generate barcode using vb.net 12: Overloads and Extensions in Visual Basic .NET

Print QR in Visual Basic .NET 12: Overloads and Extensions

12: Overloads and Extensions
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The other four tabs Authors/Names, Subjects, Keywords, and Copies manage subordinate records. The code is pretty consistent among the four different tabs, so I ll limit my comments to the Authors/Names tab (see Figure 12-9).
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The controls on this tab are quite similar to those on the ListEditRecords form; they exist to manage a set of records in a table. In this case, it s the ItemAuthor table. For the presentation list, I chose to use a ListView control instead of a standard ListBox control. By setting a ListView control s View property to Details, setting its FullRowSelect field to True, and modifying its Columns collection (see Figure 12-10), you can quickly turn it into a multicolumn listbox. When you add an item to this list, you also have to add subitems to have anything appear in all but the first column.
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Dim newItem As Windows.Forms.ListViewItem = _ AuthorsList.Items.Add("John Smith") newItem.SubItems.Add("Illustrator")
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The Add button brings up the AuthorAddLocate form, whereas the Properties button displays the ItemAuthorEdit form instead. Before any of the subordinate records can be added, the parent record must exist in the database. That is because the child records include the ID number of the parent record, and without a parent record, there is no parent ID number.
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If you look in each of the Add button routines on this form, you will find code such as the following:
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' ----- The record must be saved first. If (ActiveID = -1) Then ' ----- Confirm with the user. If (MsgBox("The item must be saved to the database " & _ "before authors or names can be added. Would you " & _ "like to save the record now ", _ MsgBoxStyle.YesNo Or MsgBoxStyle.Question, _ ProgramTitle) <> MsgBoxResult.Yes) Then Return ' ----- Verify and save the data. If (ValidateFormData( ) = False) Then Return If (SaveFormData( ) = False) Then Return End If
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If this is a brand-new NamedItem record (ActiveID = 1), this code will save it before allowing the user to add the subordinate record. Any invalid data that prevents the record from being saved will be caught in the call to ValidateFormData. Actually, the calls to both ValidateFormData and SaveFormData are the same ones that occur when the user clicks on the OK button. Normally, that triggers a return of the new record s ID number to the calling form. But what if SaveFormData gets called by
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12: Overloads and Extensions
adding an author, but then the user clicks the Cancel button (which normally returns a 1 value to indicate no record added ) To avoid that, the SaveFormData function sets a class-level variable named SessionSaved:
SessionSaved = True
This flag is cleared when the form first opens, but is set to True pretty much anytime a subordinate record changes. The NamedItem form s overridden AddRecord and EditRecord functions check for this flag before returning to the calling form.
If (Me.DialogResult = Windows.Forms.DialogResult.OK) Or _ (SessionSaved = True) Then Return ActiveID Else Return -1
There s lots of other interesting code in the NamedItem form. But at nearly 1,400 lines (not counting the related designer code), I ll have to let you investigate it on your own.
Connecting the Editors to the Main Form
OK, take a breath. That was a lot of code to go through. But if you run the program now, you won t see any difference at all. We still need to connect all of the record editors to the main form. They all connect through the LinkLabel controls on the main form s Administration panel (PanelAdmin). We need to add 12 LinkClicked event handlers to access all of the new and various forms. Go ahead and add them now to the MainForm class.
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