CODEWITHSUNDEEP
c#.netmultithreadingwcf-data-services
Jon Archway
Jon Archway

Reputation: 4892

Dispatcher BeginInvoke Syntax

I have been trying to follow some WCF Data Services examples and have the following code:

private void OnSaveCompleted(IAsyncResult result)
    {
        Dispatcher.BeginInvoke(() =>
        {
            context.EndSaveChanges(result);
        });
    }

Which is called by the following:

this.context.BeginSaveChanges(SaveChangesOptions.Batch, this.OnSaveCompleted, null);

Now I am getting a little confused here. Firstly, the first bit of code is showing a syntax error of

Argument type lambda expression is not assignable to parameter type System.Delegate

So instead of blindly trying to follow the example code, I tried to understand what was going on here. Unfortunately, I am struggling to understand the error plus what is actually happening. Can anyone explain?

I feel a bit stupid as I am sure this is easy.

Upvotes: 62

Views: 87187

Answers (3)

Alon Amsalem
Alon Amsalem

Reputation: 306

If your method does not require parameters, this is the shortest version I've found

Application.Current.Dispatcher.BeginInvoke((Action)MethodName);

Upvotes: 6

CoperNick
CoperNick

Reputation: 2533

Answer by Jon Skeet is very good but there are other possibilities. I prefer "begin invoke new action" which is easy to read and to remember for me.

private void OnSaveCompleted(IAsyncResult result)
{       
    Dispatcher.BeginInvoke(new Action(() =>
    {
        context.EndSaveChanges(result);
    }));
}

or

private void OnSaveCompleted(IAsyncResult result)
{       
    Dispatcher.BeginInvoke(new Action(delegate
    {
        context.EndSaveChanges(result);
    }));
}

or

private void OnSaveCompleted(IAsyncResult result)
{       
    Dispatcher.BeginInvoke(new Action(() => context.EndSaveChanges(result)));
}

Upvotes: 17

Jon Skeet
Jon Skeet

Reputation: 1503140

The problem is that the compiler doesn't know what kind of delegate you're trying to convert the lambda expression to. You can fix that either with a cast, or a separate variable:

private void OnSaveCompleted(IAsyncResult result)
{        
    Dispatcher.BeginInvoke((Action) (() =>
    {
        context.EndSaveChanges(result);
    }));
}

or

private void OnSaveCompleted(IAsyncResult result)
{
    Action action = () =>
    {
        context.EndSaveChanges(result);
    };
    Dispatcher.BeginInvoke(action);
}

Upvotes: 119

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