ASP'NET Database Connectivity 3

1
ASP.NET Database Connectivity 3
2
Outline

• Format GridView
• Review Do while loop
• Try and Catch blocks
• More about DataReader class
• ListItem class

3
GridView

• GridView automatically generates a column for
  every field
• AutoGenerateColumns property is True by default
• To change the display format, you need to
• set AutoGenerateColumns to False
• define columns using ltColumnsgt tag

4
ltColumnsgt

• You can
• hide columns
• change the order of the fields
• change column header
• ltBoundFieldgt
• This type of column displays text from a field in
  the data source

5
The Do While . Loop

• Do While condition is true
• statement(s)
• Loop

6
Flowchart for a Do While Loop
Is the condition true
No
Yes
Execute statements within the loop
Execute statements that follow the loop
7
The Do While . Loop

• Is executed as long as the condition is True.
• If condition is False then the next statement
  after the Loop is executed.

8
Try and Catch Blocks

• It handles exception (errors)
• When exception occurs in a Try block, a
  corresponding Catch blick catches the exception
  and handles it gracefully
• At least one Catch block or a Finally block must
  follow a Try block

9
Finally Block

• This block guaranteed to execute regardless of
  whether the try block has errors or not
• It is an ideal location to place resource-release
  code for resources (e.g. files, connections etc.)
  that are used earlier

10
DataReader class

• Methods
• Read()
• Reads the next row. Returns True if there is at
  least one row otherwise, returns False
• Close()
• Closes the data reader

11
Accessing a Column in a DataReader

• Example
• Dim dr As System.Data.OleDb.OleDbDataReader
• Lable1.Text dr(FirstName)

12
ListItem

• Properties
• Text the text displayed for the list item
• Value value associated with the list item
• Usually theyre the same
• Methods
• Add(ListItem) adds an item
• Clear removes all items