Practical Activities in VB.NET

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Figure A115
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The PictureCatalogue form
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Table A111 Control settings for the PictureCatalogue form
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Control Form ListBox
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Property Name Text Name Anchor Name SizeMode Anchor Name Text Name Text Name Text
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Setting frmCatalogue Picture Catalogue lstPictures Top, Left, Bottom picViewer StretchImage Top, Left, Right, Bottom btnAdd Add Picture btnDelete Delete Picture btnFullSize Full Size btnEdit Edit Picture
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Description
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Name to refer to it by in code The form s caption Keeps the list box snug along the left of the form Resizes the picture to t the box The picture box grows with the form Add a picture to the catalogue
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PictureBox
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Button Button Button
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Allows the picture to be displayed as big as possible For editing the picture data
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Name Text
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11 n Files, Streams and Serialization
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The code for the form is shown in Listing A113
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Public Class frmCatalogue Inherits SystemWindowsFormsForm 'The picture catalogue object Private Cat As Catalogue 'Create a catalogue, and read the XML data file if 'one exists Private Sub frmCatalogue_Load(ByVal sender As SystemObject, _ ByVal e As SystemEventArgs) _ Handles MyBaseLoad Cat = New Catalogue() If IOFileExists(FileName) Then CatReadXML(FileName) CatListCatalogue(lstPictures) End If End Sub 'This works out the filename for a data file in the same 'folder as the program See text explaining listing 1124 Private Function FileName() As String Dim fn As String fn = ApplicationExecutablePath fn = fnSubstring(0, fnLastIndexOf("\")) & _ "\Cataloguexml" Return fn End Function 'Add a picture Private Sub btnAdd_Click(ByVal sender As SystemObject, _ ByVal e As SystemEventArgs) _ Handles btnAddClick 'Get a picture file using the OpenFileDialog Dim dlg As OpenFileDialog = New OpenFileDialog() dlgInitialDirectory = "d:\Media\Photos" dlgFilter = "Photographs|*jpg|All Files|**" If dlgShowDialog() Then 'A picture has been selected 'Create it Dim P As New Picture(dlgFileName) 'Display it PDisplay(picViewer) 'Get the user to edit details PEdit() 'Add it to the catalogue CatAdd(P) 'And update the list CatListCatalogue(lstPictures) End If End Sub
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'The user has clicked on an item in the list box 'Display this picture Private Sub lstPictures_SelectedIndexChanged( _ ByVal sender As SystemObject, _ ByVal e As SystemEventArgs) _ Handles lstPicturesSelectedIndexChanged If lstPicturesSelectedItem <> "" Then Dim P As Picture P = CatRetrieve(lstPicturesSelectedItem) PDisplay(picViewer) End If End Sub 'The user has chosen to delete the current selection Private Sub btnDelete_Click( _ ByVal sender As SystemObject, _ ByVal e As SystemEventArgs) _ Handles btnDeleteClick If lstPicturesSelectedItem <> "" Then If MessageBoxShow( _ "Delete the current picture ", _ "Delete Picture", _ MessageBoxButtonsYesNo) = _ DialogResultYes Then CatRemove(lstPicturesSelectedItem) End If End If End Sub 'Closing now, so write out the data file Private Sub frmCatalogue_Closing( _ ByVal sender As Object, _ ByVal e As SystemComponentModelCancelEventArgs) _ Handles MyBaseClosing CatWriteXML(FileName) End Sub End Class Listing A113: The code for the PictureCatalogue form
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Features worth remembering
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In this exercise, we ve used a number of different techniques for le handling and user-interface creation
The Anchor property is very useful for allowing forms to be easily resized without controls disappearing or going into odd con gurations
IOFileExists() can be used to stop problems happening because an
expected le has been deleted or moved Check for it, then open it
11 n Files, Streams and Serialization
Structured XML is best dealt with from a structured collection of objects Each object can deal with its own instance data, while the collection manager simply calls on them to load and save There are a range of ways for persisting data, some are better suited to particular purposes than others Always consider the wider implications of a format you decide to use can it be repaired if it becomes corrupted (dif cult with NET streams), is it easy to pass into other software (XML is ideal), etc
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1 There are a number of glaring omissions in this application while the core of it works adequately A full-size picture view will require you to create another form with a picture box and load the picture into it If you set the picture box s SizeMode setting to AutoSize, the picture box will grow to t the image You can then use it s Resize event to change the size of the form to either the full picture size or the screen size, whichever is smaller 2 The Category property of the Picture class is currently unused, but could be used to allow groups of pictures to be displayed Examine the ListCatalogue() method of the Catalogue class This can be amended to include a given category name as a parameter so that only the matching pictures were added to the list 3 The picture data really needs a custom form for entering picture details A call to this form would be placed in the Edit() method of the Picture class pass the details to controls on the form, show the form (as a dialog), and retrieve the details when the dialog is closed