convert array of bytes to bitmapimage

问题

I\'m going to convert array of bytes to System.Windows.Media.Imaging.BitmapImage and show the BitmapImage in an image control.

When I\'m using the first code, noting happens! no error and no image is displayed. But when I\'m using the second one it works fine! can anyone say what is going on?

first code is here:

public BitmapImage ToImage(byte[] array)
{
   using (System.IO.MemoryStream ms = new System.IO.MemoryStream(array))
   {
       BitmapImage image = new BitmapImage();
       image.BeginInit();
       image.StreamSource = ms;
       image.EndInit();
       return image;
   }
}

second code is here:

public BitmapImage ToImage(byte[] array)
{
   BitmapImage image = new BitmapImage();
   image.BeginInit();
   image.StreamSource = new System.IO.MemoryStream(array);
   image.EndInit();
   return image;
 }

回答1:

In the first code example the stream is closed (by leaving the using block) before the image is actually loaded. You must also set BitmapCacheOptions.OnLoad to achieve that the image is loaded immediately, otherwise the stream needs to be kept open, as in your second example.

public BitmapImage ToImage(byte[] array)
{
    using (var ms = new System.IO.MemoryStream(array))
    {
        var image = new BitmapImage();
        image.BeginInit();
        image.CacheOption = BitmapCacheOption.OnLoad; // here
        image.StreamSource = ms;
        image.EndInit();
        return image;
    }
}

From the Remarks section in BitmapImage.StreamSource:

Set the CacheOption property to BitmapCacheOption.OnLoad if you wish to close the stream after the BitmapImage is created.

Besides that, you can also use built-in type conversion to convert from type byte[] to type ImageSource (or the derived BitmapSource):

var bitmap = (BitmapSource)new ImageSourceConverter().ConvertFrom(array);

ImageSourceConverter is called implicitly when you bind a property of type ImageSource (e.g. the Image control's Source property) to a source property of type string, Uri or byte[].

回答2:

In the first case, you defined your MemoryStream in a using block, which causes the object to be disposed when you go out of the block. So you return a BitmapImage with a disposes (and non-existing) stream.

MemoryStreams keep no unmanaged resources, so you can leave the memory and let the GC handle the freeing process (but that's not a good practice).

来源：https://stackoverflow.com/questions/14337071/convert-array-of-bytes-to-bitmapimage

标签

wpf

bytearray

bitmapimage