Itextsharp 渐变背景

Question

有没有办法为pdfcell或段落设置渐变背景？或者我必须使用图像？

Answer 1

是的，iText 和 iTextSharp 支持渐变颜色。 PdfShading 对象有几个静态方法，可以为您创建不同类型的 PdfShading 对象。您可能最感兴趣的两个是 SimpleAxial 和 SimpleRadial。还有另外三个名为 Type1、Type2 和 Type3 我尚未探索。

一旦您拥有了 PdfShading 对象，您就可以直接从它创建一个 PdfShadingPattern，一旦您拥有了该对象，您就可以从它创建一个 ShadingColor。 ShadingColor 最终派生自 BaseColor，因此您应该能够在任何使用它的地方使用它。在您的情况下，您想将其分配给 BackgroundColor。

下面是一个针对 iTextSharp 5.1.1.0 的完整工作 WinForms 应用程序，它显示了创建的包含两列的表格，每列都有自己的渐变背景颜色。

注意：PdfShading 静态方法的 (x,y) 坐标是文档级别的，而不是单元格级别的。这意味着您可能无法重复使用 PdfShading 对象，具体取决于渐变的大小。在下面的示例之后，我将向您展示如何使用单元事件克服此限制。

using System;
using System.Text;
using System.Windows.Forms;
using iTextSharp.text;
using iTextSharp.text.pdf;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Test file name
            string TestFile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "Test.pdf");

            //Standard iTextSharp setup
            using (FileStream fs = new FileStream(TestFile, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                using (Document doc = new Document(PageSize.LETTER))
                {
                    using (PdfWriter w = PdfWriter.GetInstance(doc, fs))
                    {
                        //Open the document for writing
                        doc.Open();

                        //Create a shading object. The (x,y)'s appear to be document-level instead of cell-level so they need to be played with
                        PdfShading shading = PdfShading.SimpleAxial(w, 0, 700, 300, 700, BaseColor.BLUE, BaseColor.RED);

                        //Create a pattern from our shading object
                        PdfShadingPattern pattern = new PdfShadingPattern(shading);

                        //Create a color from our patter
                        ShadingColor color = new ShadingColor(pattern);

                        //Create a standard two column table
                        PdfPTable t = new PdfPTable(2);

                        //Add a text cell setting the background color through object initialization
                        t.AddCell(new PdfPCell(new Phrase("Hello")) { BackgroundColor = color });

                        //Add another cell with everything inline. Notice that the (x,y)'s have been updated
                        t.AddCell(new PdfPCell(new Phrase("World")) { BackgroundColor = new ShadingColor(new PdfShadingPattern(PdfShading.SimpleAxial(w, 400, 700, 600, 700, BaseColor.PINK, BaseColor.CYAN))) });



                        //Add the table to the document
                        doc.Add(t);

                        //Close the document
                        doc.Close();
                    }
                }
            }

            this.Close();
        }

    }
}

示例 2

如上所述，上述方法使用文档级位置，这通常不够好。为了克服这个问题，您需要使用单元格级定位，并且为此您需要使用单元格事件，因为在呈现表格本身之前单元格位置是未知的。要使用单元格事件，您需要创建一个实现 IPdfPCellEvent 的新类并处理 CellLayout 方法。下面是完成所有这些操作的更新代码：

using System;
using System.Text;
using System.Windows.Forms;
using iTextSharp.text;
using iTextSharp.text.pdf;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Test file name
            string TestFile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "Test.pdf");

            //Standard iTextSharp setup
            using (FileStream fs = new FileStream(TestFile, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                using (Document doc = new Document(PageSize.LETTER))
                {
                    using (PdfWriter w = PdfWriter.GetInstance(doc, fs))
                    {
                        //Open the document for writing
                        doc.Open();

                        //Create a standard two column table
                        PdfPTable t = new PdfPTable(2);

                        //Create an instance of our custom cell event class, passing in our main writer which is needed by the PdfShading object
                        var CE = new GradientBackgroundEvent(w);

                        //Set the default cell's event to our handler
                        t.DefaultCell.CellEvent = CE;

                        //Add cells normally
                        t.AddCell("Hello");
                        t.AddCell("World");


                        //Add the table to the document
                        doc.Add(t);

                        //Close the document
                        doc.Close();
                    }
                }
            }

            this.Close();
        }

        public class GradientBackgroundEvent : IPdfPCellEvent
        {
            //Holds pointer to main PdfWriter object
            private PdfWriter w;

            //Constructor
            public GradientBackgroundEvent(PdfWriter w)
            {
                this.w = w;
            }

            public void CellLayout(PdfPCell cell, Rectangle position, PdfContentByte[] canvases)
            {
                //Create a shading object with cell-specific coords
                PdfShading shading = PdfShading.SimpleAxial(w, position.Left, position.Bottom, position.Right, position.Top, BaseColor.BLUE, BaseColor.RED);

                //Create a pattern from our shading object
                PdfShadingPattern pattern = new PdfShadingPattern(shading);

                //Create a color from our patter
                ShadingColor color = new ShadingColor(pattern);

                //Get the background canvas. NOTE, If using an older version of iTextSharp (4.x) you might need to get the canvas in a different way
                PdfContentByte cb = canvases[PdfPTable.BACKGROUNDCANVAS];

                //Set the background color of the given rectable to our shading pattern
                position.BackgroundColor = color;

                //Fill the rectangle
                cb.Rectangle(position);
            }
        }
    }
}

Answer 2

如果还有人感兴趣
我一直在寻找如何用渐变为整个背景着色
你可以这样做......

    PdfShading shading = PdfShading.simpleAxial(writer, 0, pageH, pageW, 0,
            BaseColor.WHITE, BaseColor.LIGHT_GRAY);
    PdfShadingPattern pattern = new PdfShadingPattern(shading);
    cb.setShadingFill(pattern);
    // cb.circle(500, 500, 500);
    cb.rectangle(0, 0, pageW, pageH);
    cb.fill();