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Creating a Custom Report Item Run-Time Component

The custom report item run-time component is implemented as a Microsoft .NET Framework component using any CLS-compliant language, and is called by the report processor at run time. You define the properties for the run-time component in the design environment by modifying the custom report item's corresponding design-time component.

For more information about a sample of a fully implemented custom report item, see SQL Server Reporting Services Product Samples.

Definition and Instance Objects

Before implementing a custom report item it is important to understand the difference between definition objects and instance objects. Definition objects provide the RDL representation of the custom report item whereas instance objects are the evaluated versions of the definition objects. There is only one definition object for each item on the report. When accessing properties on a definition object that contain expressions, you will get the unevaluated expression string. Instance objects contain the evaluated versions of the definition objects and can have a one-to-many relationship with an item's definition object. For example, if a report has a Tablix data region that contains a CustomReportItem in a detail row, there will be only one definition object but there will be an instance object for each row in the data region.

Implementing the ICustomReportItem Interface

To create a CustomReportItem run-time component you will need to implement the ICustomReportItem interface that is defined in the Microsoft.ReportingServices.ProcessingCore.dll:

namespace Microsoft.ReportingServices.OnDemandReportRendering
{
    public interface ICustomReportItem
    {
        void GenerateReportItemDefinition(CustomReportItem customReportItem);
void EvaluateReportItemInstance(CustomReportItem customReportItem);
    }
}

After you have implemented the ICustomReportItem interface, two method stubs will be generated for you: GenerateReportItemDefinition and EvaluateReportItemInstance. The GenerateReportItemDefinition method is called first and is used for setting definition properties and creating the ImageDefinition object that will contain both the definition and instance properties that are used for rendering the item. The EvaluateReportItemInstance method is called after the definition objects have been evaluated, and it provides the instance objects that will be used for rendering the item.

The following is an example implementation of a custom report item that renders the name of the control as an image.

namespace Microsoft.Samples.ReportingServices
{
    using System;
    using System.Collections.Generic;
    using System.Collections.Specialized;
    using System.Drawing.Imaging;
    using System.IO;
    using System.Text;
    using Microsoft.ReportingServices.OnDemandReportRendering;

    public class PolygonsCustomReportItem : ICustomReportItem
    {
        #region ICustomReportItem Members

        public void GenerateReportItemDefinition(CustomReportItem cri)
        {
            // Create the Image Definition object that will be 
            // used to render the custom report item
            cri.CreateCriImageDefinition();
            Image polygonImage = (Image)cri.GeneratedReportItem;
        }

        public void EvaluateReportItemInstance(CustomReportItem cri)
        {
            // Get the Image definition
            Image polygonImage = (Image)cri.GeneratedReportItem;

            // Create the image for the custom report item
            polygonImage.ImageInstance.ImageData = DrawImage(cri);
        }

        #endregion

        /// <summary>
        /// Creates an image of the CustomReportItem's name
        /// </summary>
        private byte[] DrawImage(CustomReportItem customReportItem)
        {
            int width = 1;          // pixels
            int height = 1;         // pixels
            int resolution = 75;    // dpi

            System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(width, height);
            bitmap.SetResolution(resolution, resolution);

            System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(bitmap);
            graphics.PageUnit = System.Drawing.GraphicsUnit.Pixel;

            // Get the Font for the Text
            System.Drawing.Font font = new System.Drawing.Font(System.Drawing.FontFamily.GenericMonospace,
                12, System.Drawing.FontStyle.Regular);

            // Get the Brush for drawing the Text
            System.Drawing.Brush brush = new System.Drawing.SolidBrush(System.Drawing.Color.LightGreen);

            // Get the measurements for the image
            System.Drawing.SizeF maxStringSize = graphics.MeasureString(customReportItem.Name, font);
            width = (int)(maxStringSize.Width + 2 * font.GetHeight(resolution));
            height = (int)(maxStringSize.Height + 2 * font.GetHeight(resolution));

            bitmap.Dispose();
            bitmap = new System.Drawing.Bitmap(width, height);
            bitmap.SetResolution(resolution, resolution);

            graphics.Dispose();
            graphics = System.Drawing.Graphics.FromImage(bitmap);
            graphics.PageUnit = System.Drawing.GraphicsUnit.Pixel;
            
            // Draw the text
            graphics.DrawString(customReportItem.Name, font, brush, font.GetHeight(resolution), 
                font.GetHeight(resolution));

            // Create the byte array of the image data
            MemoryStream memoryStream = new MemoryStream();
            bitmap.Save(memoryStream, ImageFormat.Bmp);
            memoryStream.Position = 0;
            byte[] imageData = new byte[memoryStream.Length];
            memoryStream.Read(imageData, 0, imageData.Length);

            return imageData;
        }
    }
}