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How to improve our MVVM application using CallerMemberName

Zilele astea am descoperit cateva noi atribute in .NET 4.5 care ne sunt f. utile intr-o aplicatie MVVM si nu numai.
In namespace-ul System.Runtime.CompilerServices o sa gasim cateva atribute noi care ne permite sa accesam informatii despre cine a apelat metoda, la ce linie si locatia fisierului cs. Aceste informatii ne pot ajuta cand vrem sa scriem in log anumite date. In loc sa transmitem ca si parametru de fiecare data cine face apelul, putem sa specificam prin intermediul acestor atribute. In exemplul de mai jos, o logam cine a apelat metoda, locatia fisierului care a apelato si numarul linii de cod de unde s-a facut apelul:
public void WriteLog(
[CallerMemberName] string memberName = "",
[CallerFilePath] string filePath = "",
[CallerLineNumber] int lineNumber = 0)
{
Debug.WriteLine(String.Format("{0}-{1}: {2} ", filePath, lineNumber, memberName));
}
...
WriteLog(); // apel metoda
Orice metoda care o sa apeleze aceasta metoda, nu o sa trebuiasca sa specifice nici un parametru. Fiecare parametru o sa fie rezolvat la runtime. Este obligatoriu ca acest parametrii sa aibe o valoare default.
In functie de locatia de unde apelata metoda noastra, valoarea lui CallerMemberName poate sa difere. De exemplu daca metoda noastra ar fi apelata din constructor atunci memberName ar avea valoarea ".ctor".
Mai multe informatii despre aceste 3 atribute puteti sa gasiti aici.
Acuma sa ne uitam peste un caz unde ne este de folos atributul CallerMemberName. Intr-o aplicatie MVVM, avem nevoie sa notificam ce pro pietate s-a modificat. Acest lucru se facea pana acuma in felul urmator:
public class Car : INotifyPropertyChanged
{
private string _model;
public string Model
{
get
{
return _model;
}
set
{
_model = value;
NotifyPropertyChanged("Model");
}
}

public void NotifyPropertyChanged(string property = null)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
Acuma ne putem folosii de atributul CallerMemberName pentru a specifica ce propietate s-a schimbat. Prin intermediul acestui atribut nu mai este nevoie sa specificam de fiecare data ce propietate si-a schimbat valoarea. Codul de mai sus ar atata in felul urmator:
public class Car : INotifyPropertyChanged
{
private string _model;
public string Model
{
get
{
return _model;
}
set
{
_model = value;
NotifyPropertyChanged();
}
}

public void NotifyPropertyChanged([CallerMemberName] string property = null)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
In cazul in care facem o redenumire la o propietate sau la o metoda nu o sa mai fie nevoie sa facem update la string-urile care hardcodau numele propietatii sau a metodei.
Pe .NET 4.0 in cazul in care vreti sa obtineti numele unei metoda la runtime se poate face cu System.Reflection.MethodBase.GetCurrentMethod().Name In cazul in care apelati aceasta metoda dintr-o propietate o sa obtine valori de forma:
  • get_{numePropietate}
  • set_{numePropietate}
Enjoy!

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