Dispatcher BeginInvoke Syntax

问题

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.

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

Thanks in advance for any enlightenment!

回答1:

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);
    }));
}

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

回答2:

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);
    }));
}

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

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

回答3:

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

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

来源：https://stackoverflow.com/questions/3760777/dispatcher-begininvoke-syntax

标签

.net

multithreading

wcf-data-services