打印预览UWP

Question

我创造了一个用文字和图像打印的工作表.唯一的问题是，如果我第一次启动打印界面，图像不会出现在打印预览中.这样我就能在预览中看到图像了吗？

MainPage.xaml：

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Button x:Name="btnPrint" Click="btnPrint_Click" Content="Print" HorizontalAlignment="Center" Margin="0,0,0,0" VerticalAlignment="Center"/>
</Grid>

MainPage.xaml.cs：

public sealed partial class MainPage : Page
{
    PrintManager printmgr = PrintManager.GetForCurrentView();
    PrintDocument printDoc = null;
    PrintTask task = null;

    public MainPage()
    {
        this.InitializeComponent();
        printmgr.PrintTaskRequested += Printmgr_PrintTaskRequested;
    }
    private void Printmgr_PrintTaskRequested(PrintManager sender, PrintTaskRequestedEventArgs args)
    {
        var deferral = args.Request.GetDeferral();
        task = args.Request.CreatePrintTask("Print", OnPrintTaskSourceRequrested);
        PrintTaskOptionDetails printDetailedOptions = PrintTaskOptionDetails.GetFromPrintTaskOptions(task.Options);
        deferral.Complete();
    }

    private async void OnPrintTaskSourceRequrested(PrintTaskSourceRequestedArgs args)
    {
        var def = args.GetDeferral();
        await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal,
          () =>
          {
              args.SetSource(printDoc?.DocumentSource);
          });
        def.Complete();
    }

    private void PrintDic_AddPages(object sender, AddPagesEventArgs e)
    {
        printDoc.AddPage(new PageToPrint());
        printDoc.AddPagesComplete();
    }
    private void PrintDic_Paginate(object sender, PaginateEventArgs e)
    {
        PrintTaskOptions opt = task.Options;
        PrintTaskOptionDetails printDetailedOptions = PrintTaskOptionDetails.GetFromPrintTaskOptions(e.PrintTaskOptions);
        printDoc.SetPreviewPageCount(1, PreviewPageCountType.Final);
    }
    private void OnGetPreviewPage(object sender, GetPreviewPageEventArgs e)
    {
        Page page = new PageToPrint();
        Grid printableArea = (Grid)page.FindName("PrintArea");
        printDoc.SetPreviewPage(e.PageNumber, printableArea);
    }

    private async void btnPrint_Click(object sender, RoutedEventArgs e)
    {
        if (printDoc != null)
        {
            printDoc.GetPreviewPage -= OnGetPreviewPage;
            printDoc.Paginate -= PrintDic_Paginate;
            printDoc.AddPages -= PrintDic_AddPages;
        }
        this.printDoc = new PrintDocument();
        printDoc.GetPreviewPage += OnGetPreviewPage;
        printDoc.Paginate += PrintDic_Paginate;
        printDoc.AddPages += PrintDic_AddPages;
        bool showPrint = await PrintManager.ShowPrintUIAsync();
    }
}

PageToPrint.xaml：

<ScrollViewer>
    <Grid x:Name="PrintArea">
        <TextBlock Text="This is the text" FontSize="80"/>
        <Image Source="Image/4.JPG"/>
    </Grid>
</ScrollViewer>

谢谢你帮忙！

Answer 1

当打印预览窗口显示时，图像似乎没有被初始化或加载。您可以尝试以下方式在预览窗口中查看图像显示。

首先，在Canvas中添加一个MainPage.xaml控件，使其Opacity="0"不能在MainPage中看到，

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Canvas Name="MyCanvas" Opacity="0"/>
    <Button x:Name="btnPrint" Click="btnPrint_Click" Content="Print" HorizontalAlignment="Center" Margin="0,0,0,0" VerticalAlignment="Center"/>
</Grid>

然后，添加一个PreparePrintContent方法并在btnPrint_Click事件中的PrintManager.ShowPrintUIAsync之前调用它，代码如下所示，

private async void btnPrint_Click(object sender, RoutedEventArgs e)
{
    if (printDoc != null)
    {
        printDoc.GetPreviewPage -= OnGetPreviewPage;
        printDoc.Paginate -= PrintDic_Paginate;
        printDoc.AddPages -= PrintDic_AddPages;
    }
    this.printDoc = new PrintDocument();
    printDoc.GetPreviewPage += OnGetPreviewPage;
    printDoc.Paginate += PrintDic_Paginate;
    printDoc.AddPages += PrintDic_AddPages;

    PreparePrintContent(new PageToPrint());

    bool showPrint = await PrintManager.ShowPrintUIAsync();
}

private void PreparePrintContent(Page pageToPrint)
{
    var canvas=(Canvas)this.FindName("MyCanvas");
    canvas.Children.Clear();
    canvas.Children.Add(pageToPrint);
}