Regarding INotifyPropertyChanged

i never work wuth INotifyPropertyChanged. i was reading ar开发者_JAVA技巧ticle and from there i found code related with INotifyPropertyChanged.

public class ContactModel : INotifyPropertyChanged
{
    private string _firstName;

    public string FirstName
    {
        get { return _firstName; }
        set
        {
            _firstName = value;
            RaisePropertyChanged("FirstName");
            RaisePropertyChanged("FullName");
        }
    }

    private string _lastName;

    public string LastName
    {
        get { return _lastName; }
        set
        {
            _lastName = value;
            RaisePropertyChanged("LastName");
            RaisePropertyChanged("FullName");
        }
    }

    public string FullName
    {
        get { return string.Format("{0} {1}", FirstName, LastName); }
    }



    protected void RaisePropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public override bool Equals(object obj)
    {
        return obj is ContactModel && ((ContactModel) obj).FullName.Equals(FullName);
    }

    public override int GetHashCode()
    {
        return FullName.GetHashCode();
    }
}

from the above code i found RaisePropertyChanged("FirstName"); is always called from property setter. why RaisePropertyChanged is required to call. i search google for good explaination but i did not found any good link. so please if someone explain why RaisePropertyChanged need to call from setter.

thanks

Because WPF registers to the PropertyChanged event and this will make the binding work, i.e. you change the property and textbox text changes.

Also the event raising pattern is a standard one: Event is raised through a protected method so that the subclasses can turn it off/or change the behaviour.

I actually have a bit more on my view models that verify the name - originally by Josh Smith:

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {

        VerifyPropertyName(propertyName);

        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    protected void OnPropertyChanged(object sender, string propertyName)
    {
        PropertyChanged(sender, new PropertyChangedEventArgs(propertyName));
    }

    public void VerifyPropertyName(string propertyName)
    {

        if (TypeDescriptor.GetProperties(this)[propertyName] == null)
        {
            throw new Exception("Invalid property name: " + propertyName);
        }
    }

You should check inside the property setter if the property actually changes, then by rasing the event you can notify that your property has changed:

        set
        {
            if (lastname != value)
            {
               _lastName = value;
               RaisePropertyChanged("LastName");
               RaisePropertyChanged("FullName");
            }
        }

Any class that has subscribed to the PropertyChanged event, will then be notified that the property has changed, so they can update their bindings.

This is so all subscribing recipients get a message stating that the property has changed, therefore they should update their values accordingly. For example, a grid will change text.

The reason they've updated the FullName property as well, is because the First/Last name properties directly affect the FullName of the person, therefore bindings should reflect these values.