Skip to main content

Using IDataErrorInfo for Validation

I read an article on CodeProject titled Total View Validation where the author complains that IDataErrorInfo is inadequate for WPF validation.  The assumption he makes is that all the validation code needs to go into the IDataErrorInfo.this[string] property as such:

[csharp]
public string this[string name]
{
get
{
string result = null;
if (name == "Age")
{
if (this.age < 0 || this.age > 150)
{
result = "Age must not be less than 0 or greater than 150.";
}
}
return result;
}
}
[/csharp]

This should not be the way that IDataErrorInfo is used as it puts business logic in the model, as the author points out. His solution though was to create another mechanism to notifiy the user of validation errors and to not use IDataErrorInfo at all.

A solution I would propose though would be to follow how DataTables and DataTables use IDataErrorInfo by implementing methods to set and clear the objects error information:

[csharp]
public class SomeClass : IDataErrorInfo
{

public string Name { get; set; }

public string Age { get; set; }

#region Data Error Info

private Dictionary<string, string> _propertyErrors;

private void InitDataErrorInfo()
{
var properties = this.GetType().GetProperties();

_propertyErrors = new Dictionary<string, string>
{
// This will act as an overall error message for the entire object.
{this.GetHashCode().ToString(CultureInfo.InvariantCulture), string.Empty}
};


foreach (var propertyInfo in properties)
_propertyErrors.Add(propertyInfo.Name, string.Empty);
}

public void ClearDataErrorInfo()
{
foreach (var property in _propertyErrors.Keys)
_propertyErrors[property] = string.Empty;
}

public void ClearDataErrorInfo(string propertyName)
{
AssertThisHasPropertyWithName(propertyName);
_propertyErrors[propertyName] = string.Empty;
}

public void SetError(string error)
{
SetError(this.GetHashCode().ToString(CultureInfo.InvariantCulture), error);
}

public void SetError(string propertyName, string error)
{
AssertThisHasPropertyWithName(propertyName);
_propertyErrors[propertyName] = string.Format("{0}{1}{2}", _propertyErrors[propertyName]
, Environment.NewLine, error);
}

public string this[string propertyName]
{
get
{
AssertThisHasPropertyWithName(propertyName);
return _propertyErrors[propertyName];
}

}

public string Error
{
get
{
var errors = new StringBuilder();
foreach (
var propertyError in
_propertyErrors.Where(propertyError => !string.IsNullOrEmpty(propertyError.Value)))
errors.AppendLine(propertyError.Value);

return errors.ToString().Trim();
}
}

protected void AssertThisHasPropertyWithName(string propertyName)
{
if (!_propertyErrors.ContainsKey(propertyName))
{
throw new ArgumentException(string.Format("No property named {0} on {1}."
, propertyName, this.GetType().FullName));
}
}

#endregion
}
[/csharp]

Note that there is no validation here, only reporting if the object has errors. Using this takes advantage of the already existing validation notification built into WPF as well as WinForms.

Comments

Popular posts from this blog

Json for jqGrid from ASP.Net MVC

jqGrid takes a specific format for its json (taken from jqGrid documentation): [js]{ total: "xxx",page: "yyy", records: "zzz", rows : [ {id:"1", cell:["cell11", "cell12", "cell13"]}, {id:"2", cell:["cell21", "cell22", "cell23"]}, ... ]}[/js] The tags mean the following: total - Total number of Pages. page - Current page Index. records - Total number of records in the rows group. rows - An array with the data plus an identifier. id - The unique row identifier, needs to be an int from what I have found. cell - An array of the data for the grid. The ASP.Net MVC framework has the JsonResult response type which we can use to populate the jqGrid. As an example I created a Person model and a method to return some data: [csharp] public class Person { public int ID { get; set; } public string Name { get; set; } public DateTime Birthday { get; set; } } public I

Changing Typed DataSet Connection String

I was working on a WinForm app that connected to a MS Access database. Yeah, Access sucks but I didn't have a choice in the matter. The app itself is used to import a bunch of CSV files into the Access database. It is more of a utility program and it has going through several variations, from being a simple hand driven command line tool to being GUI driven. The command line version was all hand controlled. I had to go in and update configuration files to point to the CSV files and the MDB database. That got old fast so I decided to make a GUI version that would allow me to pick the MDB file and each of the CSV files to import. Picking and using the CSV files was easy, it was changing the connection string for the MDB that proved to be the hardest. I am using strongly typed datasets in VS2005. If you have ever worked with them you find out soon that the connection string gets saved with the project in the app.config file, even if it is a seperate DAL dll project. My guess is

Remote Controlled RoboTank

This is my version of the ever popular to build RoboTank. It uses an Arduino Mega 2560 with the AdaFruit motor shield and an XBee S1 to communicate to the DFRobot Gamepad. The sketch for the RoboTank makes use of the AFMotor.h to drive the motors and includes a serial parser to read and process the commands coming from the Gamepad. Robotank-Sketch.zip DFRobot Wireless Joystick