Difference between revisions of "Visual Basic .net"
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− | '''Getting just the path of a file given the entire path and filename as a string''' | + | '''Getting just the path of a file given the entire path and filename as a string'''<br /> |
<code> | <code> | ||
− | PathStr.Substring(0, ofd.FileName.LastIndexOf("\")) & "\" | + | PathStr.Substring(0, ofd.FileName.LastIndexOf("\")) & "\" |
</code> | </code> | ||
Revision as of 10:26, 27 December 2009
Contents
Graphics
setting up graphics and drawing pixels, shapes, and colours
Dim bm As New Bitmap(PictureBox1.Width, PictureBox1.Height) Dim gr As Graphics = Graphics.FromImage(bm) bm.SetPixel(10, 10, Color.FromArgb(255, 255, 0, 0)) Dim greenthickpen As New Pen(Color.FromArgb(255, 0, 255, 0), 10) gr.DrawLine(greenthickpen, 20, 20, 40, 40) gr.DrawArc(Pens.Blue, 80, 80, 20, 20, 0, 360) gr.FillPie(Brushes.Black, 150, 150, 20, 20, 0, 360) Dim rect As Rectangle rect.Width = 10 rect.Height = 10 rect.X = 200 rect.Y = 200 gr.DrawRectangle(Pens.Black, rect) Dim triangle(2) As Point triangle(0).X = 5 triangle(0).Y = 0 + 30 triangle(1).X = 0 triangle(1).Y = 5 + 30 triangle(2).X = 10 triangle(2).Y = 5 + 30 gr.FillPolygon(Brushes.Blue, triangle) PictureBox1.Image = bm
Color.FromArgb(255, 255, 0, 0) is in the format of Alpha, Red, Green, Blue
Files
Reading text files line by line
Dim f1 As Long dim filestring as string f1 = FreeFile() FileOpen(f1, My.Application.Info.DirectoryPath & "\filename.txt", OpenMode.Input) Do Until EOF(f1) filestring=LineInput(f1) Loop FileClose(f1)
Note My.Application.Info.DirectoryPath & "\filename.txt" may be replaced by "C \some_path\file.txt"
Writing text files line by line
Dim f1 As Long f1 = FreeFile() FileOpen(f1, My.Application.Info.DirectoryPath & "\filename.txt", OpenMode.Output Print(f1, "This is line 1") Print(f1, "This is line 2") FileClose(f1)
loading data files into an array of bytes
Dim oFile As System.IO.FileInfo oFile = New System.IO.FileInfo(My.Application.Info.DirectoryPath & "\file.dat") Dim oFileStream As System.IO.FileStream = oFile.OpenRead() Dim lBytes As Long = oFileStream.Length If (lBytes > 0) Then ReDim fileData(lBytes - 1) oFileStream.Read(fileData, 0, lBytes) oFileStream.Close() End If
Using a "Browse" button
Dim ofd As New OpenFileDialog dim f1 as Long If ofd.ShowDialog() = Windows.Forms.DialogResult.OK Then f1 = FreeFile() Try FileOpen(f1, ofd.FileName, OpenMode.Input) Catch ex As Exception MsgBox(ex.Message) err = 1 End Try If err = 0 Then 'read the file here End If End if
Arrays
Threading / Parallel
Distribute tasks automatically on all available cores
Imports System.Threading Imports System.Threading.Tasks Parallel.For(0, yRes - 1, Function(n) mandelbrotline(n, cr + xr, ci + yr, mandN, xRes, xStp, yStp, picarray))
n will iterate from 0 to yres -1 in no particular order
Requires .net 4 or Parallel extensions on .net 3.5
Loops
Conditionals
Math
Calling Windows API
Public Declare Function QueryPerformanceCounter Lib "kernel32.dll" (ByRef Counter As Long) As Integer Public Declare Function QueryPerformanceFrequency Lib "kernel32.dll" (ByRef counter As Long) As Integer Dim curFreq, tStart, tStop As UInt64 QueryPerformanceFrequency(curFreq) QueryPerformanceCounter(tStart) ...your code QueryPerformanceCounter(tStop) msgbox(CStr(CInt(1 / ((tStop - tStart) / curFreq))) & " Frames per second")
RS-232
sending an entire array of bytes
SerialPort1.Write(bytearray, 0, arraylength)
0 indicated the index to start reading the array, arraylength is a variable containing the number of bytes to transmit.
This operation is incredibly fast compared to looping through the array and sending 1 byte at a time. This is especially useful for high speed serial ports.
Strings
Finding text in a string
InStr("this is a string", "is")
returns (character position number) 6. This function returns 0 when not found.
Using the start of a string
dim str as string dim outputstr as string str="this is a string" outputstr=str.Substring(0, 4)
Starts at character index 0 (the first character), and reads 4 characters (including the first one), resulting in "this".
Using the middle of a string
dim str as string dim outputstr as string str="this is a string" outputstr=str.Substring(5, 4)
Starts at character index 5 (the 6th character), and reads 4 characters, resulting in "is a".
Using the end of a string
dim str as string dim outputstr as string str="this is a string" outputstr=str1.Substring(str1.Length - 4, 4)
Starts 4 chacters before the end, and reads 4 characters, resulting in "ring".
Getting just the path of a file given the entire path and filename as a string
PathStr.Substring(0, ofd.FileName.LastIndexOf("\")) & "\"
Datatypes
VB type | .net type | Size | Range |
---|---|---|---|
Boolean
|
System.Boolean
|
4 bytes | True or False |
Byte
|
System.Byte
|
1 byte | 0 to 255 (unsigned) |
SByte
|
System.SByte
|
1 byte | -128 through 127 (signed) |
Char
|
System.Char
|
2 bytes | 0 to 65535 (unsigned) |
Date
|
System.DateTime
|
8 bytes | January 1, 1 CE to December 31, 9999 |
Decimal
|
System.Decimal
|
12 bytes | +/-79,228,162,514,264,337,593,543,950,335 with no decimal point; +/-7.9228162514264337593543950335 with 28 places to the right of the decimal; smallest non-zero number is +/-0.0000000000000000000000000001 |
Double
|
System.Double
|
8 bytes | -1.79769313486231E308 to -4.94065645841247E-324 for negative values; 4.94065645841247E-324 to 1.79769313486232E308 for positive values |
Integer
|
System.Int32
|
4 bytes | -2,147,483,648 to 2,147,483,647 |
UInteger
|
System.UInt32
|
4 bytes | 0 through 4,294,967,295 (unsigned) |
Long
|
System.Int64
|
8 bytes | -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 |
ULong
|
System.UInt64
|
8 bytes | 0 through 18,446,744,073,709,551,615 (1.8...E+19) (unsigned) |
Object
|
System.Object (class)
|
4 bytes | Any type can be stored in a variable of type Object
|
Short
|
System.Int16
|
2 bytes | -32,768 to 32,767 |
UShort
|
System.UInt16
|
2 bytes | 0 through 65,535 (unsigned) |
Single
|
System.Single
|
4 bytes | -3.402823E38 to -1.401298E-45 for negative values; 1.401298E-45 to 3.402823E38 for positive values |
String
|
System.String (class)
|
10 bytes + (2 * string length) | 0 to approximately two billion Unicode characters |
User-Defined Type (structure) | (inherits from System.ValueType )
|
Sum of the sizes of its members | Each member of the structure has a range determined by its data type and independent of the ranges of the other members |