我进行了广泛的搜索，如果文本在 Cocoa 中太大，我终生无法找到有关如何实现与 iTunes 歌曲标题滚动类似效果的任何信息。我尝试在 NSTextField 上设置边界无济于事。我尝试过使用 NSTextView 以及使用 NSScrollView 的各种尝试。我确信我错过了一些简单的东西，但任何帮助将不胜感激。如果可能的话，我也希望不必使用 CoreGraphics。
Example，注意“Base.FM http://www”。文本已滚动。如果您需要一个更好的示例，请打开 iTunes，其中有一首标题相当大的歌曲，然后观看它来回滚动。
我认为肯定有一种简单的方法可以使用 NSTextField 和 NSTimer 创建选取框类型效果，但是唉。
【问题讨论】：
标签： objective-c cocoa itunes nstextfield nsscrollview
如果您试图将功能硬塞到现有控件中，我可以看到这将是多么困难。但是，如果你只是从一个普通的 NSView 开始，那还不错。我在大约 10 分钟内完成了这个...
//ScrollingTextView.h:
#import <Cocoa/Cocoa.h>
@interface ScrollingTextView : NSView {
NSTimer * scroller;
NSPoint point;
NSString * text;
NSTimeInterval speed;
CGFloat stringWidth;
}
@property (nonatomic, copy) NSString * text;
@property (nonatomic) NSTimeInterval speed;
@end
//ScrollingTextView.m
#import "ScrollingTextView.h"
@implementation ScrollingTextView
@synthesize text;
@synthesize speed;
- (void) dealloc {
[text release];
[scroller invalidate];
[super dealloc];
}
- (void) setText:(NSString *)newText {
[text release];
text = [newText copy];
point = NSZeroPoint;
stringWidth = [newText sizeWithAttributes:nil].width;
if (scroller == nil && speed > 0 && text != nil) {
scroller = [NSTimer scheduledTimerWithTimeInterval:speed target:self selector:@selector(moveText:) userInfo:nil repeats:YES];
}
}
- (void) setSpeed:(NSTimeInterval)newSpeed {
if (newSpeed != speed) {
speed = newSpeed;
[scroller invalidate];
scroller == nil;
if (speed > 0 && text != nil) {
scroller = [NSTimer scheduledTimerWithTimeInterval:speed target:self selector:@selector(moveText:) userInfo:nil repeats:YES];
}
}
}
- (void) moveText:(NSTimer *)timer {
point.x = point.x - 1.0f;
[self setNeedsDisplay:YES];
}
- (void)drawRect:(NSRect)dirtyRect {
// Drawing code here.
if (point.x + stringWidth < 0) {
point.x += dirtyRect.size.width;
}
[text drawAtPoint:point withAttributes:nil];
if (point.x < 0) {
NSPoint otherPoint = point;
otherPoint.x += dirtyRect.size.width;
[text drawAtPoint:otherPoint withAttributes:nil];
}
}
@end
只需将 NSView 拖到 Interface Builder 中的窗口上，然后将其类更改为“ScrollingTextView”。然后（在代码中），你这样做：
[myScrollingTextView setText:@"This is the text I want to scroll"];
[myScrollingTextView setSpeed:0.01]; //redraws every 1/100th of a second
这显然是非常初级的，但它可以包含您正在寻找的东西，并且是一个不错的起点。
【讨论】：
对于在 Swift 4 中寻找此功能的任何人，我已经转换了 Dave 的答案并添加了更多功能。
import Cocoa
open class ScrollingTextView: NSView {
/// Text to scroll
open var text: NSString?
/// Font for scrolling text
open var font: NSFont?
/// Scrolling text color
open var textColor: NSColor = .headerTextColor
/// Determines if the text should be delayed before starting scroll
open var isDelayed: Bool = true
/// Spacing between the tail and head of the scrolling text
open var spacing: CGFloat = 20
/// Amount of time the text is delayed before scrolling
open var delay: TimeInterval = 2 {
didSet {
updateTraits()
}
}
/// Length of the scrolling text view
open var length: CGFloat = 0 {
didSet {
updateTraits()
}
}
/// Speed at which the text scrolls. This number is divided by 100.
open var speed: Double = 4 {
didSet {
updateTraits()
}
}
private var timer: Timer?
private var point = NSPoint(x: 0, y: 0)
private var timeInterval: TimeInterval?
private(set) var stringSize = NSSize(width: 0, height: 0) {
didSet {
point.x = 0
}
}
private var timerSpeed: Double? {
return speed / 100
}
private lazy var textFontAttributes: [NSAttributedString.Key: Any] = {
return [NSAttributedString.Key.font: font ?? NSFont.systemFont(ofSize: 14)]
}()
/**
Sets up the scrolling text view
- Parameters:
- string: The string that will be used as the text in the view
*/
open func setup(string: String) {
text = string as NSString
stringSize = text?.size(withAttributes: textFontAttributes) ?? NSSize(width: 0, height: 0)
setNeedsDisplay(NSRect(x: 0, y: 0, width: frame.width, height: frame.height))
updateTraits()
}
}
private extension ScrollingTextView {
func setSpeed(newInterval: TimeInterval) {
clearTimer()
timeInterval = newInterval
guard let timeInterval = timeInterval else { return }
if timer == nil, timeInterval > 0.0, text != nil {
if #available(OSX 10.12, *) {
timer = Timer.scheduledTimer(timeInterval: newInterval, target: self, selector: #selector(update(_:)), userInfo: nil, repeats: true)
guard let timer = timer else { return }
RunLoop.main.add(timer, forMode: .commonModes)
} else {
// Fallback on earlier versions
}
} else {
clearTimer()
point.x = 0
}
}
func updateTraits() {
clearTimer()
if stringSize.width > length {
guard let speed = timerSpeed else { return }
if #available(OSX 10.12, *), isDelayed {
timer = Timer.scheduledTimer(withTimeInterval: delay, repeats: false, block: { [weak self] timer in
self?.setSpeed(newInterval: speed)
})
} else {
setSpeed(newInterval: speed)
}
} else {
setSpeed(newInterval: 0.0)
}
}
func clearTimer() {
timer?.invalidate()
timer = nil
}
@objc
func update(_ sender: Timer) {
point.x = point.x - 1
setNeedsDisplay(NSRect(x: 0, y: 0, width: frame.width, height: frame.height))
}
}
extension ScrollingTextView {
override open func draw(_ dirtyRect: NSRect) {
if point.x + stringSize.width < 0 {
point.x += stringSize.width + spacing
}
textFontAttributes[NSAttributedString.Key.foregroundColor] = textColor
text?.draw(at: point, withAttributes: textFontAttributes)
if point.x < 0 {
var otherPoint = point
otherPoint.x += stringSize.width + spacing
text?.draw(at: otherPoint, withAttributes: textFontAttributes)
}
}
override open func layout() {
super.layout()
point.y = (frame.height - stringSize.height) / 2
}
}
参考要点： https://gist.github.com/NicholasBellucci/b5e9d31c47f335c36aa043f5f39eedb2
【讨论】：