Tarun Tarun - 1 month ago 12
C# Question

Enable Disable save button during Validation using IDataErrorInfo

How to disable/enable a button while doing validation using

IDataErrorInfo
?

I am using
MVVM
using GalaSoft light Framework. In my Model class I have implemented
IDataErrorInfo
to display the error messages.

public string this[string columnName]
{
get
{
Result = null;
if (columnName == "FirstName")
{
if (String.IsNullOrEmpty(FirstName))
{
Result = "Please enter first name";
}
}
else if (columnName == "LastName")
{
if (String.IsNullOrEmpty(LastName))
{
Result = "Please enter last name";
}
}

else if (columnName == "Address")
{
if (String.IsNullOrEmpty(Address))
{
Result = "Please enter Address";
}
}

else if (columnName == "City")
{
if (String.IsNullOrEmpty(City))
{
Result = "Please enter city";
}
}

else if (columnName == "State")
{
if (State == "Select")
{
Result = "Please select state";
}
}

else if (columnName == "Zip")
{
if (String.IsNullOrEmpty(Zip))
{
Result = "Please enter zip";

}
else if (Zip.Length < 6)
{
Result = "Zip's length has to be at least 6 digits!";

}
else
{
bool zipNumber = Regex.IsMatch(Zip, @"^[0-9]*$");

if (zipNumber == false)
{
Result = "Please enter only digits in zip";


}
}
}
else if (columnName == "IsValid")
{
Result = true.ToString();
}

return Result;

}
}


Screenshot: http://i.stack.imgur.com/kwEI8.jpg

How to disable/enable save button. Kindly suggest?

Thanks

Answer

The Josh Smith Way of doing this is to create the following methods in the Model:

static readonly string[] ValidatedProperties =
{
    "Foo",
    "Bar"
};

/// <summary>
/// Returns true if this object has no validation errors.
/// </summary>
public bool IsValid
{
    get
    {
        foreach (string property in ValidatedProperties)
        {

            if (GetValidationError(property) != null) // there is an error
                return false;
        }

        return true;
    }
}

private string GetValidationError(string propertyName)
{
    string error = null;

    switch (propertyName)
    {
        case "Foo":
            error = this.ValidateFoo();
            break;

        case "Bar":
            error = this.ValidateBar();
            break;

        default:
            error = null;
            throw new Exception("Unexpected property being validated on Service");
    }

    return error;
}

The ViewModel then contains a CanSave Property that reads the IsValid property on the Model:

/// <summary>
/// Checks if all parameters on the Model are valid and ready to be saved
/// </summary>
protected bool CanSave
{
    get
    {
        return modelOfThisVM.IsValid;
    }
}

Finally, if you are using RelayCommand, you can set the predicate of the command to the CanSave property, and the View will automatically enable or disable the button. In the ViewModel:

/// <summary>
/// Saves changes Command
/// </summary>
public ICommand SaveCommand
{
    get
    {
        if (_saveCommand == null)
            _saveCommand = new RelayCommand(param => this.SaveChanges(), param => this.CanSave);

        return _saveCommand;
    }
}

And in the View:

<Button Content="Save" Command="{Binding Path=SaveCommand}"/>

And that's it!

PS: If you haven't read Josh Smith's article yet, it will change your life.

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