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Standard Action Methods for Selecting and Editing

The NSResponder class declares method prototypes for a number of standard action methods, nearly all related to manipulating selections and editing text. These methods are typically invoked through doCommandBySelector: as a result of interpretation by the input manager. They fall into the following general groups:

• Selection movement and expansion

• Text insertion

• General deletion of elements

• Modifying selected text

• Scrolling a document

In most cases the intent of the action method is clear from its name. The individual method descriptions in this specification also provide detailed information about what such a method should normally do. However, a few general concepts apply to many of these methods, and are explained here.

In this section:

Selection Direction
Selection and insertion point
Marks
The kill buffer

Selection Direction

Some methods refer to spatial directions; left, right, up, down. These are meant to be taken literally, especially in text. To accommodate writing systems with directionality different from Latin script, the terms forward, beginning, backward, and end are used.

Selection and insertion point

Methods that refer to moving, deleting, or inserting imply that some elements in the responder are selected, or that there’s a zero-length selection at some location (the insertion point). These two things must always be treated consistently. For example, the insertText: method is defined as replacing the selection with the text provided. The moveForwardAndModifySelection: method extends or contracts a selection, even if the selection is merely an insertion point. When a selection is modified for the first time, it must always be extended. So a moveForward... message extends the selection from its end, while a moveBackward... message extends it from its beginning.

Marks

A number of action methods for editing text imitate the Emacs concepts of point (the insertion point), and mark (an anchor for larger operations normally handled by selections in graphical interfaces). The setMark: method establishes the mark at the current selection, which then remains in effect until the mark is changed again. The selectToMark: method extends the selection to include the mark and all characters between the selection and the mark.

The kill buffer

Also like Emacs, deletion methods affecting lines, paragraphs, and the mark implicitly place the deleted text into a buffer, separate from the pasteboard, from which you can later retrieve it. Methods such as deleteToBeginningOfLine: add text to this buffer, and yank: replaces the selection with the item in the kill buffer.

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