What is the easiest way to get the property value from a passed lambda expression in an extension method for HtmlHelper?
Solution 1
Try like this:
public static MvcHtmlString Try<TModel, TProperty>(
this HtmlHelper<TModel> htmlHelper,
Expression<Func<TModel, TProperty>> expression
)
{
var builder = new TagBuilder("textarea");
builder.AddCssClass("ckeditor");
builder.MergeAttribute("cols", "80");
builder.MergeAttribute("name", "editor1");
builder.MergeAttribute("id", expression.Name); // not sure about the id - verify
var value = ModelMetadata.FromLambdaExpression(
expression, htmlHelper.ViewData
).Model;
builder.SetInnerText(value.ToString());
return MvcHtmlString.Create(builder.ToString());
}
Solution 2
ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
Object value = metadata.Model;
String name = metadata.PropertyName;
Solution 3
I Know this is an old thread but just in case if someone is looking for it, the way to generate id / name attribute is also:
System.Web.Mvc.ExpressionHelper.GetExpressionText(expression);
I'm using this in my extensions and never had any issues with it. It also works great with nested properties.
Solution 4
Simplest way is to wrap it all up in an extension method:
public static class ExtensionMethods
{
public static object Value<TModel, TProperty>(this Expression<Func<TModel, TProperty>> expression, ViewDataDictionary<TModel> viewData)
{
return ModelMetadata.FromLambdaExpression(expression, viewData).Model;
}
}
So the calling syntax is:
expression.Value(htmlHelper.ViewData)
Solution 5
ASP.NET MVC 3 Futures includes a helper for that.
Andrew Siemer
I am currently the Director of Engineering at Volusion, author of several technical and soft skill books, father of 6, and a big friendly guy. I love to ride horses, play with my kids, learn new stuff, teach new stuff, and have fun with life. Moved to Texas in 2010 and stated a sustainable farm where we raise vegetables, egg laying hens, meat birds, and pigs. Books: ASP.NET 3.5 Social Networking ASP.NET MVC Cookbook ASP.NET 4 Social Networking Programmer's Dream Career Sites: LostTechies.com/AndrewSiemer LinkedIn Friendly Pastures Twitter Facebook AndrewSiemer.com
Updated on July 09, 2022Comments
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Andrew Siemer almost 2 years
I am writing a dirty little extension method for HtmlHelper so that I can say something like HtmlHelper.WysiwygFor(lambda) and display the CKEditor.
I have this working currently but it seems a bit more cumbersome than I would prefer. I am hoping that there is a more straight forward way of doing this.
Here is what I have so far.
public static MvcHtmlString WysiwygFor<TModel, TProperty>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TProperty>> expression) { return MvcHtmlString.Create(string.Concat("<textarea class=\"ckeditor\" cols=\"80\" id=\"", expression.MemberName(), "\" name=\"editor1\" rows=\"10\">", GetValue(helper, expression), "</textarea>")); } private static string GetValue<TModel, TProperty>(HtmlHelper<TModel> helper, Expression<Func<TModel, TProperty>> expression) { MemberExpression body = (MemberExpression)expression.Body; string propertyName = body.Member.Name; TModel model = helper.ViewData.Model; string value = typeof(TModel).GetProperty(propertyName).GetValue(model, null).ToString(); return value; } private static string MemberName<T, V>(this Expression<Func<T, V>> expression) { var memberExpression = expression.Body as MemberExpression; if (memberExpression == null) throw new InvalidOperationException("Expression must be a member expression"); return memberExpression.Member.Name; }
Thanks!
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Andrew Siemer almost 14 yearsI was mostly interested in this line from the above - var value = ModelMetadata.FromLambdaExpression( expression, htmlHelper.ViewData ).Model; which worked great! I did find that your expression.Name returns null. I swapped that to point to my MemberName method to get that working for the ID. Also, I found that there is a TagBuilder.GenerateId() for adding the ID attribute. Thanks. I will be sure to mention you in my upcoming book (ASP.NET MVC Cookbook - groups.google.com/group/aspnet-mvc-2-cookbook-review)
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bjan almost 12 yearsThis will get the name of the Property but not its Value
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Carlos Miguel Colanta almost 8 yearsHey darin, can you please explain to me this line?
var value = ModelMetadata.FromLambdaExpression( expression, htmlHelper.ViewData ).Model;
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DaEagle over 7 yearsThis is working for me and correctly gets the property name via PropertyName where expression.Name returns null. Edit to add - I'm running MVC5 in case that matters