在 CATextLayer 中显示属性字符串

问题描述

我有一个简单的示例应用程序，我在其中创建了一个 CATextLayer 并将其 string 属性设置为 NSAttributedString.然后我将该 CATextLayer 添加到视图中.

I have a simple example app where I create a CATextLayer and set its string property to an NSAttributedString. I then add that CATextLayer to a view.

#import <CoreText/CoreText.h>
#import <QuartzCore/QuartzCore.h>

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    CTFontRef fontFace = CTFontCreateWithName((__bridge CFStringRef)(@"HelfaSemiBold"), 24.0, NULL);
    NSMutableDictionary *attributes = [[NSMutableDictionary alloc] init];
    [attributes setObject:(__bridge id)fontFace forKey:(NSString*)kCTFontAttributeName];
    [attributes setObject:[UIColor blueColor] forKey:(NSString*)kCTForegroundColorAttributeName];
    NSAttributedString *attrStr = [[NSAttributedString alloc] initWithString:@"Lorem Ipsum" attributes:attributes];

    CATextLayer *textLayer = [CATextLayer layer];
    textLayer.backgroundColor = [UIColor whiteColor].CGColor;
    textLayer.frame = CGRectMake(20, 20, 200, 100);
    textLayer.contentsScale = [[UIScreen mainScreen] scale];
    textLayer.string = attrStr;

    [self.view.layer addSublayer:textLayer];
}

这在模拟器中效果很好，除了文本是黑色而不是蓝色.在设备上运行时，一切都会像在模拟器上一样显示，但会在控制台中生成以下两个错误.

This works great in the simulator except the text is black instead of blue. When running on a device everything displays like it does on the simulator but it generates the following two errors in the console.

<Error>: CGContextSetFillColorWithColor: invalid context 0x0
<Error>: CGContextSetStrokeColorWithColor: invalid context 0x0

我应该在某处设置 CGContext 吗?我的属性设置错了吗?我是不是完全走错了轨道.请注意，这是针对 iOS 5.x 应用程序的，出于性能原因，我想使用 CATextLayer.真正的应用程序将有许多 CATextLayers.

Should I be setting a CGContext somewhere? Am I setting my attributes wrong? Am I completely on the wrong track. Note, this for an iOS 5.x app and I want to use a CATextLayer for performance reasons. The real app is going to have many CATextLayers.

推荐答案

kCTForegroundColorAttributeName 必须使用 CGColor 而不是 UIColor :>

You must use CGColor instead of UIColor for kCTForegroundColorAttributeName:

[attributes setObject:(__bridge id)[UIColor blueColor].CGColor
               forKey:(NSString *)kCTForegroundColorAttributeName];

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