Pass lambda expression/anonymous method into BackgroundWorker

Question

Suppose I have a BackgroundWorker in my code. I want to pass anonymous function/delegate in it at start. The code bellow is what I want to do:

BackgroundWorker bw = new BackgroundWorker();
bw.DoWork += (object sender, DoWorkEventArgs e) => {
    Func<string> f = (Func<string>)e.Argument;
    f("step one");
    ...
    f("step two");
}
bw.RunWorkerAsync((string txt) => {Console.WriteLine(txt);} ); // doesn't work
// bw.RunWorkerAsync( delegate(string txt) { Console.WriteLine(txt); })); // doesn't work too

The error:

Cannot convert anonymous method to type 'object' because it is not a delegate type

Or

Cannot convert lambda expression to type 'object' because it is not a delegate type

So how can I passinto lambda expression/anonymous method into BackgroundWorker?

Here is a code in C to describe exactly what I need:

void func(char *ch)
{
    printf("%s", ch);
}

void test( void (* f)(char *) )
{
    f("blabla");
}


int main(int argc, char *argv[])
{
    test(func);
    return 0;
}

Possible duplicate of C# Pass Lambda Expression as Method Parameter — Enfyve
– Enfyve, Commented Oct 26, 2016 at 10:53
Your code has a Func<string> f type which you are calling with a string. This won't compile as f is a function which takes nothing and returns a string. You need Action<string> f. — Sean
– Sean, Commented Oct 26, 2016 at 10:53
Assign it to a variable and pass it as a parameter Action<string> obj = Console.WriteLine; bw.RunWorkerAsync(obj); Yes, you need Action<string> not Func<string> — Semuserable
– Semuserable, Commented Oct 26, 2016 at 10:55

Sean · Accepted Answer · 2016-10-26 10:56:29Z

2

You need to assign the lambda to a variable and then pass it in:

Action<string> action = (string txt) => Console.WriteLine(txt);
bw.RunWorkerAsync(action);

Note that I've used an Action<> as your code takes data and doesn't return anything. Your DoWork handler is wrong and should be like this:

bw.DoWork += (object sender, DoWorkEventArgs e) => {
    Action<string> f = (Action<string>)e.Argument;
    f("step one");
    ...
    f("step two");
}

edited Oct 26, 2016 at 10:56

answered Oct 26, 2016 at 10:39

Sean

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1 Comment

folibis Over a year ago

Thanks, @Sean that's exactly what I need. And yes, I've written Func<string> just for example to describe my target.

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