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
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.