在PDF iText ASP C＃中为我的所有页面设置修复背景图像 [英] Set a fix background image for all my pages in PDF iText ASP C#

问题描述

开启按钮点击，我在我的PDF上生成4个页面，我添加了此图像以提供背景图像

On Button Click, I generate 4 pages on my PDF, i added this image to provide a background image

        string imageFilePath = parent + "/Images/bg_image.jpg";
        iTextSharp.text.Image jpg = iTextSharp.text.Image.GetInstance(imageFilePath);
        jpg.ScaleToFit(1700, 1000);
        jpg.Alignment = iTextSharp.text.Image.UNDERLYING;
        jpg.SetAbsolutePosition(0, 0);
        document.Add(jpg);

它仅适用于1页，但是当我生成包含许多记录并且有多个页面的PDF时，bg图像仅在最后一页。我想将背景图像应用到所有页面。

It works only with 1 page, but when i generate a PDF that contains many records and have several pages, the bg image is only at the last page. I want to apply the background image to all of the pages.

推荐答案

背景只添加一次是正常的，因为你只需要添加一次。

It is normal that the background is added only once, because you're adding it only once.

如果你想为每个页面添加内容，你不应该手动手动，因为你不要知道iText何时会创建新页面。相反，您应该使用页面事件。 本书第5章对此进行了解释（对于C＃版本的示例） ，请参阅 http://tinyurl.com/itextsharpIIA2C05 。）

If you want to add content to every page, you should not do that manually because you don't know when a new page will be created by iText. Instead you should use a page event. This is explained in Chapter 5 of my book (for the C# version of the examples, see http://tinyurl.com/itextsharpIIA2C05 ).

在第6章的文具示例中可以找到一个很好的示例： Stationery.cs

A nice example can be found in the Stationery example in chapter 6: Stationery.cs

想法是创建 PdfPageEvent 接口的实现，例如扩展 PdfPageEventHelper class并覆盖 OnEndPage（）方法：

The idea is to create an implementation of the PdfPageEvent interface, for instance by extending the PdfPageEventHelper class and overriding the OnEndPage() method:

class TemplateHelper : PdfPageEventHelper {
    private Stationery instance;
    public TemplateHelper() { }
    public TemplateHelper(Stationery instance) { 
        this.instance = instance;
    }
    /**
     * @see com.itextpdf.text.pdf.PdfPageEventHelper#onEndPage(
     *      com.itextpdf.text.pdf.PdfWriter, com.itextpdf.text.Document)
     */
    public override void OnEndPage(PdfWriter writer, Document document) {
        writer.DirectContentUnder.AddTemplate(instance.page, 0, 0);
    }
}

在这种情况下，我们添加 PdfTemplate ，但很容易添加 Image 替换文具实例使用 Image 实例并使用 AddImage（）替换 AddTemplate（）方法方法。

In this case, we add a PdfTemplate, but it is very easy to add an Image replacing the Stationery instance with an Image instance and replacing the AddTemplate() method with the AddImage() method.

一旦你有自定义页面事件的实例，你需要将它声明为 PdfWriter instance：

Once you have an instance of your custom page event, you need to declare it to the PdfWriter instance:

writer.PageEvent = new TemplateHelper(this);

从那一刻开始，你的 OnEndPage（）方法。

From that moment on, your OnEndPage() method will be executed each time a page is finalized.

警告：如您所记录的不得使用 OnStartPage（）在页面事件中添加内容的方法！

Warning: as documented you shall not use the OnStartPage() method to add content in a page event!

更新：

最终结果看起来或多或少如下：

The final result would look more or less like this:

class ImageBackgroundHelper : PdfPageEventHelper {
    private Image img;
    public ImageBackgroundHelper(Image img) { 
        this.img = img;
    }
    /**
     * @see com.itextpdf.text.pdf.PdfPageEventHelper#onEndPage(
     *      com.itextpdf.text.pdf.PdfWriter, com.itextpdf.text.Document)
     */
    public override void OnEndPage(PdfWriter writer, Document document) {
        writer.DirectContentUnder.AddImage(img);
    }
}

现在你可以像这样使用这个事件：

Now you can use this event like this:

string imageFilePath = parent + "/Images/bg_image.jpg";
iTextSharp.text.Image jpg = iTextSharp.text.Image.GetInstance(imageFilePath);
jpg.ScaleToFit(1700, 1000);
jpg.SetAbsolutePosition(0, 0);
writer.PageEvent = new ImageBackgroundHelper(jpg);

请注意，1700和1000似乎相当大。您确定这些是您网页的尺寸吗？

Note that 1700 and 1000 seems quite big. Are you sure those are the dimensions of your page?

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