Avoid using LoadAsync() method of PictureBox control

Steps to reproduce:

1. Create a new WinForms Core App.
2. Add the following Code to the Form’s constructor.

public Form1()
        {
            InitializeComponent();
            System.Windows.Forms.PictureBox pb = new PictureBox();
            pb.ImageLocation = @"\\winformssrvvm01\BAQAFiles\v-mikou\OGF Doc\picture\myLargeImage1.bmp";
            pb.LoadAsync();
        }

1. Run the app.

Expected Result: LoadAsync should be executed. (NOTE: Although LoadAsync implies this, the method does not return Task but void, so the usage here is correct with regards to async/await.)

Actual Result: An exception pops up, please see following screenshot and exception log.

Exception log:

System.PlatformNotSupportedException
  HResult=0x80131539
  Message=Operation is not supported on this platform.
  Source=System.Private.CoreLib
  StackTrace:
   at System.Threading.WaitCallback.BeginInvoke(Object state, AsyncCallback callback, Object object)
   at System.Windows.Forms.PictureBox.LoadAsync()
   at XpictureIssue.Form1..ctor() in C:\Users\v-zheshi\source\winforms\XpictureIssue\Form1.cs:line 20
   at XpictureIssue.Program.Main() in C:\Users\v-zheshi\source\winforms\XpictureIssue\Program.cs:line 19

[ericstj]

Just to confirm, I believe this is intentional per https://github.com/dotnet/corefx/issues/5940#issuecomment-182107557 /cc @jkotas. You’ll need to make a fix to WinForms here to avoid this API. The comment here may not even apply any more on Core so perhaps you can just call BeginGetResponse https://github.com/dotnet/winforms/blob/408a31db5c58be99eff71ed94dfae6fda49364e0/src/System.Windows.Forms/src/System/Windows/Forms/PictureBox.cs#L671-L674 Alternatively just use the Task infrastructure to run the code on a background thread.

In addition: What do folks think about making this method Obsolete, and come up with a new one which does keep what its promising (namely returning Task and not void)?

We had similar goals back in .NETCore1.0 but dialed it back. In most cases it’s not worth breaking someone over just having a newer API. There should be some really good reason to force a dev to think about the change. “New” is not a good enough reason. Thus we still have all the old event-based and APM based API next to task based API.

It’s a reasonable goal to plumb task-based async API through WinForms, but that should be done in a wave impacting all async winforms APIs. That way you aren’t forcing people to learn two different async programming models. I can imagine that being a pretty huge task given that WinForms relies heavily on the event-based model.

[KlausLoeffelmann]

In addition: What do folks think about making this method Obsolete, and come up with a new one which does keep what its promising (namely returning Task and not void)?