当PrintVisual时，WPF DataGridColumnWidth不能正常工作

Question

我有一个在设计模式下看起来很好的ucReceipt.xml，或者在打开窗口http://prntscr.com/5xl11h时看起来很好看：

        <DataGrid AutoGenerateColumns="False" ItemsSource="{Binding Receipt.ReceiptItems}" 
                  IsReadOnly="True" CanUserSortColumns="False" CanUserResizeColumns="False"
                  RowHeaderWidth="0" Grid.Row="4">
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding ItemNo}" Header="No" Width="0.5*" />
                <DataGridTextColumn Binding="{Binding cloth.Name}" Header="Description" Width="*" />
                <DataGridTextColumn Binding="{Binding Quantity}" Header="Qty" Width="auto">
                    <DataGridTextColumn.CellStyle>
                        <Style>
                            <Setter Property="TextBlock.HorizontalAlignment" Value="Stretch" />
                            <Setter Property="TextBlock.TextAlignment" Value="Right" />
                        </Style>
                    </DataGridTextColumn.CellStyle>
                </DataGridTextColumn>
                <DataGridTextColumn Binding="{Binding UnitPrice}" Header="Price" Width="auto">
                    <DataGridTextColumn.CellStyle>
                        <Style>
                            <Setter Property="TextBlock.HorizontalAlignment" Value="Stretch" />
                            <Setter Property="TextBlock.TextAlignment" Value="Right" />
                        </Style>
                    </DataGridTextColumn.CellStyle>
                </DataGridTextColumn>
                <DataGridTextColumn Binding="{Binding SubTotal}" Header="Amount" Width="auto">
                    <DataGridTextColumn.CellStyle>
                        <Style>
                            <Setter Property="TextBlock.HorizontalAlignment" Value="Stretch" />
                            <Setter Property="TextBlock.TextAlignment" Value="Right" />
                        </Style>
                    </DataGridTextColumn.CellStyle>
                </DataGridTextColumn>
            </DataGrid.Columns>
        </DataGrid>

但是，当我尝试使用以下代码进行PrintVisual时，DataGridColumns不能很好地调整大小http://prntscr.com/5xl1ds

                if (SelectReceiptWindow.SelectedReceipt != null)
                {
                    Receipt = SelectReceiptWindow.SelectedReceipt;
                    if (ReceiptWindow == null)
                        ReceiptWindow = new ReceiptViewModel();
                    ReceiptWindow.Receipt = Receipt;
                    ReceiptWindow.IsOpen = true;

                    // FIXME!!! remove after implementing CloseCmd
                    if (ReceiptWindow.IsOpen)
                        ReceiptWindow.IsOpen = false;

                    switch(ReceiptWindow.ReceiptActions)
                    {
                        case 1: // print Receipt
                            System.Windows.Controls.PrintDialog dlg = new System.Windows.Controls.PrintDialog();
                            ucReceipt r = new ucReceipt();
                            r.Width = 300;
                            r.Height = 600;
                            r.DataContext = ReceiptWindow;
                            dlg.ShowDialog();
                            dlg.PrintVisual((System.Windows.Media.Visual)r, "Receipt");
                            break;

                    }
                }

有什么想法吗？