Silverlight Databinding Question - silverlight

Question

I have a TextBox ( TextBoxConsumer ) and i would like to enable a button in my UI when the length of the TextBox.Text is greater than 3,
i digged it down to
IsEnabled="{Binding
ElementName=TextBoxConsumer,
Path=Text.Length}"
for my button's IsEnabled Property but im not sure how to find the length and convert it to bool depending on the length of the text box how do i do it?
i would like to do it entirely in Xaml instead of code using Binding instead of code

Answer 1

I would prefer to use an IValueConverter class for this. I'll provide some quick code though its not exactly what you are looking for you should be able to tweak it.
In a cs file by itself:
using System;
using System.Globalization;
using System.Windows.Data;
public class IntCorrectAnswerToTrueFalseConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return (int)value > 0;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return (bool)value ? 1 : 0;
}
}
In App.xaml, add this line to the ResourceDictionary:
<app:IntCorrectAnswerToTrueFalseConverter x:Key="IntCorrectAnswerToTrueFalseConverter" />
Then in the xaml of where you use it:
<CheckBox
x:Name="answerCheckBox"
IsChecked="{Binding Score, Converter={StaticResource IntCorrectAnswerToTrueFalseConverter}}"
Click="CheckBoxChecked"/>

Answer 2

I did something similar using a tutorial similar to this using the INotifyPropertyChanged interface. I assume you have a model you are using for binding to the UI. You have a string member (like TextBoxConsumerString) which binds to you textbox. Now you need to add a boolean like TextBoxConsumerEnabled which you will set inside of the setter of TextBoxConsumerString and call the notify changed method.
this.OnPropertyChanged( new PropertyChangedEventArgs( "TextBoxConsumerEnabled" ) );
Here is an example:
public class TextBoxConsumerModel : INotifyPropertyChanged
{
private string _textBoxConsumerString;
public event PropertyChangedEventHandler PropertyChanged;
public string TextBoxConsumerString
{
get
{
return _textBoxConsumerString;
}
set
{
if (_textBoxConsumerString == value)
return;
TextBoxConsumerEnabled = value != null && value.Length > 3;
_textBoxConsumerString = value;
OnPropertyChanged(new PropertyChangedEventArgs("TextBoxConsumerEnabled"));
}
}
public bool TextBoxConsumerEnabled { get; set; }
protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
{
if (PropertyChanged != null)
PropertyChanged(this, e);
}
}
That should be it as far as the model goes. Now you just need to bind to the two model properties from the XAML.