public override void OnGUI( Rect rect, SerializedProperty property, GUIContent label )
{
var calculator = new Calculator();
var result = 0d;
var isValid = true;
try {
result = calculator.Evaluate( GetStringValue( property ) );
}
catch {
isValid = false;
}
var resultString = string.Format( " = {0}", result );
GUI.color = isValid ? Color.white : Color.red;
var contentPosition = EditorGUI.PrefixLabel( rect, label );
contentPosition.width -= resultStringSize;
SetStringValue( property, EditorGUI.TextField( contentPosition, GetStringValue( property ) ) );
GUI.color = Color.white;
contentPosition.x += contentPosition.width;
contentPosition.width = resultStringSize;
EditorGUI.LabelField( contentPosition, resultString );
}