BindableBase

• May 05, 2018
• 4 minutes to read

The BindableBase class implements the INotifyPropertyChanged interface and provides capabilities for easy implementation of bindable properties with the GetProperty and SetProperty methods.

C#

public class ViewModel : BindableBase {
        public string FirstName {
            get { return GetProperty(() => FirstName); }
            set { SetProperty(() => FirstName, value); }
        }
    }

VB.NET

Public Class ViewModel
    Inherits BindableBase
    Public Property FirstName As String
        Get
            Return GetProperty(Function() FirstName)
        End Get
        Set(value As String)
            SetProperty(Function() FirstName, value)
        End Set
    End Property
End Class

The first parameter of the GetProperty and SetProperty methods is a lamda-expression that returns the property used for identifying the target property name (property names are internally obtained with the BindableBase.GetPropertyName<T> static method).

Property values are stored in an internal Dictionary (the GetProperty method uses this dictionary to get a property value based on the property name, the SetProperty method stores a property value using the property name as a key). This approach simplifies code, and allows code checking during compilation and renaming properties with standard Visual Studio refactoring capabilities.

The SetProperty method returns True or False values that indicate whether or not a property has been successfully changed (if you set the same value to the property, the SetProperty method returns False and changing notifications are not sent). Some SetProperty method overloads also take a callback method as a parameter. This callback is invoked after the field has been changed.

C#

public class ViewModel : BindableBase {
        public string FirstName {
            get { return GetProperty(() => FirstName); }
            set { SetProperty(() => FirstName, value, OnFirstNameChanged); }
        }
        void OnFirstNameChanged() {
            //...
        }
    }

VB.NET

Public Class ViewModel
    Inherits BindableBase
    Public Property FirstName As String
        Get
            Return GetProperty(Function() FirstName)
        End Get
        Set(value As String)
            SetProperty(Function() FirstName, value, AddressOf OnFirstNameChanged)
        End Set
    End Property
    Sub OnFirstNameChanged()
        '...
    End Sub
End Class

If you need to manually raise the INotifyPropertyChanged.PropertyChanged event for a specific property, use the RaisePropertyChanged/RaisePropertiesChanged method.

C#

public class ViewModel : BindableBase {
        public string FullName {
            get { return string.Format("{0} {1}", FirstName, LastName); }
        }
        public string FirstName {
            get { return GetProperty(() => FirstName); }
            set { SetProperty(() => FirstName, value, OnFirstNameChanged); }
        }
        public string LastName {
            get { return GetProperty(() => LastName); }
            set {
                if(SetProperty(() => LastName, value))
                    RaisePropertyChanged(() => FullName);
            }
        }
        void OnFirstNameChanged() {
            RaisePropertyChanged(() => FullName);
        }
    }

VB.NET

Public Class ViewModel
    Inherits BindableBase
    Public ReadOnly Property FullName As String
        Get
            Return String.Format("{0} {1}", FirstName, LastName)
        End Get
    End Property
    Public Property FirstName As String
        Get
            Return GetProperty(Function() FirstName)
        End Get
        Set(value As String)
            SetProperty(Function() FirstName, value, AddressOf OnFirstNameChanged)
        End Set
    End Property
    Public Property LastName As String
        Get
            Return GetProperty(Function() LastName)
        End Get
        Set(value As String)
            If SetProperty(Function() LastName, value) Then
                RaisePropertyChanged(Function() FullName)
            End If
        End Set
    End Property
    Sub OnFirstNameChanged()
        RaisePropertyChanged(Function() FullName)
    End Sub
End Class

In rare cases, application performance can deteriorate when a property is frequently updated (due to the calculation of property names from lambda-expressions and the accessing of properties from the Dictionary storage). To accommodate these scenarios, use storage variables for properties and calculate property names once from the static constructor using the BindableBase.GetPropertyName<T> method.

C#

public class ViewModel : BindableBase {
        static string Property1Name;
        static ViewModel() {
            Property1Name = BindableBase.GetPropertyName(() => new ViewModel().Property1);
        }

        string property1;
        public string Property1 {
            get { return property1; }
            set { SetProperty(ref property1, value, Property1Name); }
        }
    }

VB.NET

Public Class ViewModel
    Inherits BindableBase
    Shared Property1Name As String
    Shared Sub New()
        Property1Name = BindableBase.GetPropertyName(Function() New ViewModel().Property1)
    End Sub

    Dim _Property1 As String
    Public Property Property1 As String
        Get
            Return _Property1
        End Get
        Set(value As String)
            SetProperty(_Property1, value, Property1Name)
        End Set
    End Property
End Class