Setting Up Input Server Classes

To create an input server, you can either subclass NSInputServer or instantiate an NSInputServer object with a delegate. The second choice normally suffices. If you choose to subclass NSInputServer, you usually override most or all of the methods required by the NSInputServiceProvider protocol. If you assign a delegate object, the delegate must implement the NSInputServiceProvider protocol.

Tracking Input Clients

The input management classes identify each text-modification message with a client and a conversation identifier. Clients are instances of the NSInputManager class associated with applications, and conversation identifiers specify the text views within applications. The input server talks to multiple clients (applications), and each client controls multiple conversations (text views).

Unless your input server processes only single characters, it needs a way to keep track of multiple clients and conversations. A straightforward way to do this is to define a context object class to handle individual input clients, and map clients to context objects with a dictionary. You can convert the addresses of client objects (pointers) to NSNumber objects, and use the resulting NSNumber as a key for the context object. The following C macro converts client addresses to NSNumber keys:

#define KEY_FROM_CLIENTID(theClient) ([NSNumber numberWithUnsignedInt:

                                            (unsigned int)theClient])

Additionally, within each context object, you need to map conversation numbers (type long) to check that input server messages correspond to the current conversation. You can again use a dictionary or other data structure to perform the mapping.

Managing Marked Text

Input servers can manage an active portion of a text view, called the marked text, which is visually marked so the user knows it is not final. To set the marked text range, use the input client’s setMarkedText:selectedRange: method. To retrieve the current marked range, use the markedRange method. This code fragment replaces the current marked range with the string outputBuffer in the text input client client and sets the selected range to the new string:

id client;              // Assume this exists and implements NSTextInput.

NSString *outputBuffer; // Assume this exists.

[client setMarkedText:outputBuffer

        selectedRange:NSMakeRange(0,[outputBuffer length]);

To unmark the text in a client view, use the NSTextInput unmarkText method.

To retrieve the text formatting attributes supported by a client view, use the validAttributesForMarkedText method. See the additions to NSAttributedString in the Application Kit for the set of string constants supported by the view.

Tracking Mouse Events

To make an input server receive mouse events—for example, to handle selection—as well as keyboard events, you should implement its wantsToHandleMouseEvents to return YES. Additionally, to handle mouse events the input server must implement the NSInputServerMouseTracker protocol, which consists of three methods: mouseDownOnCharacterIndex:atCoordinate:withModifier:client:, mouseDraggedOnCharacterIndex:atCoordinate:withModifier:client:, and mouseUpOnCharacterIndex:atCoordinate:withModifier:client:, for mouse-down, mouse-dragged, and mouse-up events, respectively.