CSC 216 Useful File Programming Tips, Spring 2009

Single-line Declarations Visual Basic permits combining multiple declarations into one statement: Dim var1 as datatype, var2 As datatype, ..., varN As datatype When all variables are of the same datatype: Dim num1, num2, total as double Is there a number in the textbox? If IsNumeric(TextBox1.Text) = False Then ..... Is the number between 1 and 10? If Val(TextBox1.Text) < 1 or Val(TextBox1.Text) > 10 Then messagebox.show("Please enter a number between 1 and 10") Exit Sub Enf If User Input using InputBox Dim x as String x = InputBox("Enter a value", "Input Dialog") Number only TextBox Add the following code to a TextBox KeyPress handler: If Asc(e.KeyChar) < 48 or Asc(e.keyChar) > 57 Then e.Handled = True End If Displaying a form Enter the following code in Form1: Dim frmMyForm As New Form2() MyForm.Show() Assigning a color TextBox1.backcolor = System.Drawing.Color.Blue The intellisence feature of VB will provide you with tens of options as soon as you key in the last dot. Good Luck Assigning a color TextBox1.backcolor = System.Drawing.Color.Blue The intellisence feature of VB will provide you with tens of options as soon as you key in the last dot. Good Luck Primitive Data Types The integral value types: Byte (1-byte unsigned integer), Short (2-byte signed integer), Integer (4-byte signed integer), and Long (8-byte signed integer). These types map to System.Byte, System.Int16, System.Int32, and System.Int64, respectively. The default value of an integral type is equivalent to the literal 0. The floating-point value types: Single (4-byte floating point) and Double (8-byte floating point). These types map to System.Single and System.Double, respectively. The default value of a floating-point type is equivalent to the literal 0. The Decimal type (16-byte decimal value), which maps to System.Decimal. The default value of decimal is equivalent to the literal 0D. The Boolean value type, which represents a truth value, typically the result of a relational or logical operation. The literal is of type System.Boolean. The default value of the Boolean type is equivalent to the literal False. The Date value type, which represents a date and/or a time and maps to System.DateTime. The default value of the Date type is equivalent to the literal # 01/01/0001 12:00:00AM #. The Char value type, which represents a single Unicode character and maps to System.Char. The default value of the Char type is equivalent to the constant expression ChrW(0) Using Try...Catch blocks To avoid error messages, use Try...Catch blocks in the following manner: Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Try Dim a As Integer a = TextBox1.Text MessageBox.Show(a, Me.Text) Catch ex As Exception End Try End Sub What was the error? Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Try Dim a As Integer a = TextBox1.Text MessageBox.Show(a, Me.Text) Catch ex As Exception MessageBox.Show(ex.Message, Me.Text) TextBox1.Clear() End Try End Sub Explicit Conversions Use the methods of class Convert. Example: number = Convert.ToDouble(txtInput.Text) Locking Controls When designing the user interface of your Windows application, you can lock the controls once they are positioned correctly, so that you do not inadvertently move or resize them when setting other properties. 1) Fomat 2) Select Lock Controls Random Number Generation Numbers can be generated randomly by using class Random which is located in namespace System. Dim randObj As Random = New Random() Dim x As Integer = randomObject.Next(1, 21) Method Next, here, produces integers in the range 1-20 Method Next generates an integer value between 0 and 2147483647. When randObj is created, the current time of day becomes the seed value for the calculation. You can pass your own seed value as an argument: Dim randObj As Random = New Random(9) Good Luck TextBox/Highlight TextBox1.Focus() TextBox1.Select() Good Luck 'Sub Main' was not found Renaming the class that contains the form's implementation is done by changing the Name property of the form. However, this will display an error message saying that form1 is not found. To overcome this error: open the solution explorer right-click on the projects name select properties from the start up object drop down select the new form name Good Luck Finding all files in a directory 1) Draw a button and a listbox on the form 2) Add the line before public class: imports system.io 3) declare the variables in the button's click event Dim fileArray As String( ) Dim myFile As String 3)continue with this code fileArray = Directory.GetFiles("c:\") For Each myFile In fileArray lstData.items.add(myFile) Next Good Luck Finding all drives on a system 1) Add the following line before public class: imports system.io 2)Use a block of code similar to finding files and implement step 3 3)Use the Directory class to find for you the drives: Directory.GetLogicalDrives Good Luck Openning a Web site, a file, or a folder System.Diagnostics.Process.Start("C:\") AppendText This method appends text in the parameter to whatever exists in the text box at the time: Textbox1.AppendText("Your grade is " & grade & ControlChars.NewLine) Listing files in all directory Dim dir As New DirectoryInfo("c:\") Dim files As FileInfo() = dir.GetFiles() Dim file As FileInfo For Each file In files ListBox1.Items.Add(file.Name) Next --Try replacing Name by extension PictureBox/Run time The PictureBox is used for displaying pictures. The following lingo assumes that the file called image.bmp in the current folder. PictureBox1.Image = System.Drawing.Image.FromFile(Application.ExecutablePath & "\image.bmp") PictureBox/Design time A bitmap can be added to a PictureBox at design time. At that point, the bitmap file on disk is not needed anymore. The bitmap is now stored inside the form binary file called Form1.resx. PictureBox/Animated Gif A PictureBox accepts animated gif files. Data Type/Size/Range Byte: 1; 0 to 255 Boolean: 2; True or False Char: 2; 0 to 65535 Short: 2; -32,768 to 32,767 Integer: 4; -2,147,483,647 Single: 4; +/- 3.4E38 Object: 4; Any value Date: 8; Jan 1, 0001 to Dec 31, 9999 Double: 8; +/- 1.79E308 Long: 8; +/- 9,223,372,038,854,775,807 Decimal: 16; +/-79,228*10^24 String: 2*length; 0 to 2 billion Examples of Declarations Dim Married As Boolean Married = True Dim MiddleInitial As Char MiddleInitial = "Z" Dim BirthDate As Date BirthDate = #1/1/2002# Dim Something As Object Something = "a text message" Finding all Controls on the Form For n = 0 to Controls.Count() - 1 Listbox1.Items.Add(Controls.Items(n).Name) Next Changing font style Dim style As FontStyle style = FontStyle.Bold Or FontStyle.Italic Dim myFont As Font = New Font("ariel", 14, style) label1.Font = myFont Listbox / Inserting an item at a specific location listbox1.Items.Insert(Index, Item) Item is the object to be added Index is the location of the new item Listbox / How to avoid the insertion of identical objects in the listbox Dim strItem As String = "Hello" If not ListBox1.Items.Contains(strItem) Then Listbox1.Items.Add(strItem) End If