Cr e a t in g D a t a - Aw a r e For m s in Visual Basic .NET

Creating Data Matrix ECC200 in Visual Basic .NET Cr e a t in g D a t a - Aw a r e For m s

All for m s t hat display dat a are dat a- awar e at one level or anot her . How ev er, t he m or e a form aut om at ically configur es it self t o t he dat a set behind it , t he m ore

awar e of dat a t hat form is. A form can even change t he dat a behind it in response t o t he form s envir onm ent . I r efer t o t his k ind of int eract ion bet w een a form and it s associat ed dat a as t he dat a awar eness of a form . This sect ion present s a sam ple t hat dem onst rat es a higher degree of dat a awar eness t han t he prev ious ones. I n addit ion, t he sam ple illust rat es how t o use a st or ed procedur e t hat accept s a param et er t o dynam ically cont r ol t he dat a t hat a form display s. The sam ple has t wo for m s Form 1 and Form 6 in t he My ADODOTNETSam ples solut ions. Form 1 collect s a value designat ing a count ry and passes t he value on t o Form 6 w hile opening it . When Form 6 opens, it populat es t wo Dat aTable obj ect s in a dat a set behind it . Bot h Dat aTable obj ect s v ary based on t he value passed t o t he form . I n t he first Dat aTable obj ect , t he code behind t he form uses t he passed value as t he param et er value for a st or ed procedur e. This code behind Form 6 assigns t his Dat aTable obj ect t o t he Dat aSource propert y of a com bo box . A second Dat aTable obj ect relies on a SQL st ring expr ession t hat relies on t he passed value. This t able doesn t dir ect ly populat e t hr ee dat a- bound t ext box es on Form 6. I nst ead, t he t ex t box es bind t o a Dat aView obj ect based on t he second Dat aTable but filt ered based on t he value in t he com bo box. As I said, t his sam ple act ually configures Form 6 based on t he dat a. The com bo box list s t he cit ies in a count ry, which is based on a value passed t o Form 6 from Form 1. The t hr ee t ext box es display t he Cust om erI D, Cont act Nam e, and Phone for one or m ore cust om ers wit hin t he cit y display ed in t he com bo box . Form 6 condit ionally shows nav igat ion but t ons for m ov ing am ong t he rows of cont act dat a wit hin a count ry . I f t her e aren t at least t w o cust om ers in a cit y , t he form hides t he navigat ion but t ons. I ncident ally, t his sam ple also dem onst rat es how t o const ruct nav igat ion but t ons for m oving t hrough t he r ows behind a set of dat abound t ext box es. Because t he sam ple for t his sect ion uses t wo form s, y ou ll probably want t o open bot h Form 1 and Form 6 in Design v iew . You ll also lik ely want t o v iew t he code behind each form . The sam ple begins w it h a user r esponding t o Form 1, so m ake t hat form your st art up obj ect in t he My ADODOTNETSam ples solut ion. However, befor e launching t he applicat ion successfully, y ou m ust add t he udpCit iesI nCust om ersCount r y st or ed procedure t o t he Nort hw ind dat abase. The procedur e ret urns fr om t he Cust om ers t able all t he cit ies w it hin a count ry specified by a param et er supplied at r un t im e. As is st andard pract ice, t he follow ing T- SQL script for Query Analyzer drops any pr ior v ersion of t he st ored procedur e befor e cr eat ing a new version of it . You can run t he script m ost easily from Quer y Analyzer. --Work with Northwind database. USE Northwind GO --Remove any prior version of --udpCitiesInCustomersCountry. IF EXISTS (SELECT ROUTINE_NAME FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_TYPE = PROCEDURE AND ROUTINE_NAME = udpCitiesInCustomersCountry ) DROP PROCEDURE udpCitiesInCustomersCountry GO --Create new version of udpCitiesInCustomersCountry. CREATE PROC udpCitiesInCustomersCountry @country nvarchar (15) = USA AS SELECT DISTINCT City FROM Customers WHERE Country = @country GO

