PSI file

一个PSI file 展示PSI元素（PSI树），一个单个的PSI file可能包含许多PSI树，一个PSI元素可以有子PSI元素。例如，可以使用PSI元素执行代码分析，如代码检查或目的操作。

The PsiElement class is the common base class for PSI elements.

How do I get a PSI element?

• From an action: e.getData(LangDataKeys.PSI_ELEMENT). Note: if an editor is currently open and the element under caret is a reference, this will return the result of resolving the reference. This may or may not be what you need.

• From a file by offset: PsiFile.findElementAt(). Note: this returns the lowest level element at the specified offset, which is normally a lexer token. Most likely you should use PsiTreeUtil.getParentOfType() to find the element you really need.

• By iterating through a PSI file: using a PsiRecursiveElementWalkingVisitor.

• By resolving a reference: PsiReference.resolve()