Chapter88:INotifyPropertyChanged interface

Section88.1:ImplementingINotifyPropertyChangedinC#6

TheimplementationofINotifyPropertyChangecanbeerror-prone,astheinterfacerequiresspecifyingproperty nameasastring.Inordertomaketheimplementationmorerobust,anattributeCallerMemberNamecanbeused.

classC:INotifyPropertyChanged

{

//backingfield

intoffset;

//property

publicintOffset

{

get

{

returnoffset;

}

set

{

if(offset==value) return;

offset=value;

RaisePropertyChanged();

}

}

//helpermethodforraisingPropertyChangedevent

voidRaisePropertyChanged([CallerMemberName]stringpropertyName=null)=>PropertyChanged?.Invoke(this,newPropertyChangedEventArgs(propertyName));

//interfaceimplemetation

publiceventPropertyChangedEventHandlerPropertyChanged;

}

IfyouhaveseveralclassesimplementingINotifyPropertyChanged,youmayfinditusefultorefactoroutthe interfaceimplementationandthehelpermethodtothecommonbaseclass:

classNotifyPropertyChangedImpl:INotifyPropertyChanged

{

protectedvoidRaisePropertyChanged([CallerMemberName]stringpropertyName=null)=>PropertyChanged?.Invoke(this,newPropertyChangedEventArgs(propertyName));

//interfaceimplemetation

publiceventPropertyChangedEventHandlerPropertyChanged;

}

classC:NotifyPropertyChangedImpl

{

intoffset;

publicintOffset

{

get{returnoffset;}

set{if(offset!=value){offset=value;RaisePropertyChanged();}}

}

}

Section88.2:INotifyPropertyChangedWithGenericSet Method

TheNotifyPropertyChangedBaseclassbelowdefinesagenericSetmethodthatcanbecalledfromanyderived type.

publicclassNotifyPropertyChangedBase:INotifyPropertyChanged

{

protectedvoidRaisePropertyChanged([CallerMemberName]stringpropertyName=null)=>PropertyChanged?.Invoke(this,newPropertyChangedEventArgs(propertyName));

publiceventPropertyChangedEventHandlerPropertyChanged;

publicvirtualboolSet<T>(refTfield,Tvalue,[CallerMemberName]stringpropertyName=null)

{

if(Equals(field,value)) return

false;

storage=value;

RaisePropertyChanged(propertyName);

returntrue;

}

}

TousethisgenericSetmethod,yousimplyneedtocreateaclassthatderivesfromNotifyPropertyChangedBase.

publicclassSomeViewModel:NotifyPropertyChangedBase

{

privatestring_foo;

privateint_bar;

publicstringFoo

{

get{return_foo;}

set{Set(ref_foo,value);}

}

publicintBar

{

get{return_bar;}

set{Set(ref_bar,value);}

}

}

Asshownabove,youcancallSet(ref_fieldName,value);inaproperty’ssetteranditwillautomaticallyraisea PropertyChangedeventifitisneeded.

You canthen registerto thePropertyChanged eventfrom anotherclass thatneeds tohandle propertychanges.

publicclassSomeListener

{

publicSomeListener()

{

_vm=newSomeViewModel();

_vm.PropertyChanged+=OnViewModelPropertyChanged;

}

privatevoidOnViewModelPropertyChanged(objectsender,PropertyChangedEventArgse)

{

Console.WriteLine($”Property{e.PropertyName}waschanged.”);

}

privatereadonlySomeViewModel_vm;

}