finalizes the current job.
 

Examples/General/Main.pas

@@ -471,7 +471,7 @@ procedure TMainForm.PrintPreviewChange(Sender: TObject);
   btnLastPage.Enabled := (PrintPreview.CurrentPage < PrintPreview.TotalPages);
   if PrintPreview.State in [psCreating, psInserting] then
   begin
-    // allow user to navigate generated pages while other pages are stil in progress to generate
+    // allows user to navigate the generated pages while pages are still being generated
     Application.ProcessMessages;
   end;
 end;
@@ -553,23 +553,23 @@ procedure TMainForm.GeneratePages;
     with PointFrom(mmLoMetric, 100, 100) do
       InflateRect(PageBoundsAfterMargin, -X, -Y);
     {$ENDIF}
-    BeginDoc;
-    try
-      DrawImageTextPage;
-      NewPage;
-      DrawImageOnlyPage;
-      NewPage;
-      DrawRichTextPage;
-    finally
-      EndDoc;
-    end;
+    if BeginDoc then
+      try
+        DrawImageTextPage;
+        NewPage;
+        DrawImageOnlyPage;
+        NewPage;
+        DrawRichTextPage;
+      finally
+        EndDoc;
+      end;
   end;
 end;
 
 // In this example, the code is independent of the Units property of
-// PrintPreview. If you use only one measuremnt unit for PrintPreview, you can
-// easily use constant values instead of passing them to conversion methods.
-// I also tried to write the code independent of the paper size.
+// the PrintPreview component. If you use only a fix measurement unit, you can
+// use constants instead of passing values to the conversion methods.
+// Also, the code in this example is independent of the paper size.
 
 procedure TMainForm.DrawImageTextPage;
 var
@@ -581,7 +581,7 @@ procedure TMainForm.DrawImageTextPage;
   with PrintPreview do
   begin
     R := PageBoundsAfterMargin;
-    // Let's know how many units reperesents 1cm
+    // Let's know how many units represents 1cm
     OneCM := PointFrom(mmLoMetric, 100, 100);
     // 1cm margin to look better
     InflateRect(R, -OneCM.X, -OneCM.Y);

HISTORY.md

@@ -1,3 +1,7 @@
+## Version 5.96 (October 1, 2022)
+- Fixed an exception caused by canceling the print dialog of some virtual printers when the DirectPrint property is set and the BeginDoc method is called.
+- As of now, the BeginDoc method returns a boolean to indicate whether the action was successful or not. 
+
 ## Version 5.95 (July 18, 2022)
 - Fixed a bug caused by canceling the print dialog of some virtual printers (Thanks to Paolo Righi).
 

Source/Preview.pas

@@ -6,7 +6,7 @@
 {  kambiz@delphiarea.com                                                       }
 {  http://www.delphiarea.com                                                   }
 {                                                                              }
-{  TPrintPreview v5.95                                                         }
+{  TPrintPreview v5.96                                                         }
 {  TPaperPreview v2.20                                                         }
 {  TThumbnailPreview v2.12                                                     }
 {                                                                              }
@@ -567,7 +567,7 @@   TPrintPreview = class(TScrollBox)
     procedure EndInsert(Cancel: Boolean {$IFDEF COMPILER4_UP} = False {$ENDIF});
     function BeginAppend: Boolean;
     procedure EndAppend(Cancel: Boolean {$IFDEF COMPILER4_UP} = False {$ENDIF});
-    procedure BeginDoc;
+    function BeginDoc: Boolean;
     procedure EndDoc;
     procedure NewPage;
     procedure Print;
@@ -4785,37 +4785,41 @@ procedure TPrintPreview.Clear;
   fPageList.Clear;
 end;
 
-procedure TPrintPreview.BeginDoc;
+function TPrintPreview.BeginDoc: Boolean;
 begin
+  Result := False;
   if fState = psReady then
   begin
     fPageCanvas := nil;
     if not fDirectPrint then
     begin
       Clear;
-      ChangeState(psCreating);
       if UsePrinterOptions then
         GetPrinterOptions;
-      fDirectPrinting := False;
       ReferenceDC := 0;
+      fDirectPrinting := False;
+      ChangeState(psCreating);
     end
     else
     begin
-      ChangeState(psPrinting);
-      fDirectPrinting := True;
-      fDirectPrintPageCount := 0;
       if UsePrinterOptions then
         GetPrinterOptions
       else
         SetPrinterOptions;
       Printer.Title := PrintJobTitle;
       Printer.BeginDoc;
+      if not Printer.Printing then
+        Exit;
       ReferenceDC := Printer.Handle;
+      fDirectPrintPageCount := 0;
+      fDirectPrinting := True;
+      ChangeState(psPrinting);
     end;
     UpdateExtends;
     if Assigned(fOnBeginDoc) then
       fOnBeginDoc(Self);
     NewPage;
+    Result := True;
   end
 end;