Windows Forms

1. Windows Forms Navigating database with windows forms.

2. VB .net application Tiered applications • Provide a means to develop many presentations of the same app • Makes changes to the back end easier when it is not tied into the front end (presentation Tier)

3. Tiered Applications (Continued) • Provides more portability for code created in each business app. • Provides a way to create a Data connection that is a web service on a network. • Can easily create multiple apps for different platforms at the same time. • Apps for mobile devices • Apps for Windows • Apps for the web

4. Tiers continued • You have three basic 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 • Enforces data validation • Data Tier (Provides connections and manages rules (SQL) of the database) • The data tier can be created for any DBMS • Can be a Windows/Web service providing data to multiple apps on a network.

5. The Data tier • To create a Data Tier • Right click on the project and select new Item • Select new class • This class will contain references to the TableAdapters and DataSet • The TableAdapter contains the Connection, DataAdapters and Command Objects that are needed for the data Tier. • To access these objects and all methods and properties, require the use of Accessor methods/sub procedures that you must create

6. Data Tier (Continued) • Two methods are needed in the data tier • A function that will return a reference to the datset to the form (getDataSet()). • A sub procedure that will provide access to the Update method of the TableAdapter (setDB()) AS a refresher • All SQL statements are managed by the DataAdapter located inside the TableAdapter. • All Connections to the database are managed by the connection object which is also located inside the TableAdapter. • A local copy of the database in the DataSet

7. The Data Tier in detail

8. 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 TableAdaptertakes only the rows of data that have changed and then push them onto the database. • The Accept method of the DataSet is needs to be called once an update is performed. • The Accept method clears all flags associated with rows that have been updated.

9. 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

10. Adding and Editing Form design and changing data in a database

11. 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 • EnableNav() • EnableEdit()

12. Navigation sub procedures • When a form opens • All textboxes should be disabled and ready for navigation • Buttons that are not needed should also be disabled (i.e. Cancel button) • With the enable navigation function you have a choice of disabling the control or to make it Read only (programmer preverence) • The enable Edit will • Enable all the textboxes and disable all navigation. • By disabling navigation during edits, you prevent accidently editing a different record in the DB • The edit or Add button’s text should change to a save button. This saves on Form real estate.

13. Example code of enbleNav() PrivateSub 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 EndSub

14. Example code of enableEdit() PrivateSub 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 EndSub

15. Adding Records • The Binding Manager 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 needed in the event handler of the Add Button in order for users to add a record to the DB.

16. Example Form for adding a recod

17. 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).

18. Saving a record • There are specific steps that are taken to save a record to a database • Call the EndEdit() sub procedure in the Binding Manager object • Call the setDB() sub procedure in the DataTier • This sub procedure in the Data Tier will call the update method in the Table Adapter. • (please read tutorial on how to create the data tier) • 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

19. Edit buttons follow the same design as add