ImageSourceConverter抛出NullReferenceException ...为什么？

Question

I've been tearing my hair out over this issue for the last hour or so.

I have some code that goes like this:

videoTile.Icon = new ImageSourceConverter().ConvertFrom(coDrivr4.Properties.Resources.Music.GetHbitmap()) as ImageSource;

When I run my code, it says a NullReferenceException occurred. Neither 'Music' nor the return of GetHbitmap() are null.

I'm trying to get the image via the Properties because it's the only way I've figured out how to access the images in my Resources folder. I would just add them to the app.xaml file as a resource, but I'm not using an app.xaml file for a few reasons.

Am I attempting this wrong? All I need to do is get an ImageSource object of an image I have in my Resource directory. I can use them just fine in my XAML, but can't for the life of me do it in any code.

PS: I can't just add them as a resource to the XAML file because this is just a class and so there is no XAML file.

Answer 1

I hit exactly the same issue - I've got all my bitmaps in a nice, statically typed resource file and I just want to set an ImageSource with them. So, since the ImageSourceConverter was throwing null reference exceptions, I changed tack and used this piece of code instead:

Bitmap bitmap = entityCol.EntityCollectionImage;
this.Image = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(bitmap.GetHbitmap(), IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions()); // Image is an image source

Hope that helps.

Answer 2

Well you've got plenty of things which could be null in there. I suggest you separate them out:

Bitmap bitmap = coDrivr4.Properties.Resources.Music;
object source = new ImageSourceConverter().ConvertFrom(bitmap.GetHbitmap());
ImageSource imageSource = (ImageSource) source;
videoTile.Icon = imageSource;

Note the use of a cast rather than the as operator here. If source isn't an ImageSource , this will throw an InvalidCastException which will be much more descriptive than just ending up as a null reference.

EDIT: Okay, so now we know for sure that it's happening in ConvertFrom , I suggest the next step is to find out whether it's a bug in .NET 4.0 beta 1. Are you actually using any .NET 4.0 features? I suggest you try to extract just that bit of code into a separate project (you don't need to display an API, just convert the image. Try to run that code in .NET 3.5. If it fails in the same way, that's eliminated the beta-ness from the list of possible problems.

Answer 3

This is not a bug in .net Framework, this null reference exception occurs because the ImageSourceConverter cannot convert a Bitmap type object, it can to convert: Stream, string, Uri, byte[], so you have to change your code to something like this:

var imageSourceConverter = new ImageSourceConverter();
byte[] tempBitmap = BitmapToByte(eventArgs.Frame);
ImageSource image = (ImageSource)imageSourceConverter.ConvertFrom(tempBitmap);

...

private byte[] BitmapToByte(Bitmap bitmap)
{
    byte[] byteArray;
    using (MemoryStream stream = new MemoryStream())
    {
        bitmap.Save(stream, System.Drawing.Imaging.ImageFormat.Bmp);
        stream.Close();

        byteArray = stream.ToArray();
    }
    return byteArray;
}

Answer 4

Before use ConvertFrom save your bitmap to MemoryStream

Bitmap canvas = new Bitmap(secScreen.Bounds.Width, secScreen.Bounds.Height);
Graphics g = Graphics.FromImage(canvas);
g.Clear(System.Drawing.Color.Yellow);

MemoryStream stream = new MemoryStream ();
canvas.Save(stream, System.Drawing.Imaging.ImageFormat.Png);
ImageSource isrg = (ImageSource)new ImageSourceConverter().ConvertFrom(stream);

Answer 5

尝试将coDrivr4.Properties.Resources.Music.GetHbitmap()的返回值放入临时变量中，看看它是否为空 - 这可能是您的null来自的地方。