C# WPF very simple TextBox Validation

Question

i'm a total Beginner at C#.... I'd like to create a very simple Validation for a TextBox. Here is my Code so far: MainWindow.xaml.cs ``` namespace Mynamespace { public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); } private void TextBox_TextChanged_2(object sender, TextChangedEventArgs e) { } } public class AgeValidationRule : ValidationRule { public override ValidationResult Validate(object value, CultureInfo cultureInfo) { int wert = Convert.ToInt32(value); if (wert < 0) return new ValidationResult(false, "just positiv values allowed"); return new ValidationResult(true, null); } } } ``` MainWindow.xaml ```

Accepted Answer

TextBox is supposed to be bound to property `Alter`. For binding to work you need to set DataContext - an object with `Alter` property, e.g.

```
public class Test
{
    public string Alter { get; set; }
}
```

and

```
public MainWindow()
{
    InitializeComponent();
    DataContext = new Test();
}
```

then if you enter negative number, there will be red border around TextBox

C# WPF very simple TextBox Validation

Solution

Problem