C# | C# 5.0 Features

Async & Await

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();
    //Assign the event handler
    web.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
    //Download the file async
    web.DownloadFileAsync(new Uri(uri), DownloadLocation);
    //Notice how there is no complete event, instead we're using techniques from the first example
}
private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e){
    int i = 0;
    i++;
    doSomething();
}
private void doProcess(){
    //Wait for the download to finish
    await DownloadAndUpdateAsync(new Uri("http://example.com/file"))
    doSomething();
}

Caller Information Attributes

C.I.A.s are intended as a simple way of getting attributes from whatever is calling the targeted method. There is really only 1 way to use them and there are only 3 attributes.

Example:

//This is the "calling method": the method that is calling the target method
public void doProcess()
{
    GetMessageCallerAttributes("Show my attributes.");
}
//This is the target method
//There are only 3 caller attributes
public void GetMessageCallerAttributes(string message,
    //gets the name of what is calling this method
    [System.Runtime.CompilerServices.CallerMemberName] string memberName = "",
    //gets the path of the file in which the "calling method" is in
    [System.Runtime.CompilerServices.CallerFilePath] string sourceFilePath = "",
    //gets the line number of the "calling method"
    [System.Runtime.CompilerServices.CallerLineNumber] int sourceLineNumber = 0)
{
    //Writes lines of all the attributes
    System.Diagnostics.Trace.WriteLine("Message: " + message);
    System.Diagnostics.Trace.WriteLine("Member: " + memberName);
    System.Diagnostics.Trace.WriteLine("Source File Path: " + sourceFilePath);
    System.Diagnostics.Trace.WriteLine("Line Number: " + sourceLineNumber);
}

Example Output:

//Message: Show my attributes.
//Member: doProcess
//Source File Path: c:\Path\To\The\File
//Line Number: 13

Syntax

****Async & Await****

public **Task** MyTask**Async**(){ doSomething(); } await MyTaskAsync();

public **Task``** MyStringTask**Async**(){ return getSomeString(); } string MyString = await MyStringTaskAsync();

****Caller Information Attributes****

public void MyCallerAttributes(string MyMessage, [CallerMemberName] string MemberName = "", [CallerFilePath] string SourceFilePath = "", [CallerLineNumber] int LineNumber = 0)

Trace.WriteLine("My Message: " + MyMessage); Trace.WriteLine("Member: " + MemberName); Trace.WriteLine("Source File Path: " + SourceFilePath); Trace.WriteLine("Line Number: " + LineNumber);

Parameters

|Method/Modifier with Parameter|Details |---|---|---|---|---|---|---|---|---|--- |Type<T>|T is the return type

Remarks

C# 5.0 is coupled with Visual Studio .NET 2012