In Android development, resource identifiers (IDs) used within annotations or as case values in switch statements must be compile-time constants. This means the value of the ID needs to be known during compilation, not determined at runtime. For instance, if a layout XML file defines a TextView with the ID `@+id/my_text_view`, the corresponding `R.id.my_text_view` value must be a final static integer. Any attempt to use a resource ID that is not a constant in these contexts will result in a compilation error.
The requirement for constant expression resource IDs ensures type safety and enables various compiler optimizations. By enforcing that IDs are known at compile time, the Android build tools can perform static analysis, verify correctness, and potentially inline values, leading to improved application performance and reduced runtime errors. Historically, this constraint has been essential for the efficient generation and utilization of resource tables, which map symbolic names to concrete values used by the Android system.
