[mono-android] Not catching null reference - why?

[Joel Low]

Isn't the normal (= .NET) behaviour to throw an InvalidCastException in this
case?

 

Regards,

Joel

 

From: monodroid-bounces at lists.ximian.com
[mailto:monodroid-bounces at lists.ximian.com] On Behalf Of Sayed Arian
Kooshesh
Sent: Thursday, 21 June, 2012 6:56 PM
To: Discussions related to Mono for Android
Subject: Re: [mono-android] Not catching null reference - why?

 


correct syntax is:
if( (reference.Target as Bitmap) ==null)





On Thu, Jun 21, 2012 at 2:42 AM, bjarke <jbp at itai.dk> wrote:

Hey guys

I have a list of bitmaps with weak references however sometimes the bitmap
is null. This is okay and as expected however my issue is that it does not
work doing a check against null. This is my method;

 public static Bitmap DecodeFile(string _path)
       {
           WeakReference reference;
           var options = new BitmapFactory.Options {InPreferredConfig =
Bitmap.Config.Rgb565};
           Bitmap image=null;
           //refs is a dictionary of Dictionary<string, WeakReference>
           if (refs.TryGetValue(_path, out reference))
           {
                   if (reference.IsAlive)
                   {
                       image = (Bitmap)reference.Target;

                       if (image==null)
                       {
                       // image has been garbage collected
                       // remove reference from cache
                           refs.Remove(_path);
                       }
                       else
                       {

                           return image;
                       }


                   }
                   else
                   {
                       // image has been garbage collected
                       // remove reference from cache
                       refs.Remove(_path);
                   }

               }
           image = BitmapFactory.DecodeFile(_path, options);
           reference = new WeakReference(image);
           refs.Add(_path, reference);
           return image;
       }

The check if(image==null) is false even though it is null. If I do a
image.Equals(null) I get a nullpointer exception instead. So right now I
catch the exception instead and handle it - however I really do not like
that approach.

Any suggestion is well recieved :)

Regards Bjarke

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