The PSI needs to be able to display icons to help identify code elements in completion, navigation or find usage result lists. The PSI can display different icons to distinguish between classes, constructors, methods, parameters, etc. It can also show specific icons for CSS class IDs, HTML elements and unit test elements.
While the Shell provides the
ThemedIconManager class in order to load and create icons, it is a low level API. It provides no means for getting the icon for a class, other than explicitly loading
PsiSymbolsThemedIcons.Class.Id. The PSI provides the
PsiIconManager to retrieve icons for a specific declared element.
PsiIconManager provides the following methods and properties:
PsiIconExtension type is a flags based enum, which provides the modifiers, such as public, private, internal, or abstract, virtual, static, etc. These modifiers are used to create a composite icon, with the base icon representing the element being overlayed with another icon that represents the modifier.
GetDummyImagereturns a dummy, placeholder image, which is to be used if the icon manager cannot return a more specific image. The pattern for usage is usually:var iconId = manager.GetImage(CLRDeclaredElementType.CONSTRUCTOR) ?? manager.GetDummyImage();
GetImageprovides several overloads. The first takes an instance of
IDeclaredElement, and will return an icon specific to that element, for example, given an element for a class declaration, the method will return an
IconIdfor the class icon. The
drawExtensionsparameter is true if the element's modifiers (public, private, abstract, etc.) are used to modify the icon.
The other overloads use an instance of
DeclaredElementType, which is a metadata class that describes how various declared element types are presented, including presentable name and which icon to use. ReSharper ships with several classes that describe element types, such as
WebConfigDeclaredElementType. Each class has several static fields that provide instances of the element type, such as
AttachExtensionswill add the expected modifier overlays to the passed icon, marking it as private, protected, abstract, static, etc.
KeywordIconsimply returns the
IconIdof the icon representing keywords.
Typically, the icon manager will return an icon when
GetImage is called. If it returns
null, use the image returned by
Extending the icon manager
By default, the icon manager will try to return a specific icon for a given declared element. If it can't find one, it returns the icon from the element's
DeclaredElementType. In order to find a specific icon, it asks an extensible collection of icon providers, which all implement the
ReSharper ships with a number of language specific providers, such as the C# provider that checks to see if the declared element is a C# extension method, indexer property or finalizer (all of which would otherwise be classed as a simple method), and returns back a specific icon in each case. If the element isn't one of these, it returns null. It also returns
true in the
canApplyExtensions parameter to indicate that this element can have modifiers, based on
Furthermore, ReSharper ships with a colour icon provider, which recognises type members that are colour properties, and returns a
ColorIconId to match. This provider returns
canApplyExtensions. ReSharper also ships a unit test icon provider, which checks to see if the declared element is part of a unit test, and returns an appropriate unit test icon.
The collection can be extended by creating a class that implements
IDeclaredElementIconProvider and is decorated with the
[DeclaredElementIconProvider] attribute. This scopes the class to PSI-shared component lifetime (that is, the same lifetime as a
ShellComponent). Should the class need to have a narrower lifetime, such as
[SolutionComponent], it is possible to call
PsiIconManager.AddExtension in the provider's constructor, passing in it's own
Lifetime for cleanup. The unit test icon provider does this, as it depends on components that have solution lifetime scope.
IDeclaredElementIconExtensionProvider can be implemented to extend the process for deciding what modifiers should be applied to the icon (private, public, etc.). The class should be decorated with the
[DeclaredElementIconExtensionProvider] attribute, or can also be registered by calling
PsiIconManager.AddExtension if the component has different lifetime requirements. This provider is currently implemented for CLR and C++ elements.