But one question, how to display de _error in html?

Error 3 No defining declaration found for implementing declaration of partial method 'MvcScorecardEdmCSharp.Models.Measure.OnMeasureTitleChanging(string)' C:\Visual Studio 2010\Projects\MvcScorecardEdmCSharp\MvcScorecardEdmCSharp\Models\Measure.cs 9 22 MvcScorecardEdmCSharp

My code is listed below. I think it is acting like it does not realize that I have implemented the IDataError interface so it is removing the On...Changing method in the EMD class? Any ideas on what my problem is? Thanks.

using System.Collections.Generic;

using System.ComponentModel; //satisfies reference to IDataErrorInfo

namespace MvcScorecardEdmCSharp.Models

{

public partial class Measure : IDataErrorInfo

{

private Dictionary<string, string> _errors = new Dictionary<string, string>();

partial void OnMeasureTitleChanging(string value)

{

if (value.Trim().Length == 0)

_errors.Add("MeasureTitle", "MeasureTitle is required.");

}

#region IDataErrorInfo Members

public string Error

{

get

{

return string.Empty;

}

}

public string this[string columnName]

{

get

{

if (_errors.ContainsKey(columnName))

return _errors[columnName];

return string.Empty;

}

}

#endregion

}

}

i think in the tutorial, Stephen has explained your concerned issue, please look below content:

[ The DefaultModelBinder detects whether or not a class implements the IDataErrorInfo interface. If a class implements this interface then the model binder invokes the IDataErrorInfo.this indexer for each property of the class. If the indexer returns an error message then the model binder adds this error message to model state automatically.]

before the action called, it will initialize an instance automatically. During the initialization, it will invoke IDataErrorInfo.this indexer to find whether or not has errors iterative. if errors exist, the DefaultModelBinder will add these errors to ModelState. this ModelState will display in the view.