其他 - Xcode Objective-C：下载自定义字体并将其显示在UILabel中

首先：是否可以下载自定义字体并将其显示在UILabel中？

我正在使用此代码从Internet下载自定义字体并将其显示在UILabel中，但是它不起作用。

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

@synthesize txt_UserName;

- (void)viewDidLoad {
    [super viewDidLoad];

    // 1
    NSString *dataUrl = @"https://dl.dafont.com/dl/?f=stars_fighters";
    NSURL *url = [NSURL URLWithString:dataUrl];

    // 2
    NSURLSessionDataTask *downloadTask = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        // 4: Handle response here
        if (error == nil) {
            NSLog(@"no error!");
            if (data != nil) {
                NSLog(@"There is data!");
                [self loadFont:data];
            }
        } else {
            NSLog(@"%@", error.localizedDescription);
        }
    }];

    // 3
    [downloadTask resume];


}

- (void)loadFont:(NSData *)data
{
    NSData *inData = data;
    CFErrorRef error;
    CGDataProviderRef provider = CGDataProviderCreateWithCFData((CFDataRef)data);
    CGFontRef font = CGFontCreateWithDataProvider(provider);
    if(!CTFontManagerRegisterGraphicsFont(font, &error)){
        CFStringRef errorDescription = CFErrorCopyDescription(error);
        NSLog(@"Failed to load font: %@", errorDescription);
      //  CFRelease(errorDescription);
    }
//    CFRelease(font);
 //   CFRelease(provider);

    CTFontRef ctFont = CTFontCreateWithGraphicsFont(font, 30, NULL, NULL);
    UIFont *uiFont = CFBridgingRelease(ctFont);

    dispatch_async(dispatch_get_main_queue(), ^{
        [self.txt_UserName setFont:uiFont];
    });

    [self fontTest];
}

- (void)fontTest
{
    NSArray *fontFamilies = [UIFont familyNames];
    for (int i = 0; i < [fontFamilies count]; i++) {
        NSString *fontFamily = [fontFamilies objectAtIndex:i];
        NSArray *fontNames = [UIFont fontNamesForFamilyName:[fontFamilies objectAtIndex:i]];
        NSLog (@"%@: %@", fontFamily, fontNames);
    }
}

@end  

无论如何，我遇到此错误： 无法加载字体：操作无法完成。无效的论点

在自定义字体的位置，我获得了默认的iOS字体。