At compile time DefaultValueAttribute will never effect the created IL and it won't be study to initialize the property to that value (see DefaultValue attribute will not be working with my Vehicle Property). So your DataContext for "video_length_textbox" is set to alone, plus your IncrementingTextBox class doesn't have a general https://pyramidsector71.blogspot.com/2025/07/aipl-sector-103-gurgaon-wellness-living.html