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This is a very basic question. From my understanding, += can be used to concatenate two strings. I've stopped using it because there's something I'm not understanding about it.

I downloaded a code sample from Microsoft. The variable Shown is not declared as a string and is nowhere else in the program. I am aware that this is a partial class.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading.Tasks;
using System.Net;
using System.Threading;
using System.Diagnostics;

namespace DownloadAsyncProgress
	public partial class frmDownloadAsync : Form
		public frmDownloadAsync()

			Shown += async ( s, e ) => { txtResult.Text = ( await DownloadAsync() ).Replace( "\n", "\r\n" ) + "Done!"; };

		async Task<string> DownloadAsync()
			Debug.WriteLine( "\nDownloadAsync()" );

			using ( var wc = new WebClient() )
				var progress = new Progress<DownloadStringTaskAsyncExProgress>();

				progress.ProgressChanged += ( s, e ) =>
						Debug.WriteLine( "Progress: " + e.ProgressPercentage + "%" );

						progressBar.Value = e.ProgressPercentage;

						txtResult.Text += e.Text.Replace( "\n", "\r\n" );

				return await wc.DownloadStringTaskAsyncEx( @"", progress );

What I have tried:

The code works. I was expecting to see a global variable declaration, but Shown is no where else in the program.
Updated 22-Jul-18 0:26am

1 solution

For starters, C# doesn't support (or even have a concept of) global variables: everything is contained within a class. The closest it can get is a static variable that is accessed via the class name.

But ... you can't find the definition of Shown because it's not in your code - it's an Event which is part of the Form class: Form.Shown Event (System.Windows.Forms)[^]
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[no name] 22-Jul-18 7:33am    
Thank you! Can you think of what async ( s, e ) might be? Given your info, I'm a bit closer, but these constructs are new to me and I can't make them out and not sure even what to search for, in this case. I have read up on async, but my brain isn't understanding it for some reason. I just wanted to know what to search for.
OriginalGriff 22-Jul-18 7:42am    
Start here:

It's way too much to fit into a tiny textbox like this!
[no name] 22-Jul-18 8:16am    
Ok, so I take it s and e are parameters of the async method. I didn't know it accepted parameters and never saw anyone use async with parameters so wasn't sure.
OriginalGriff 22-Jul-18 8:26am    
:laugh: How else would you tell it what to process?
[no name] 22-Jul-18 8:33am    
I thought async was a keyword though. I'm completely lost, but it's alright. I'm reading this article today.

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