[After writing about the extensions methods for a string][1] (the basic stuff) I was having so much fun that I decided to write another one. This time for an image. I always thought the getThumbnail method of the image class was to difficult to use and to hard to remember. So I extended Image and added a ToThumbnail method to it.
First I wrote some unittests (of course)
Imports NUnit.Framework
Imports TDB2007.Utils.CommonFunctions.Extensions
Imports System.Drawing
Namespace Extensions
''' <summary>
''' A TestClass
''' </summary>
''' <remarks></remarks>
<TestFixture()> _
Public Class TestImageExtensions
#Region " Private members "
''' <summary>
'''
''' </summary>
''' <remarks></remarks>
Private _Image As Image
''' <summary>
'''
''' </summary>
''' <remarks></remarks>
Private _NewImage As Image
#End Region
#Region " Setup and TearDown "
''' <summary>
''' Sets up the Tests
''' </summary>
''' <remarks></remarks>
<SetUp()> _
Public Sub Setup()
_Image = Nothing
_NewImage = Nothing
End Sub
''' <summary>
''' Tears down the test. Is executed after the Test is Completed
''' </summary>
''' <remarks></remarks>
<TearDown()> _
Public Sub TearDown()
End Sub
#End Region
#Region " Tests "
''' <summary>
''' A Test
''' </summary>
''' <remarks></remarks>
<Test()> _
Public Sub Test_To_see_if_thumbnail_is_created()
Dim _Graphics As Graphics
_Image = New Bitmap(100, 100)
_Graphics = Graphics.FromImage(_Image)
_Graphics.FillRectangle(Brushes.Blue, New Rectangle(0, 0, 100, 100))
_Graphics.DrawLine(Pens.Black, 10, 0, 10, 100)
Assert.IsNotNull(_Image)
_NewImage = _Image.ToThumbnail(10)
Assert.IsNotNull(_NewImage)
Assert.AreEqual(10, _NewImage.Width)
Assert.AreEqual(10, _NewImage.Height)
Assert.AreEqual(Color.FromArgb(255, 0, 0, 255), (CType(_NewImage, Bitmap)).GetPixel(0, 0))
Assert.AreEqual(Color.FromArgb(255, 0, 0, 229), (CType(_NewImage, Bitmap)).GetPixel(1, 1))
End Sub
''' <summary>
''' A Test
''' </summary>
''' <remarks></remarks>
<Test()> _
Public Sub Test_To_see_if_keepsaspectratio()
Dim _Graphics As Graphics
_Image = New Bitmap(100, 200)
_Graphics = Graphics.FromImage(_Image)
_Graphics.FillRectangle(Brushes.Blue, New Rectangle(0, 0, 100, 200))
_Graphics.DrawLine(Pens.Black, 10, 0, 10, 200)
Assert.IsNotNull(_Image)
_NewImage = _Image.ToThumbnail(20, True)
Assert.IsNotNull(_NewImage)
Assert.AreEqual(10, _NewImage.Width)
Assert.AreEqual(20, _NewImage.Height)
End Sub
''' <summary>
''' A Test
''' </summary>
''' <remarks></remarks>
<Test()> _
Public Sub Test_To_see_if_thumbnail_doesnt_keep_aspec_ratio()
Dim _Graphics As Graphics
_Image = New Bitmap(100, 200)
_Graphics = Graphics.FromImage(_Image)
_Graphics.FillRectangle(Brushes.Blue, New Rectangle(0, 0, 100, 200))
_Graphics.DrawLine(Pens.Black, 10, 0, 10, 200)
Assert.IsNotNull(_Image)
_NewImage = _Image.ToThumbnail(20, False)
Assert.IsNotNull(_NewImage)
Assert.AreEqual(20, _NewImage.Width)
Assert.AreEqual(20, _NewImage.Height)
End Sub
#End Region
End Class
End Namespace```
I even checked to see if the thumbnail was created by checking if the color of the pixels was correct. Look at how I cheated by first running the test and then seeing which color it came up with for where the black line was suppossed to be. but since the black line was very small the pixel will be another color because of loss of data.
And now for the most important part. The Extension method
```vbnet
''' <summary>
'''
''' </summary>
''' <param name="Input"></param>
''' <param name="MaximumSize"></param>
''' <param name="KeepAspectRatio"></param>
''' <returns></returns>
''' <remarks></remarks>
<Extension()> _
Public Function ToThumbnail(ByVal Input As Image, ByVal MaximumSize As Integer, Optional ByVal KeepAspectRatio As Boolean = True) As Image
Dim ReturnImage As Image
Dim _Callback As Image.GetThumbnailImageAbort = Nothing
Dim _OriginalHeight As Double
Dim _OriginalWidth As Double
Dim _NewHeight As Double
Dim _NewWidth As Double
Dim _NormalImage As Image
Dim _Graphics As Graphics
_NormalImage = New Bitmap(Input.Width, Input.Height)
_Graphics = Graphics.FromImage(_NormalImage)
_Graphics.DrawImage(Input, 0, 0, Input.Width, Input.Height)
_OriginalHeight = _NormalImage.Height
_OriginalWidth = _NormalImage.Width
If KeepAspectRatio = True Then
If _OriginalHeight > _OriginalWidth Then
If _OriginalHeight > MaximumSize Then
_NewHeight = MaximumSize
_NewWidth = _OriginalWidth / _OriginalHeight * MaximumSize
Else
_NewHeight = _OriginalHeight
_NewWidth = _OriginalWidth
End If
Else
If _OriginalWidth > MaximumSize Then
_NewWidth = MaximumSize
_NewHeight = _OriginalHeight / _OriginalWidth * MaximumSize
Else
_NewHeight = _OriginalHeight
_NewWidth = _OriginalWidth
End If
End If
Else
_NewHeight = MaximumSize
_NewWidth = MaximumSize
End If
ReturnImage = _
_NormalImage.GetThumbnailImage(Convert.ToInt32(_NewWidth), Convert.ToInt32(_NewHeight), _Callback, _
IntPtr.Zero)
_NormalImage.Dispose()
_NormalImage = Nothing
_Graphics.Dispose()
_Graphics = Nothing
_Callback = Nothing
Return ReturnImage
End Function```
And yes all the test pass. Cool huh! Perhaps not because it lacks some documentation, but then again that’s real life programming ;-).
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[1]: /index.php/DesktopDev/MSTech/vb-net-extending-string-with-extension-m
Chris is awesome.