Importing Missing Namespaces
When you use types whose namespaces have not been imported in the file, Rider helps you locate these types and add the missing namespace import directives. If there are several missing namespaces for an unresolved type, e.g. after you paste a block of code in the file, Rider would help you import all these namespaces in a single action.
Rider looks for non-imported namespaces in the following assemblies: assemblies referenced in the current project, assemblies referenced in other projects in the solution, assemblies that are referenced transitively. If the type is found in an module that is not referenced in the current project, Rider also suggests adding a reference to this module.
The missing namespaces are imported according to your namespace import preferences (e.g. import directives are inserted or type names qualifiers are added).
The import directives are added in a fixed order: all
System.* namespaces go first, sorted alphabetically by the second word after the dot; all other namespaces go next, in alphabetical order.
When you edit a code file, types with missing namespaces are detected with the design-time code inspection and highlighted as errors. By default, the action that imports missing namespaces differs from the normal quick-fix: it is displayed as a pop-up that hovers either over the first unresolved symbol regardless of your caret position: or after a pasted code bock: Thus, you can apply this fix for all unresolved types with the habitual Alt+Enter shortcut without changing your current caret position, so your editing session is not interrupted. Note that the Import types for pasted code action only appears if all non-imported types in the pasted code block can be unambiguously found in the referenced modules of the current project.
In case several namespace contain the unresolved symbol, Rider lets you choose the namespace to import:
If for some reason you chose not to import a required namespace when the pop-up was displayed, just press Esc to hide the pop-up. You can import the namespace any time later by pressing Alt+Enter, and choosing the corresponding quick-fix.