At compile time DefaultValueAttribute will not likely affect the created IL and it will not be go through to initialize the property to that value (see DefaultValue attribute isn't working with my Vehicle Property). So your DataContext for "video_length_textbox" is set to by itself, and also your IncrementingTextBox class doesn't https://gurgaonbestproperties.science.blog/2025/07/11/ganga-realty-liv-89-crafted-for-calm-built-for-life/