Inside Macintosh: Programmer's Guide to MacApp / Part 2 - Working With MacApp

Chapter 13 -
Working With Events and Commands

This chapter provides recipes and sample code that demonstrate how to

• create a command object to perform an action (a general outline)
• implement an undoable Zoom In menu command
• change the current target object and perform validation
• ensure idle time for an event-handler object when it's not in the target chain
• use a behavior object to implement alphabetic type-ahead

For an overview of event handling in MacApp, see Chapter 1, "MacApp Overview."

For a detailed description of event dispatching and the use of command objects to respond to events, see Chapter 5, "Events and Commands."

For a description of Apple event dispatching, see Chapter 6, "Scripting."

For information on working with Apple events, see Chapter 14, "Working With Scripting."

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Chapter Contents

Overview

Which Object Should Handle an Event or Menu Command

Working With Behaviors

Recipes--Events and Commands

Creating a Command Object to Perform an Action--A General Overview

Recipe--Implementing an Undoable Zoom In Menu Command

Define a Command-Number Constant for the Zoom In Menu Item

Add the Zoom In Menu Item to a 'CMNU' Resource

Implement a Command Class That Handles Zoom In

The IZoomInCommand Method

The DoIt Method

The RedoIt Method

The UndoIt Method

Override DoSetupMenus in the View Class

Override DoMenuCommand in the Document Class

Recipe--Changing the Current Target Object and Performing Validation

Changing the Current Target Object

Performing Validation When a Target Change Is Attempted

Recipe--Ensuring Idle Time for an Event-Handler Object

Override the DoIdle Method

Install the Object in the Cohandler Chain

Set the fIdleFreq Field to Specify How Often DoIdle Should Be Called

Remove the Object From the Cohandler Chain

Recipe--Using a Behavior Object to Implement Alphabetic Type-Ahead

Define a View Class That Descends From TTextListView

Add a TKeySelectionBehavior Behavior to the View Object