[RaggiTech]

كاتب المشاركة : Islam Ibrahim

سأحاول فيما يلي إضافة بعض الأمثلة عن كيفية استخدام الفئة WeakReference بشكل عملي في تطبيقاتنا

هذا مثال بسيط عبارة عن فئة تقوم بحفظ عناصر الصور داخل ال Cache

كود :

Public Class ImageCache
Private _cache As IDictionary(Of String, WeakReference) = New Dictionary(Of String, WeakReference)()
Public Function GetImage(ByVal path As String) As Image
Dim reference As WeakReference
If _cache.TryGetValue(path, reference) Then
If reference.IsAlive Then
Return DirectCast(reference.Target, Image)
Else
' image has been garbage collected
' remove reference from cache
_cache.Remove(path)
End If
End If

' not in cache, so load
Dim image__1 As Image = Image.FromFile(path)
reference = New WeakReference(image__1)
_cache.Add(path, reference)
Return image__1
End Function
End Class

هذا مثال آخر عن كيفية قراءة بيانات XML من ملف XML معين

كود :

Imports System
Imports System.Collections.Generic
Imports System.Text
Imports System.IO
Imports System.Xml

Public Class Program
Sub Main(ByVal args As String())

Dim cacheFile As New CacheXmlDocument("UIConfig.xml")
Console.WriteLine(cacheFile.GetXml())

Console.WriteLine(cacheFile.GetXml())

Console.Read()
End Sub
End Class

Public Class CacheXmlDocument

Public ReadOnly FileName As String
Private wrText As WeakReference

Public Sub New(ByVal fileName__1 As String)
FileName = fileName__1
End Sub

Private Function ReadXml() As String
'load the xml document
Dim xmlDoc As New XmlDocument()
xmlDoc.Load(FileName)
Dim xml As String = xmlDoc.InnerXml

'create the weak reference
wrText = New WeakReference(xml)
Return xml
End Function

Public Function GetXml() As String
Dim text As Object = Nothing


'you may also use wrText.IsAlive to check it has been GC'ed
If wrText IsNot Nothing Then
text = wrText.Target
End If


If text IsNot Nothing Then
Return text.ToString()
Else
Return ReadXml()
End If
End Function
End Class