Question

有没有办法将渐变背景设置为pdfcell或段落？或者我必须使用图像吗？

Answer 1

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。我还没有探讨过其他三个名为Type1，Type2和Type3的内容。

拥有PdfShading对象后，您可以直接从该对象创建PdfShadingPattern，一旦拥有该对象，您就可以从中创建ShadingColor。 ShadingColor最终来自BaseColor，因此您应该可以在任何使用过的地方使用它。在您的情况下，您想将其分配给BackgroundColor。

下面是一个完整的WinForms应用程序，它定位于iTextSharp 5.1.1.0，它显示了一个包含两列的表格，每列都有自己的渐变背景颜色。

注意：PdfShading静态方法的（x，y）坐标是文档级而不是单元级。这意味着您可能无法重复使用PdfShading ojbects，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格事件克服此限制。

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，上述方法使用的文档级位置通常不够好。要解决此问题，您需要使用单元级别定位，并且需要使用单元格事件，因为在呈现表格本身之前不知道单元格位置。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。以下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

如果其他人仍然感兴趣我正在寻找如何使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();

Itextsharp渐变背景

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