Page 175 - CSharp/C#

async and await are two operators that are intended to improve performance by freeing up Threads
and waiting for operations to complete before moving forward.

Here's an example of getting a string before returning it's length:

//This method is async because:
//1. It has async and Task or Task<T> as modifiers
//2. It ends in "Async"
async Task<int> GetStringLengthAsync(string URL){
HttpClient client = new HttpClient();
//Sends a GET request and returns the response body as a string
Task<string> getString = client.GetStringAsync(URL);
//Waits for getString to complete before returning its length
string contents = await getString;
return contents.Length;
}

private async void doProcess(){
int length = await GetStringLengthAsync("http://example.com/");
//Waits for all the above to finish before printing the number
Console.WriteLine(length);
}

Here's another example of downloading a file and handling what happens when it's progress has
changed and when the download completes (there are two ways to do this):

Method 1:

//This one using async event handlers, but not async coupled with await
private void DownloadAndUpdateAsync(string uri, string DownloadLocation){
WebClient web = new WebClient();
//Assign the event handler
web.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
web.DownloadFileCompleted += new AsyncCompletedEventHandler(FileCompleted);
//Download the file asynchronously
web.DownloadFileAsync(new Uri(uri), DownloadLocation);
}

//event called for when download progress has changed
private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e){
//example code
int i = 0;
i++;
doSomething();
}

//event called for when download has finished
private void FileCompleted(object sender, AsyncCompletedEventArgs e){
Console.WriteLine("Completed!")
}

Method 2:

//however, this one does
//Refer to first example on why this method is async
private void DownloadAndUpdateAsync(string uri, string DownloadLocation){
WebClient web = new WebClient();

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