Question

我正在努力将URI绑定到图像，我的绑定工作正常。问题是图像是在运行中生成的，并且生成可能会引发异常。我正在使用转换器，但我似乎无法正确附加到DecodeFailed事件，无论是那还是我还缺少其他东西。这是我的代码：

Public Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.Convert
        Dim image As New System.Windows.Media.Imaging.BitmapImage()
        Try
            image = New System.Windows.Media.Imaging.BitmapImage(New Uri(CStr(value)))
            AddHandler image.DownloadFailed, AddressOf DecodeFailed
            AddHandler image.DecodeFailed, AddressOf DecodeFailed
        Catch
            Return Windows.DependencyProperty.UnsetValue
        End Try
        Return image
    End Function

    Private Sub DecodeFailed(ByVal sender As Object, ByVal e As System.Windows.Media.ExceptionEventArgs)
        Dim image As System.Windows.Media.Imaging.BitmapImage = DirectCast(sender, System.Windows.Media.Imaging.BitmapImage)
        image.UriSource = New Uri("C:\Users\myUser\Desktop\errorSign.jpg")
    End Sub

当我从下载处理程序中抛出异常时，DecodeFailed或DownloadFailed都没有触发。 Coverter肯定在使用，图像正在显示。

...
<myNs:ImageConverter x:Key="ImageConverter"></myNs:ImageConverter>
...
<Image Height="125" Source="{Binding Path=Uri, Converter={StaticResource ImageConverter}}"/>

Answer 1

想出来：

Public Shared Event DownloadOrDecodeFailed(ByVal oldUri As String, ByVal newUri As String)
Public Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.Convert
            Dim image As New System.Windows.Media.Imaging.BitmapImage()
            Try
                AddHandler image.DownloadFailed, AddressOf OnDownloadOrDecodeFailed
                AddHandler image.DecodeFailed, AddressOf OnDownloadOrDecodeFailed
                image.BeginInit()
                image.UriSource = DirectCast(value, Uri)
                image.EndInit()
            Catch
                Return Windows.DependencyProperty.UnsetValue
            End Try
            Return image
        End Function

        Private Shared Sub OnDownloadOrDecodeFailed(ByVal sender As Object, ByVal e As System.Windows.Media.ExceptionEventArgs)
            Dim image As System.Windows.Media.Imaging.BitmapImage = DirectCast(sender, System.Windows.Media.Imaging.BitmapImage)
            RaiseEvent DownloadOrDecodeFailed(image.UriSource.AbsolutePath, "C:\Users\myUser\Desktop\errorSign.jpg")
        End Sub

因为事件是共享的，所以如果投掷事件的图像源是相同的，我可以附加到它并从视图模型更新图像uri。

如果下载失败，则将图像源绑定到带有错误图像的URI

1 个答案: