In which type of UI control is reference data from a local data source most commonly used?

Dropdowns are primarily used when reference data from a local data source is required because they allow users to select from a predefined list of values. This is particularly useful for maintaining consistency and ensuring that the data entered matches the available options, thus reducing errors and enhancing the user experience.

In scenarios where users need to provide input based on a specific set of choices—like selecting a department from a list of all departments—dropdowns serve as the ideal control. They showcase the reference data clearly and enable users to make a selection without having to type in information manually, which can lead to typos or inconsistencies.

In contrast, text fields are more suited for free-format input, where users are expected to type in their responses without reference to a specific set of pre-defined options. Labels simply display static information and buttons act as interactive elements but do not serve to gather or present multiple-choice data. Thus, the dropdown control effectively integrates local reference data for a seamless selection experience.