Add a warning icon to the TextBox when validation - wpf

Question

I want to validate a textbox if something is wrong. The idea is if something is wrong than the next TextBox should have a warning image.
<TextBox Text="{Binding Age, UpdateSourceTrigger=PropertyChanged}">
<Validation.ErrorTemplate>
<ControlTemplate>
<StackPanel>
<!-- Placeholder for the TextBox itself -->
<AdornedElementPlaceholder x:Name="textBox"/>
<image source="some-Image.png" width="20" Height="20" />
</StackPanel>
</ControlTemplate>
</Validation.ErrorTemplate>
</TextBox>
But the thing is the image is not showing, it only shows the border of the icon.
Am I using AdornedElementPlaceholder correctly?

Answer 1

Tested solution that works and displays the image when error occurs:
<TextBox BorderThickness="0.8">
<Validation.ErrorTemplate>
<ControlTemplate>
<StackPanel>
<AdornedElementPlaceholder/>
<Image Source="Image.jpg" Width="20" Height="20"/>
</StackPanel>
</ControlTemplate>
</Validation.ErrorTemplate>
<TextBox.Text>
<Binding Path="ValidationTest" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ValidatesOnDataErrors="True">
<Binding.ValidationRules>
<validation:IntegerValidationRule ValidationStep="CommittedValue" Min="1" Max="99999999"/>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
And here is the validation rule that I have used for this example:
public class IntegerValidationRule : ValidationRule
{
private int _min = int.MinValue;
private int _max = int.MaxValue;
private string _fieldName = "Field";
private string _customMessage = String.Empty;
public int Min
{
get { return _min; }
set { _min = value; }
}
public int Max
{
get { return _max; }
set { _max = value; }
}
public string FieldName
{
get { return _fieldName; }
set { _fieldName = value; }
}
public string CustomMessage
{
get { return _customMessage; }
set { _customMessage = value; }
}
public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
{
int num = 0;
var val = (value as BindingExpression).DataItem;
if (!int.TryParse(value.ToString(), out num))
return new ValidationResult(false, $"{FieldName} must contain an integer value.");
if (num < Min || num > Max)
{
if (!String.IsNullOrEmpty(CustomMessage))
return new ValidationResult(false, CustomMessage);
return new ValidationResult(false, $"{FieldName} must be between {Min} and {Max}.");
}
return new ValidationResult(true, null);
}
}
Which is just modified example from MSDN Docs
Some notes:
You didn't provide the validation rule so I am assuming it works as expected and produces valid validation result.
The Binding of your TextBox.Text property doesn't include the Validation rule.