Reading and Writing Images to and from a Stream or Database

Sometimes we need to read and write images to and from a stream or database. In this example we will build an application to show how to do this for both streams and databases. We will use Microsoft Access for the database and ADO.NET to read and write data to the database.

Database Programming and ADO NET

If you are new to database programming and ADO.NET, you may want to look at the ADO.NET section of C# Corner (www.c-sharpcorner.com). Plenty of source code samples and tutorials are available for free. You also might want to check out my book for ADO.NET beginners: A Programmer's Guide to ADO.NET in C# (published by APress).

First we need to create a database. We start by creating a new Access database called AppliedAdoNet.mdb and adding a table to the database called "Users." The database table schema should look like Figure 15.7. Microsoft Access stores binary large objects (BLOBs) using the OLE object data type.

Figure 15.7. Users table schema

graphics/15fig07.jpg

To make our application a little more interactive and user-friendly, let's create a Windows application and add a text box, three button controls, and a PictureBox control. The final form looks like Figure 15.8. As you can probably guess, the Browse Image button allows users to browse for bitmap files; the Save Image button saves the image to the database; and the Read Image button reads the first row of the database table, saves binary data as a bitmap, and displays the image in the picture box.

Figure 15.8. Reading and writing images in a database form

graphics/15fig08.jpg

Before we write code on button clicks, we need to define the following variables:


 
// User-defined variables
private Image curImage = null;
private string curFileName = null;
private string connectionString =
 "Provider=Microsoft.Jet.OLEDB.4.0; " +
 "Data Source=F:\AppliedAdoNet.mdb" ;
private string savedImageName =
 "F:\ImageFromDb.BMP";

 

Do not forget to add references to the System.IO and System.Data.OleDb namespaces:


 
using System.IO;
using System.Data.OleDb;

 

The stream-related classes are defined in the System.IO namespace. We will use the OLE DB data provider, which is defined in the System.Data.OleDb namespace, to work with our Access database.

The Browse Image button click code is given in Listing 15.9, which simply browses bitmap files and saves the file name in curFileName. We can set a filter to access the file formats we want.

Listing 15.9 The Browse button click event handler

private void BrowseBtn_Click(object sender,
 System.EventArgs e)
{
 OpenFileDialog openDlg = new OpenFileDialog();
 openDlg.Filter = "All Bitmap files|*.bmp";
 string filter = openDlg.Filter;
 openDlg.Title = "Open a Bitmap File";
 if(openDlg.ShowDialog() == DialogResult.OK)
 {
 curFileName = openDlg.FileName;
 textBox1.Text = curFileName;
 }
}

The Save Image button code given in Listing 15.10 creates a FileStream object from the bitmap file, opens a connection with the database, adds a new data row, set its values, and saves the row back to the database.

Listing 15.10 The Save Image button click event handler

private void SaveImageBtn_Click(object sender,
 System.EventArgs e)
{
 // Read a bitmap's contents in a stream
 FileStream fs = new FileStream(curFileName,
 FileMode.OpenOrCreate, FileAccess.Read);
 byte[] rawData = new byte[fs.Length];
 fs.Read(rawData, 0,
 System.Convert.ToInt32(fs.Length));
 fs.Close();

 // Construct a SQL string and a connection object
 string sql = "SELECT * FROM Users";
 OleDbConnection conn = new OleDbConnection();
 conn.ConnectionString = connectionString;
 // Open the connection
 if(conn.State != ConnectionState.Open)
 conn.Open();
 // Create a data adapter and data set
 OleDbDataAdapter adapter =
 new OleDbDataAdapter(sql, conn);
 OleDbCommandBuilder cmdBuilder =
 new OleDbCommandBuilder(adapter);
 DataSet ds = new DataSet("Users");
 adapter.MissingSchemaAction =
 MissingSchemaAction.AddWithKey;

 // Fill the data adapter
 adapter.Fill(ds,"Users");

 string userDes =
 "Mahesh Chand is a founder of C# Corner ";
 userDes +=
 "Author: 1. A Programmer's Guide to ADO.NET;";
 userDes += ", 2. Applied ADO.NET. ";

