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Copyright (c) 1994 by NeXT Computer, Inc. All Rights Reserved.


Inherits From: NSControl : NSView : NSResponder : NSObject

Conforms To: NSCoding (NSResponder) NSObject (NSObject)

Declared In: AppKit/NSScroller.h

Class Description

The NSScroller class defines a control that's used by an NSScrollView object to position a document that's too large to be displayed in its entirety within an NSView. An NSScroller is typically represented on the screen by a bar, a knob, and two scroll buttons, although it may contain only some of these. The knob indicates both the position within the document and the amount displayed relative to the size of the document. The bar is the rectangular region that the knob slides within. The scroll buttons allow the user to scroll in small increments by clicking, or in large increments by Alternate-clicking. In discussions of the NSScroller class, a small increment is referred to as a line increment (even if the NSScroller is oriented horizontally), and a large increment is referred to as a page increment, although a page increment actually advances the document by one windowful. When you create an NSScroller, you can specify either a vertical or a horizontal orientation.

As an NSControl, an NSScroller handles mouse events and sends action messages to its target (usually its parent NSScrollView) to implement user-controlled scrolling. The NSScroller must also respond to messages from an NSScrollView to represent changes in document positioning.

NSScroller is a public class primarily for programmers who decide not to use an NSScrollView but want to present a consistent user interface. Its use is not encouraged except in cases where the porting of an existing application is made more straightforward. In these situations, you initialize a newly created NSScroller by calling initWithFrame:. Then, you use setTarget: (NSControl) to set the object that will receive messages from the NSScroller, and you use setAction: (NSControl) to specify the message that will be sent to the target by the NSScroller. When your target receives a message from the NSScroller, it will probably need to query the NSScroller using the hitPart and floatValue (NSControl) methods to determine what action to take.

The NSScroller class has several constants referring to the parts of an NSScroller. A scroll button with an up arrow (or left arrow, if the NSScroller is oriented horizontally) is known as a decrement line button if it receives a normal click, and as a decrement page button if it receives an Alternate-click. Similarly, a scroll button with a down or right arrow functions as both an increment line button and an increment page button. The constants defining the parts of an NSScroller are as follows:

Constant Refers To

NSScrollerNoPart No part of the NSScroller

NSScrollerKnob The knob

NSScrollerDecrementPage The button that decrements a windowful (up or left arrow)

NSScrollerIncrementPage The button that increments a windowful (down or right arrow)

NSScrollerDecrementLine The button that decrements a windowful (up or left arrow)

NSScrollerIncrementLine The button that increments a windowful (down or right arrow)

NSScrollerKnobSlot The bar

The following constants are used in the setArrowsPosition: method to set the position of the scroll buttons within the scroller:

Constant Meaning

NSScrollerArrowsMaxEnd Scroll buttons are placed at the bottom or right end of the scroller.

NSScrollerArrowsMinEnd Scroll buttons are placed at the top or left part of the scroller.

NSScrollerArrowsNone The scroller doesn't have scroll buttons.

An NSScroller can be made too small for all its parts to be displayed. The usableParts method returns one of the following constants to indicate whether such a condition is present:

Constant Meaning

NSNoScrollerParts Scroller has no usable parts, only the bar.

NSOnlyScrollerArrows Scroller has only scroll buttons.

NSAllScrollerParts Scroller has all parts.

The following constants are used as values for the first argument of the drawArrow:highlight: method, to indicate which scroll button is to be drawn:

Constant Meaning

NSScrollerIncrementArrow The scroll button that scrolls forward.

NSScrollerDecrementArrow The scroll button that scrolls backward.

Laying out the NSScroller

Setting the NSScroller's Values


Handling Events