c# - Error handling for Tasks inside Task.WhenAll -

i'm trying create web-scraper queries lot of urls in parallel , waits responses using task.whenall(). if 1 of tasks unsuccessful, whenall fails. expecting many of tasks return 404 , wish handle or ignore those. example:

string urls = enumerable.range(1, 1000).select(i => "https://somewebsite.com/" + i)); list<task<string>> tasks = new list<task<string>>(); foreach (string url in urls) {     tasks.add(task.run(() => {         try         {             return (new httpclient()).getstringasync(url);         }         catch (httprequestexception)         {             return task.fromresult<string>("");         }     })); } var responsestrings = await task.whenall(tasks); 

this never hits catch statement, , whenall fails @ first 404. how can whenall ignore exceptions , return tasks completed successfully? better yet, done somewhere in code below?

var tasks = enumerable.range(1, 1000).select(i => (new httpclient()).getstringasync("https://somewebsite.com/" + i)))); var responsestrings = await task.whenall(tasks); 

thanks help.

you need use await observe exception:

var tasks = enumerable.range(1, 1000).select(i => trygetstringasync("https://somewebsite.com/" + i)); var responsestrings = await task.whenall(tasks); var validresponses = responsestrings.where(x => x != null);  private async task trygetstringasync(string url) {   try   {     return await httpclient.getstringasync(url);   }   catch (httprequestexception)   {     return null;   } }