 // Create a new row
 DataRow row = ds.Tables["Users"].NewRow();
 row["UserName"] = "Mahesh Chand";
 row["UserEmail"] = "mcb@mindcracker.com";
 row["UserDescription"] = userDes;
 row["UserPhoto"] = rawData;
 // Add the row to the collection
 ds.Tables["Users"].Rows.Add(row);
 // Save changes to the database
 adapter.Update(ds, "Users");
 // Clean up connection
 if(conn != null)
 {
 if(conn.State == ConnectionState.Open)
 conn.Close();
 // Dispose of connection
 conn.Dispose();
 }
 MessageBox.Show("Image Saved");
}

Once the data has been saved, the next step is to read data from the database table, save it as a bitmap again, and view the bitmap on the form. We can view an image using the Graphics.DrawImage method or using a picture box. Our example uses a picture box.

The code for reading binary data is shown in Listing 15.11. We open a connection, create a data adapter, fill a data set, and get the first row of the Users table. If you want to read all the images, you may want to modify your application or loop through all the rows. Once a row has been read, we retrieve the data stored in the UserPhoto column in a stream and save it as a bitmap file. Later we view that bitmap file in a picture box by setting its Image property to the file name.

Listing 15.11 Reading images from a database

private void ReadImageBtn_Click(object sender,
 System.EventArgs e)
{
 // Construct a SQL string and a connection object
 string sql = "SELECT * FROM Users";
 OleDbConnection conn = new OleDbConnection();
 conn.ConnectionString = connectionString;
 // Open the connection
 if(conn.State != ConnectionState.Open)
 conn.Open();
 // Create a data adapter and data set
 OleDbDataAdapter adapter =
 new OleDbDataAdapter(sql, conn);
 OleDbCommandBuilder cmdBuilder =
 new OleDbCommandBuilder(adapter);
 DataSet ds = new DataSet("Users");
 adapter.MissingSchemaAction =
 MissingSchemaAction.AddWithKey;
 // Fill the data adapter
 adapter.Fill(ds,"Users");

 // Get the first row of the table
 DataRow row = ds.Tables["Users"].Rows[0];
 // Read data in a stream
 byte[] rawData = new byte[0];
 rawData = (byte[])row["UserPhoto"];
 int len = new int();
 len = rawData.GetUpperBound(0);
 // Save rawData as a bitmap
 FileStream fs = new FileStream
 (savedImageName, FileMode.OpenOrCreate,
 FileAccess.Write);
 fs.Write(rawData, 0, len);
 // Close the stream
 fs.Close();
 // View the image in a picture box
 curImage = Image.FromFile(savedImageName);
 pictureBox1.Image = curImage;
 // Clean up connection
 if(conn != null)
 {
 if(conn.State == ConnectionState.Open)
 conn.Close();
 // Dispose of connection
 conn.Dispose();
 }
}

To see the program in action, we select the MyPhoto.bmp file by using the Browse Image button, and we click the Save Image button. When we open the database, we see that a new record has been added to the Users table. When we click on the Read Image button, a new ImageFromDb.bmp file is added to the current folder. The output is shown in Figure 15.9.

Figure 15.9. Displaying a bitmap after reading data from a database

graphics/15fig09.jpg

How to Resize Graphics When a Window Is Resized

The Control class provides a property called ClientRectangle that represents the client area of a control or form. Using this property, we can measure the size of a control or a form, and set its position on the Paint event handler or OnPaint method. Whenever a user resizes the form, OnPaint is called.


GDI+: The Next-Generation Graphics Interface

Your First GDI+ Application

The Graphics Class

Working with Brushes and Pens

Colors, Fonts, and Text

Rectangles and Regions

Working with Images

Advanced Imaging

Advanced 2D Graphics

Transformation

Printing

Developing GDI+ Web Applications

GDI+ Best Practices and Performance Techniques

GDI Interoperability

Miscellaneous GDI+ Examples

Appendix A. Exception Handling in .NET



GDI+ Programming with C#
GDI+ Programming with C#
ISBN: 073561265X
EAN: N/A
Year: 2003
Pages: 145

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