This FAQ is a topical index of questions that have been asked (and answered) on our OpenAPI forum. This is a work in progress.
How do I replace my usage of Project.getProjectFile() in 7.0?
How do I replace my usage of DataConstants with DataKeys in 7.0?
How do I replace my usage of ToolWindowManager.registerToolWindow() in 7.0?
How do I replace my usage of PsiSearchHelper.findReferences() in 7.0?
How do I replace my usage of DelayedFileStatusProvider in 6.0?
How do I trigger actions programmatically?
How do I add a main menu item?
How do I customize the "New..." menu?
How do I customize the compiler output context menu?
How do I get the context of an action (selected file, active project etc.)?
How do I change the icon of an action dynamically?
How do I add icons to the IDEA toolbar?
Where do I get the list of built-in action IDs?
Accessing and Modifying the Source Code
How do I find all subclasses of a class?
How do I find all anonymous classes created in a class?
How do I calculate the value of a string literal token?
How do I rename or move a Java class?
How do I build the list of all classes used by a given class or package?
How do I insert whitespace into the PSI?
How do I add properties to a .properties file?
How do I find specific method calls inside a PsiMethod?
What is the lifecycle of a PSI element?
How do I find a file given its name (but no path)?
How do I create a new class in the given package?
How do I make a PsiClass extend another PsiClass?
How do I find references to a class from non-Java files?
How do I find the source file given the path to a .class file?
How do I find classes with the specified non-qualified name?
How do I find the module in which a class is located?
Working with XML and XML DOM
How do I change the value of an XML attribute through the PSI?
How do I add custom references to Java elements in XML files?
How do I programmatically register a DTD or schema?
What is the "strict" parameter in DomElement.getParentOfType()?
Version Control Integration
Can I provide line status markers for files in a custom file system?
How do I update the state of VCS actions depending on file status?
How can I find out the module of a deleted file?
Can I provide additional decorations for changelists in the Changes view?
How do I report out-of-date files?
Why are the extension elements in my plugin.xml red?
How can I read the plugin descriptor of my plugin from code?
How do I provide a custom exception reporter for my plugin?
How can I add the help topics of my plugin to the IntelliJ IDEA help system?
How do I get the version of IntelliJ IDEA under which my plugin is running?
Editors, Documents and Files
Why doesn't the file change on disk after I changed it through the PSI?
Can I hook into the file save logic?
Can I mark a part of a file as read-only? How do I control what happens when the user tries to edit such a part?
How do I implement a custom editor?
How can I show several editors for a single file in tabs?
Can I open an editor which has no underlying file on disk?
How do I save the content of my custom editor when the user saves all documents?
How do I highlight elements in a source code editor? How do I allow to navigate between highlighted elements using Find Next?
How do I force code to be re-analyzed?
How do I get the active editor instance?
How do I get the cursor position in the current editor?
How do I clear the read-only status of a file?
How do I show a popup hint in an editor?
How do I create live template-like red box edit regions in an editor?
How can I show an editor with error highlighting in a toolwindow?
Can I build an inspection that processes XML files?
Why are the inspection results shown multiple times?
How can I provide a quick fix that creates a method?
Is it possible to inspect only the elements that have been modified after the last full inspection?
How do I provide Parameter Info support for my language?
How do I provide auto-popup code completion in my language?
How to make a closing brace unindent?
How to automatically insert closing quotes?
How do I provide Ctrl+mouse popups for my language?
How do I enable debugging for my custom language which is compiled into Java?
How do I generate virtual Java classes mirroring the classes of my language?
How do I provide animated status bar notifications?
How do I enable file name completion in a combobox?
How do I show a popup with left-aligned and right-aligned parts for each item?
Can I use an embedded Web browser from my plugin?
How do I provide a custom icon for files/PSI elements?
Can I show a progress indicator for WriteActions?
How do I make it possible to search the options of my plugin in the Settings dialog?
How do I show a custom window or popup based on Structure View?
Is it possible to extend the Project View tree?
How do I show the "Project Structure" dialog programmatically?
How do I print messages in the console view?
How do I show the package selector dialog programmatically?
How do I provide syntax and error highlighting in a combo box editor?
How can I get notified when my toolwindow is activated?
How can I provide Close and Rerun buttons in my Usage View window?
How do I get the currently active project outside of an AnAction?
How do I detect when a project is closing?
How can I implement a custom stack trace analyzer?
Where is the state of an ApplicationComponent stored?
How do I open a project programmatically?
How do I get the folder of the currently selected file?
How do I encrypt some values in the configuration data of my plugin?
How can I track exceptions from my plugin?
Thanks to Sascha Weinreuter, Hugo Palma and Jay 'sliding' BS for their help in compiling the FAQ.