WPF打印UIElement / Scroller多页打印始终显示相同的页面

Question

我正在尝试打印一个UIelement的卷轴，或者任何多重卷轴。

我继承自DocumentPaginator，并打印，甚至可以打印适量的页面。

问题在于它一遍又一遍地打印第一页。

这是我的分页器：

   public class MyPaginator : DocumentPaginator {
    ScrollViewer _printStuff;

    public MyPaginator(ScrollViewer document, PaperSize pageSize) {
        _printStuff = document;
        _pageSize.Height = 100; //pageSize.Height;
        _pageSize.Width = 100; //pageSize.Width;
    }

    public override DocumentPage GetPage(int pageNumber) {
        _printStuff.ScrollToVerticalOffset((PageSize.Height * pageNumber));
        _printStuff.UpdateLayout();
        DocumentPage dp = new DocumentPage(_printStuff);
        return dp;
    }

    public override bool IsPageCountValid {
        get { return true; }
    }

    private int _pageCount;
    public override int PageCount {
        get {
            if (_pageCount == 0) {
                this.ComputePageCount();
            }
            return _pageCount;
        }
    }
    private Size _pageSize;
    public override Size PageSize {
        get {
            return _pageSize;
        }
        set {
            _pageSize = value;
        }
    }

    public override IDocumentPaginatorSource Source {
        get { return null; }
    }

    public override void ComputePageCount() {
        //base.ComputePageCount();

        var totalHeight = 0d;

        if (totalHeight == 0) {
            totalHeight = _printStuff.DesiredSize.Height;
        }

        var pc = (totalHeight / PageSize.Height);
        _pageCount = (int)Math.Ceiling(pc);

    }

}

这是我的主叫代码：

        PrinterSettings ps = new PrinterSettings();
        var printDialog = new PrintDialog();
        var paginator = new MyPaginator(scroller, ps.DefaultPageSettings.PaperSize);

        printDialog.PrintDocument(paginator, "My Receipt");

这是我的用户控件：

<UserControl x:Class="TestVBS.Views.PrintTest2"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300" Name="myBox">

<ScrollViewer Name="scroller">
    <Grid Name="layout">

       <StackPanel>
            <Button Content="Button" HorizontalAlignment="Left" Margin="94,31,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click_1"/>

            <TextBlock>HEllow </TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>HEllow</TextBlock>

            <TextBlock>adsfas</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
            <TextBlock>BBBBBBBBBBBBBBBBBBBB</TextBlock>

            <TextBlock>CCCCCCCCCCCCCCCCCCC</TextBlock>
        </StackPanel>

    </Grid>
</ScrollViewer>

为什么不打印第二页，第三页和第四页？