C# Language
C # 5.0 Caratteristiche

Sintassi

• Async e attesa

• public Task MyTask Async () {doSomething (); }

  attendo MyTaskAsync ();

• public Task <string> MyStringTask Async () {return getSomeString (); }

  string MyString = attendi MyStringTaskAsync ();

• Attributi informazioni sul chiamante

• public void MyCallerAttributes (stringa MyMessage,

  [CallerMemberName] string MemberName = "",

  [CallerFilePath] string SourceFilePath = "",

  [CallerLineNumber] int LineNumber = 0)

• Trace.WriteLine ("My Message:" + MyMessage);

  Trace.WriteLine ("Membro:" + MemberName);

  Trace.WriteLine ("Percorso file di origine:" + SourceFilePath);

  Trace.WriteLine ("Line Number:" + LineNumber);

Parametri

Osservazioni

Async e attesa

async e await sono due operatori che hanno lo scopo di migliorare le prestazioni liberando Thread e attendendo il completamento delle operazioni prima di andare avanti.

Ecco un esempio di come ottenere una stringa prima di restituire la sua lunghezza:

//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);
}

Ecco un altro esempio di download di un file e gestione di ciò che accade quando il progresso è cambiato e al termine del download (ci sono due modi per farlo):

Metodo 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!")
}

Metodo 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();
}

Attributi informazioni sul chiamante

Le CIA sono intese come un modo semplice per ottenere attributi da qualunque cosa stia chiamando il metodo mirato. C'è solo un modo per usarli e ci sono solo 3 attributi.

Esempio:

//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);
}

Esempio di output:

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