Displaying an Image from a Database in a Windows Forms Control

The BindingManagerBase is obtained for the Employees table in the DataSet, a handler is attached to manage the PositionChanged event, and that handler is called to position the display o

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Recipe 7.8 Displaying an Image from a Database in a Windows Forms Control Problem

You need to display an image from a database in a Windows Forms control

Solution

Read the image into a byte array and load it directly into a PictureBox control with a MemoryStream

The sample code contains six event handlers:

Form.Load

Sets up the sample by filling a DataTable within a DataSet with the Employees table from the Northwind sample database The EmployeeID, LastName, and FirstName fields are bound to TextBox controls The BindingManagerBase is obtained for the Employees table in the DataSet, a handler is attached to manage the PositionChanged event, and that handler is called to position the display on the first record

BindingManagerBase.PositionChanged

Updates the PictureBox with the image for the current record This event is raised when the Position property value changes

The EmployeeID for the current record is obtained using the position information

in the BindingManagerBase object A Connection object and Command object are created and used to retrieve the Photo binary field for the employee record into a Byte array A MemoryStream object is created from the Byte array The static FromStream( ) method of the System.Drawing.Image class is used to load the image into the PictureBox from the MemoryStream

Move First Button.Click

Sets the current record of the bound controls to the first record by setting the Position property of the BindingManagerBase object to 0

Move Previous Button.Click

Sets the current record of the bound controls to the previous record by

decrementing the Position property of the BindingManagerBase object by 1 Move Next Button.Click

Sets the current record of the bound controls to the next record by incrementing the Position property of the BindingManagerBase object by 1

Move Last Button.Click

Sets the current record of the bound controls to the last record by setting the Position property of the BindingManagerBase object to the total number of records, as returned by the Count property, minus 1

The C# code is shown in Example 7-16

Example 7-16 File: DisplayDatabaseImageForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Drawing;

using System.Windows.Forms;

using System.IO;

using System.Data;

using System.Data.SqlClient;

private DataSet ds;

private SqlDataAdapter da;

private BindingManagerBase bm;

//

private void DisplayDatabaseImageForm_Load(object sender,

System.EventArgs e)

{

// Create the DataSet

ds = new DataSet( );

// Create the DataAdapter and retrieve the Employees table

String selectCommand =

"SELECT EmployeeID, LastName, FirstName FROM Employees";

da = new SqlDataAdapter(selectCommand,

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.FillSchema(ds, SchemaType.Source, "Employees");

da.Fill(ds, "Employees");

// Bind several table fields to controls

employeeIdTextBox.DataBindings.Add("Text", ds,

"Employees.EmployeeID");

lastNameTextBox.DataBindings.Add("Text", ds, "Employees.LastName"); firstNameTextBox.DataBindings.Add("Text", ds, "Employees.FirstName");

// Get the binding manager base for the Employees table

bm = BindingContext[ds, "Employees"];

// Update the image in response to each record reposition

bm.PositionChanged += new EventHandler(bm_PositionChanged);

// Update the display for the first record

bm_PositionChanged(null, null);

}

private void bm_PositionChanged(Object sender, EventArgs e)

{

// Refresh the photo displayed when the current record changes

// Get the new EmployeeID using the BindingManager

int employeeId =

(int)ds.Tables["Employees"].Rows[bm.Position]["EmployeeID"];

// Create a connection

SqlConnection conn = new SqlConnection(

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

// Create a command to retrieve the employee photo

String sqlText = "SELECT Photo FROM Employees WHERE EmployeeID=" + employeeId;

SqlCommand cmd = new SqlCommand(sqlText, conn);

// Retrieve the employee photo to a stream

conn.Open( );

Byte[] image = (Byte[])cmd.ExecuteScalar( );;

MemoryStream ms = new MemoryStream(image);

conn.Close( );

// Load the image into the PictureBox from the stream

photoPictureBox.Image = Image.FromStream(ms);

ms.Close( );

}

private void moveFirstButton_Click(object sender, System.EventArgs e)

{

bm.Position = 0;

}

private void movePreviousButton_Click(object sender, System.EventArgs e)

{

bm.Position -= 1;

}

private void moveNextButton_Click(object sender, System.EventArgs e)

{

bm.Position += 1;

}

private void moveLastButton_Click(object sender, System.EventArgs e)

{

bm.Position = bm.Count - 1;

Discussion

The Windows Forms PictureBox control displays bitmap, JPEG, metafile, or icon

images

In the solution, the image stored as a BLOB in the database is retrieved into a Byte array, which is in turn copied into a System.IO.MemoryStream object The static FromStream( ) method of the Image class creates an Image object that is loaded into the PictureBox

This example uses the modified version of Northwind, where the Photo field has been updated for all employees to remove the OLE image header For more information, see the online sample code

Binding Windows Forms Controls

The abstract BindingManagerBase class synchronizes all Windows Forms

controls (i.e., Binding objects) that are bound to the same data source so that

they display information from the object within the data source, such as a row

in a DataTable

The BindingContext class is used to instantiate a BindingManagerBase object

and either a CurrencyManager or PropertyManager object is returned

depending on the type of data source:

• The CurrencyManager class inherits from the BindingManagerBase class and maintains a pointer for the current item in a data source that implements IList, IListSource, or IBindingList Data sources do not necessarily support a current-item pointer The CurrencyManager

notifies all data-bound controls if the current item changes so that they can refresh their data

• The PropertyManager class inherits from the BindingManagerBase class

and maintains the current property of an object, rather than an object in a list

The Position property is a zero-based index that gets or sets the current position

in the underlying data source list The Count property returns the number of items in the list The Current property returns the current object in the list, which must be cast to the type of object in the underlying data source before it can be used

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