The type arguments cannot be inferred from the usage Try specifying the type arguments explicitly

Question

Could someone please clarify something for me  In my ASP NET MVC 2 app  I ve got a BaseViewModel class which includes the following method    public virtual IDictionary lt string  object gt  GetHtmlAttributes lt TModel  TProperty gt                           Expression lt Func lt TModel  TProperty gt  gt  propertyExpression        return new Dictionary lt string  object gt         The idea being that each child viewmodel can override this method and provide a suitable set of html attributes  based on some logic  to be rendered in the view    lt    Html TextBoxFor model   gt  model MyProperty  Model GetHtmlAttributes                                                   model   gt  model MyProperty     gt    However when used as in the line above  I get a compilation error when I hit the view      The type arguments for method     BaseViewModel GetHtmlAttributes lt TModel TProperty gt  Expression lt System Func lt TModel TProperty gt    cannot be inferred from the usage  Try specifying the type arguments explicitly    I have to do the following    lt    Html TextBoxFor model   gt  model MyProperty  Model GetHtmlAttributes                               lt ChildModel  string gt  model   gt  model MyProperty     gt    I m just looking for some clarity as to how it tries to infer the type  it has no problem doing so in the HtmlHelper TextBoxFor extension method    Is it because HtmlHelper in the view will automatically be for the same type as is specified in the ViewUserControl at the top of the page  whereas my code can be for any type inheriting from BaseViewModel  Is is possible to write this in such a way that it can infer my model property types

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I had this same problem  my solution   In the web config file     lt compilation debug  true gt  had to be changed to  lt compilation debug  true  targetFramework  4 0  gt

User · Answer

In your example  the compiler has no way of knowing what type should TModel be  You could do something close to what you are probably trying to do with an extension method   static class ModelExtensions      public static IDictionary lt string  object gt  GetHtmlAttributes lt TModel  TProperty gt         this TModel model  Expression lt Func lt TModel  TProperty gt  gt  propertyExpression              return new Dictionary lt string  object gt              But you wouldn t be able to have anything similar to virtual  I think   EDIT   Actually  you can do virtual  using self-referential generics   class ModelBase lt TModel gt        public virtual IDictionary lt string  object gt  GetHtmlAttributes lt TProperty gt           Expression lt Func lt TModel  TProperty gt  gt  propertyExpression                return new Dictionary lt string  object gt              class FooModel   ModelBase lt FooModel gt        public override IDictionary lt string  object gt  GetHtmlAttributes lt TProperty gt           Expression lt Func lt FooModel  TProperty gt  gt  propertyExpression                return new Dictionary lt string  object gt       foo    bar

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I was actually searching for a similar error and Google sent me here to this question  The error was      The type arguments for method    IModelExpressionProvider CreateModelExpression ViewDataDictionary  Expression      cannot be inferred from the usage   I spent maybe 15 minutes trying to figure it out  It was happening inside a Razor  cshtml view file  I had to comment portions of the view code to get to where it was barking since the compiler didn t help much    lt div class  form-group col-2  gt       lt label asp-for  Organization Zip  gt  lt  label gt       lt input asp-for  Organization Zip  class  form-control  gt       lt span asp-validation-for  Zip  class  color-type-alert  gt  lt  span gt   lt  div gt    Can you spot it  Yeah    I re-checked it maybe twice and didn t get it at first   See that the ViewModel s property is just Zip when it should be Organization Zip  That was it   So re-check your view source code     -

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This error is also related with a cache issue   I had the same problem and it was solved just cleaning and building the solution again

User · Answer

You are referring to the type rather than the instance   Make  Model  lowercase in the example in your second and fourth code samples   Model GetHtmlAttributes   should be  model GetHtmlAttributes

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In case it helps  I ve ran into this problem when passing null into a parameter for a generic TValue  to get around this you have to cast your null values    string null   int null   etc

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C  compiler have only lambda  arg   gt  arg MyProperty   for infer type of arg TModel  an type of arg MyProperty TProperty   It s impossible

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I know this question already has an accepted answer  but for me  a  NET beginner  there was a simple solution to what I was doing wrong and I thought I d share    I had been doing this    Html HiddenFor Model Foo Bar ID    What worked for me was changing to this    Html HiddenFor m   gt  m Foo Bar ID     where  m  is an arbitrary string to represent the model object

[c#] The type arguments cannot be inferred from the usage. Try specifying the type arguments explicitly

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