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Posted 20 Sep 2011

Make OnPropertyChanged events safe for refactoring

, 4 Oct 2011
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Use OnPropertyChanged events without Magic Strings
Here's a little trick I picked up somewhere that allows you to pass the actual property rather than the property name when raising an OnPropertyChanged event. It allows for safe refactoring of property names as well as compile time validation.

With this code, instead of this:

you can use this:
OnPropertyChanged(() => this.PropertyName)

public event PropertyChangedEventHandler PropertyChanged;
//Traditional OnPropertyChanded method
public void OnPropertyChanged(string propertyName)
    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler != null)
        handler(this, new PropertyChangedEventArgs(propertyName));
//New and improved OnPropertyChanged method
protected void OnPropertyChanged<t>(Expression<func><t>> expression)
//Helper method
public static PropertyInfo GetProperty<t>(Expression<func><t>> expression)
    PropertyInfo property = GetMember(expression) as PropertyInfo;
    if (property == null)
        throw new ArgumentException("Not a property expression", GetMember(() => expression).Name);
    return property;
//Helper method
public static MemberInfo GetMember<t>(Expression<func><t>> expression)
    if (expression == null)
        throw new ArgumentNullException(GetMember(() => expression).Name);

    return GetMemberInfo(expression as LambdaExpression);
//Helper method
public static MemberInfo GetMemberInfo(LambdaExpression lambda)
    if (lambda == null)
        throw new ArgumentNullException(GetMember(() => lambda).Name);

    MemberExpression memberExpression = null;
    if (lambda.Body.NodeType == ExpressionType.Convert)
        memberExpression = ((UnaryExpression)lambda.Body).Operand as MemberExpression;
    else if (lambda.Body.NodeType == ExpressionType.MemberAccess)
        memberExpression = lambda.Body as MemberExpression;
    else if (lambda.Body.NodeType == ExpressionType.Call)
        return ((MethodCallExpression)lambda.Body).Method;

    if (memberExpression == null)
        throw new ArgumentException("Not a member access", GetMember(() => lambda).Name);

    return memberExpression.Member;

10/4/11 - Added a needed method to the sample code and fixed a few areas where the parameter definition got munched.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Jeremy Hutchinson
Software Developer
United States United States
I develop applications using Angular, ASP.Net MVC and SQL hosted on AWS by day, and in my free time I develop apps for Windows Phone and Windows 10 as well as web apps hosted in Azure. I always try to blog about what I've learned.

I also help run the Casco Bay .Net User Group

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Comments and Discussions

QuestionNice code but there is a potential performance hit Pin
SBendBuckeye14-Feb-13 9:05
memberSBendBuckeye14-Feb-13 9:05 
QuestionNice Pin
Eaverae3-Oct-11 21:46
memberEaverae3-Oct-11 21:46 

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