Itextsharp渐变背景

是的，iText和iTextSharp支持渐变色。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。还有另外三个名字叫Type1、Type2和Type3，我还没有探索过。

一旦你有了PdfShading对象，你就可以直接从中创建PdfShadingPattern，一旦有了它，你可以从中创建一个ShadingColor。ShadingColor最终是从BaseColor派生而来的，所以你应该能够在任何使用它的地方使用它。在您的情况下，您希望将其分配给BackgroundColor。

以下是一个完整的WinForms应用程序，目标是iTextSharp 5.1.1.0，显示创建了一个包含两列的表，每列都有自己的渐变背景色。

注意：PdfShading静态方法的(x，y(坐标是文档级的，而不是单元格级的。这意味着，根据渐变的大小，您可能无法重用PdfShading ojbects。在下面的这个示例之后，我将向您展示如何使用单元格事件来克服这个限制。

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，上面的方法使用文档级别的位置，这通常不够好。为了克服这一点，您需要使用单元格级别的定位，并且为此需要使用单元格事件，因为在渲染表本身之前，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并处理CellLayout方法的新类。以下是完成所有这些的更新代码：

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);
            }
        }
    }
}

如果其他人仍然感兴趣我想知道如何用渐变色给整个背景上色你可以这样做。。。。

    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();