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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:
OnPropertyChanged("PropertyName")
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)
{
    OnPropertyChanged(GetProperty(expression).Name);
}
 
//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;
}
</t></func></t></t></func></t></t></func></t>
 
10/4/11 - Added a needed method to the sample code and fixed a few areas where the parameter definition got munched.

License

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

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About the Author

Jeremy Hutchinson
Software Developer Winxnet
United States United States
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Comments and Discussions

 
QuestionNice code but there is a potential performance hit PinmemberSBendBuckeye14-Feb-13 8:05 
MVVM – Lambda vs INotifyPropertyChanged vs DependencyObject
http://blog.quantumbitdesigns.com/2010/01/26/mvvm-lambda-vs-inotifypropertychanged-vs-dependencyobject/[^]
Have a great day!
 
j2associates_NO_SPAM_@yahoo.com

QuestionNice PinmemberEaverae3-Oct-11 20:46 

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