Transcript txtFirstNAme.Enabled

Windows Forms
Navigating database with windows
forms.
VB .net application
Tiered application
 Provide a means to
develop many
presentations of
the same app
 Makes changes to
the back end easier
when it is not tied
into one class
Tiers continued
 You have three tiers
 Presentation (The form or front end)
 Business
 Used to make all the calculated values in
the form
 Enforces the Business rules of your
application
 Data Tier (Provides connections and
manages rules (SQL) of the database)
The Data tier
 A windows component added to your
project
 Like the form, a windows component is also
a class.
 This class will contain all the Connection,
DataAdapters and DataSets that are
needed for the data Tier.
 Each of these are considered to be private
 To access these objects and all methods and
properties, require the use of Accessor
methods/sub procedures that you must create
Data Tier (Continued)
 Two methods are needed in the data tier
1. A function that will return a reference to the
datset to the form (getDataSet()).
2. A sub procedure that will provide access to the
Update method of the DataAdapter (Update())
AS a refresher
 All SQL statements are managed by the
DataAdapter
 All Connections to the database are
managed by the connection object
 A local copy of the database in the DataSet
The Data Tier in detail
DataSets
 DataSets hold a local copy of the
database.
 Any changes of the dataset have to
be pushed back to the server
 The Update Function in the
DataAdapter takes only the rows of
data that have changed and then
push them onto the database.
DataSet Continued
 Data can change on a
DBMS on a network
frequently
 Once an update occurs,
the DataSet must accept
all changes that Occur in
the DBMS
 The AcceptChanges()
function of the datset
must be called after an
update is made
Adding and Editing
Form design and changing data in a
database
Form design for Adding records
 When adding or editing a record in
the data set
 all navigation should be disabled.
 This prevents the user from accidentally
moving the position of the record during
an edit.
 All other buttons should be disabled
 i.e. Edit and Delete buttons
 Separate sub procedures should be created
to do this
Navigation sub procedures
 When a form opens
 All textboxes should be disabled
 Buttons that are not needed should also
be disabled (i.e. Cancel button)
 This is often called enabling navigation
 There are therefore two sub
procedures that must be created
 enableNav()
 disableNav()
Example code of enbleNav()
Private Sub enableNav()
txtFirstNAme.Enabled = False
txtLastName.Enabled = False
txtAddress.Enabled = False
txtCity.Enabled = False
txtState.Enabled = False
txtZip.Enabled = False
btnNext.Enabled = True
btnPrev.Enabled = True
btnCancel.Enabled = False
End Sub
Example code of disableNav()
Private Sub disableNav()
txtFirstNAme.Enabled = True
txtLastName.Enabled = True
txtAddress.Enabled = True
txtCity.Enabled = True
txtState.Enabled = True
txtZip.Enabled = True
btnPrev.Enabled = False
btnNext.Enabled = False
btnCancel.Enabled = True
End Sub
Adding Records
 The BindingManagerBase object in
the form contains an AddNew() Sub
Procedure which
 clears all bound textboxes
 Moves the position of the record to the
end
 Auto increments all key id fields (if they
are set for auto increment)
 This sub procedure is added to the event
handler of the Add Button
Example Form for adding a recod
Adding a record continued
 Buttons can also be used for two
purposes
 With the Add button
 Click once it places the form in a position
to add a record
 Once the information is added to the text
fields, the button can be clicked again to
save the record (code provided to
student).
Saving a record
 There are specific steps that are taken to
save a record to a database
1. Call the EndCurrentEdit() sub procedure in the
BindingManagerBase object
2. Call the Update sub procedure in the
DataAdapter (located in the data tier)
3. Call the AccpetChanges sub procedure in the
DataSet (also located in the data tier)
 Taken these steps in this order will ensure
that all the data will be saved to the
database
Edit buttons follow the same design
as add