70 lines
3.8 KiB
VB.net
70 lines
3.8 KiB
VB.net
Imports System.Threading.Tasks
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Public Class MyImage
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Inherits Image
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'事件
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Private _SourceData As String = ""
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Private _UseCache As Boolean = False
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Private _DownloadTask As Task
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Private FileCacheExpiredTime As TimeSpan = New TimeSpan(7, 0, 0, 0) ' 一个星期的缓存有效期
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Public Property UseCache As Boolean
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Get
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Return _UseCache
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End Get
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Set(value As Boolean)
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_UseCache = value
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End Set
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End Property
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''' <summary>
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''' 重写Image的Source属性
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''' </summary>
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Public Shadows Property Source As String
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Get
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Return _SourceData
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End Get
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Set(value As String)
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If String.IsNullOrEmpty(value) Then Exit Property
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_SourceData = value
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If Not value.StartsWithF("http") Then ' 本地资源直接使用
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MyBase.Source = New MyBitmap(_SourceData)
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Exit Property
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End If
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If _DownloadTask IsNot Nothing AndAlso Not _DownloadTask.IsCompleted Then ' 之前下载任务还在，直接砍了
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_DownloadTask.Dispose()
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End If
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Dim NeedDownload As Boolean = True '是否需要下载/本地是否有有效缓存
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Dim TempFilePath As String = PathTemp & "Cache\MyImage\" & GetHash(_SourceData) & ".png"
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If _UseCache And File.Exists(TempFilePath) And (DateTime.Now - File.GetCreationTime(TempFilePath)) < FileCacheExpiredTime Then NeedDownload = False ' 缓存文件存在且未过期，不需要重下
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If Not NeedDownload Then
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MyBase.Source = New MyBitmap(TempFilePath)
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Exit Property
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End If
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' 异步下载图片
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Dim TaskID = 0
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_DownloadTask = New Task(Sub()
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NetDownload(_SourceData, TempFilePath, True)
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End Sub)
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TaskID = _DownloadTask.Id
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_DownloadTask.Start()
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_DownloadTask.ContinueWith(Sub(t)
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If t.IsCompleted AndAlso t.Id = TaskID Then ' 任务没有被干掉
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MyBase.Source = New MyBitmap(TempFilePath)
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End If
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End Sub, TaskScheduler.FromCurrentSynchronizationContext())
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End Set
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End Property
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Public Shared Shadows ReadOnly SourceProperty As DependencyProperty = DependencyProperty.Register("Source", GetType(String), GetType(MyImage), New PropertyMetadata(New PropertyChangedCallback(
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Sub(sender As DependencyObject, e As DependencyPropertyChangedEventArgs)
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If Not IsNothing(sender) Then
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If String.IsNullOrEmpty(e.NewValue.ToString()) Then Exit Sub
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CType(sender, MyImage).Source = e.NewValue.ToString()
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End If
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End Sub)))
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End Class
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