cocoa - 在 Swift 中创建 CTTypesetter

Question

我有一个创建 CFAttributedStringRef 的 obj-c 类:

- (CFAttributedStringRef)createAttributedStringWithByteRange:(NSRange)byteRange
{
  UInt8 bytes[byteRange.length];
  [self.data getBytes:&bytes range:byteRange];

  CFStringRef string = CFStringCreateWithBytes(NULL, bytes, byteRange.length, kCFStringEncodingUTF8, (byteRange.location == 0));

  return CFAttributedStringCreate(NULL, string, (__bridge CFDictionaryRef)(self.textAttributes));
}

我正在尝试从 swift 对象调用该函数，该对象应该创建一个 CTTypesetter:

let stringToDraw = self.storage.createAttributedStringWithByteRange(self.line.range)
let typesetter = CTTypesetterCreateWithAttributedString(stringToDraw)

这给了我这个构建错误:

error: cannot convert the expression's type 'CTTypesetter!' to type '$T3'
let typesetter = CTTypesetterCreateWithAttributedString(stringToDraw)
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

有人知道我做错了什么吗？

Answer 1

我发现了问题，构建错误具有误导性。

实际问题是前一行 - 我的 obj-c 方法返回 CFAttributedStringRef桥接Unmanaged<CFAttributedString>并需要通过 takeRetainedValue() 将其作为托管对象引入 Swift 才能使用。方法:

let stringToDraw = self.storage.createAttributedStringWithByteRange(self.line.range).takeRetainedValue()
let typesetter = CTTypesetterCreateWithAttributedString(stringToDraw)