Eval and Bind

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Data-binding expressions are contained within <%# and %> delimiters and use the Eval and Bind functions. The Eval function is used to define one-way (read-only) binding. The Bind function is used for two-way (updatable) binding. In addition to calling Eval and Bind methods to perform data binding in a data-binding expression, you can call any publicly scoped code within the <%# and %> delimiters to execute that code and return a value during page processing.

Data-binding expressions are resolved when the DataBind method of a control or of the Page class is called. For controls such as the GridView, DetailsView, and FormView controls, data-binding expressions are resolved automatically during the control's PreRender event and you are not required to call the DataBind method explicitly.