Aft er running t he sam ple in t his sect ion, y ou can rer un t he port ion of t he preceding script t o drop t he udpCit iesI nCust om ersCount r y st or ed procedur e from t he Nort hw ind dat abase. This act ion w ill allow y ou t o preserv e t he init ial design of t he Nort hw ind dat abase. Figur e 10- 14 shows For m 1 on t he left wit h Brazil ent ered as t he count r y. Clicking t he Open Form 6 but t on opens Form 6 as shown in t he upper right of t he figur e. I nit ially, t he cit y Cam pinas appears in t he com bo box. Not ice t hat no navigat ional but t ons appear below t he t ex t boxes. This is because t her e is j ust one cust om er locat ed in Cam pinas. The com bo box in Form 6 is open t o m ak e S o Paulo t he select ed cit y. The v iew of Form 6 in t he lower right of Figur e 10- 14 shows S o Paulo select ed in t he com bo box, wit h nav igat ional but t ons below t he t ext box es because t he Cust om ers t able has four cust om er s sit uat ed in S o Paulo. Figu r e 1 0 - 1 4 . Th is e x am p le of a d a t a - aw a r e for m displa ys n a viga t ion a l bu t t on s only w h e n t h e re is m or e t h an on e cu st om e r in a cit y t o view . Com bo b ox se le ct ion s ch an ge t h e se t of cit ie s t h a t t h e t e xt b ox e s ca n sh ow .

Not ice also t he form bor ders in Figure 10- 14. Form 1 appears w it h no border. Form 6 appears wit h a capt ion, but it has no built - in Minim ize, Max im ize, or Close but t on. Bot h form s requir e users t o close a form t hrough t he cust om cont rol on t he form t hat enables t he form close funct ion. This feat ur e is especially appropriat e in t his design because using t he st andard but t ons can fail t o close t he

applicat ion proper ly. I w ill descr ibe br iefly t he t wo t echniques for m anaging t he look of t he form s in rev iew ing t he code behind each form . Th e Code Be h ind For m 1 The code behind Form 1 consist s of t hr ee short event pr ocedur es. The form Load ev ent set s t he Form Border St y le pr opert y t o None. This r em ov es any sign of a st andard w indow border . I n t he process, it r em oves t he built - in Close but t on, which w as t he m ain obj ect iv e of t he pr opert y assignm ent for t his applicat ion. Users can st ill close t he for m w it h t he cust om but t on labeled Close. This rem ov es t he form in a way t hat clears any t race of t he applicat ion. But t on1 is labeled Open Form 6. Click ing t his but t on act ually does a lit t le m or e. First it inst ant iat es an inst ance of Form 6 so t hat it can assign a value t o a public variable nam ed Count ry in t he Form 6 class inst ance. The ev ent pr ocedur e copies t he cont ent s of t he Text propert y for Text Box1 t o t he Count ry variable in t he Form 6 inst ance. Aft er assigning a value t o t he Count ry var iable, t he ev ent procedur e opens t he applicat ion s second form by inv ok ing t he Show m et hod for t he frm 6 inst ance. Just befor e t he ev ent pr ocedur e concludes, it hides t he cur r ent for m . The ev ent procedure for t he Close but t on ex it s t he ent ir e applicat ion w it h t he Exit m et hod for t he Applicat ion obj ect . An Applicat ion obj ect s Ex it m et hod closes all windows for an applicat ion, but it doesn t invok e any special code associat ed w it h t he Close ev ent or t he Closing event for a form inst ance. Therefore, if y ou have explicit t erm inat ion code associat ed w it h t hose ev ent s, run t he Close m et hod for any form t hat requires t he code t o r un before invok ing t he Exit m et hod for t he Applicat ion obj ect . Private Sub Form1_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load Reset border to remove Close button. Me.FormBorderStyle = FormBorderStyle.None End Sub Private Sub Button1_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles Button1.Click Dim frm6 As New Form6() Open Form6 and hide Form1. frm6.Country = TextBox1.Text frm6.Show() Me.Hide() End Sub Private Sub Button2_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles Button2.Click Exit application. Application.Exit() End Sub