从存储文件裁剪的图像在发布模式下变为空，但在调试模式下有效

Question

我有一个从存储文件中提取裁剪图像并将其保存到另一个文件的函数的问题。 我正在使用 Visual Studio 2017，目标版本10.0.16299用于 uwp 应用。

在调试模式下，它可以工作。

在释放模式下，可变像素变为空(请参阅代码！！ 为什么？？

Private Shared Async Function GetPixelData(decoder As BitmapDecoder, startPointX As UInteger, startPointY As UInteger, width As UInteger, height As UInteger, scaledWidth As UInteger,
scaledHeight As UInteger) As Task(Of Byte())
Dim transform As New BitmapTransform()
Dim bounds As New BitmapBounds()
bounds.X = startPointX
bounds.Y = startPointY
bounds.Height = height
bounds.Width = width
transform.Bounds = bounds
transform.ScaledWidth = scaledWidth
transform.ScaledHeight = scaledHeight
Dim pix As PixelDataProvider = Await decoder.GetPixelDataAsync(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Straight, transform, ExifOrientationMode.IgnoreExifOrientation, ColorManagementMode.ColorManageToSRgb)
Dim pixels As Byte() = pix.DetachPixelData()
Return pixels
End Function

' 从存储文件中获取裁剪的图像并保存在新的存储文件中

Public Shared Async Function SaveCroppedBitmapAsync(originalImageFile As StorageFile, newImageFile As StorageFile, startPoint As Point, cropSize As Size) As Task
Dim startPointX As UInteger = CUInt(Math.Floor(startPoint.X))
Dim startPointY As UInteger = CUInt(Math.Floor(startPoint.Y))
Dim height As UInteger = CUInt(Math.Floor(cropSize.Height))
Dim width As UInteger = CUInt(Math.Floor(cropSize.Width))
Using originalImgFileStream As IRandomAccessStream = Await originalImageFile.OpenReadAsync()
Dim decoder As BitmapDecoder = Await BitmapDecoder.CreateAsync(originalImgFileStream)
If startPointX + width > decoder.PixelWidth Then
startPointX = decoder.PixelWidth - width
End If
If startPointY + height > decoder.PixelHeight Then
startPointY = decoder.PixelHeight - height
End If
Using newImgFileStream As IRandomAccessStream = Await newImageFile.OpenAsync(FileAccessMode.ReadWrite)
Dim pixels As Byte() = Await GetPixelData(decoder, startPointX, startPointY, width, height, decoder.PixelWidth,
decoder.PixelHeight)
Dim encoderID As New Guid
encoderID = Guid.Empty
Select Case newImageFile.FileType.ToLower()
Case ".png"
encoderID = BitmapEncoder.PngEncoderId
Exit Select
Case ".bmp"
encoderID = BitmapEncoder.BmpEncoderId
Exit Select
Case Else
encoderID = BitmapEncoder.JpegEncoderId
Exit Select
End Select
Dim propertySet As New BitmapPropertySet()
If decoder.PixelWidth > 3000 Or decoder.PixelHeight > 3000 Then
Dim qualityValue As New BitmapTypedValue(0.4, PropertyType.Single)
propertySet.Add("ImageQuality", qualityValue)
Else
Dim qualityValue As New BitmapTypedValue(0.7, PropertyType.Single)
propertySet.Add("ImageQuality", qualityValue)
End If
Dim bmpEncoder As BitmapEncoder = Await BitmapEncoder.CreateAsync(encoderID, newImgFileStream, propertySet)
''''''''' Exception in this point,  pixel becomes null!!!! why????
bmpEncoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Straight, width, height, decoder.DpiX, decoder.DpiY,
pixels)
Await bmpEncoder.FlushAsync()
End Using
End Using
End Function

谢谢！

Answer 1

如果在代码中创建 BitmapEncoder 对象时指定了与编码器关联的图像不支持的编码选项之一(代码中的propertySet(，则会出现错误

Dim bmpEncoder As BitmapEncoder = Await BitmapEncoder.CreateAsync(encoderID, newImgFileStream, propertySet)

您指定的propertySet可能不受支持。请参阅主题解码和编码图像元数据，

• 有关哪些图像文件类型支持哪些属性的详细信息，请参阅 Windows 属性、照片元数据策略和 WIC 图像格式本机元数据查询。

• 如果与编码器关联的图像不支持其中一个请求的属性，则 SetPropertiesAsync 将失败并显示错误代码0x88982F41。

您可以修改代码，而无需设置属性以使其正常工作：

...
Dim bmpEncoder As BitmapEncoder = Await BitmapEncoder.CreateAsync(encoderID, newImgFileStream)
Try
Await bmpEncoder.BitmapProperties.SetPropertiesAsync(propertySet)
Catch ex As Exception
Debug.WriteLine(ex.Message)
End Try
...

在">尝试捕获"部分中，如果请求的属性不受支持，则可以在调试代码中看到错误消息。