如何用Swift编写这段代码？

Question

我有一段用Objective-C编写的代码：

NSRect textRect = NSMakeRect(42, 35, 117, 55);
{
    NSString* textContent = @"Hello, World!";
    NSMutableParagraphStyle* textStyle = NSMutableParagraphStyle.defaultParagraphStyle.mutableCopy;
    textStyle.alignment = NSCenterTextAlignment;

    NSDictionary* textFontAttributes = @{NSFontAttributeName: [NSFont fontWithName: @"Helvetica" size: 12], NSForegroundColorAttributeName: NSColor.blackColor, NSParagraphStyleAttributeName: textStyle};

    [textContent drawInRect: NSOffsetRect(textRect, 0, 1 - (NSHeight(textRect) - NSHeight([textContent boundingRectWithSize: textRect.size options: NSStringDrawingUsesLineFragmentOrigin attributes: textFontAttributes])) / 2) withAttributes: textFontAttributes];
}

现在，我想用Swift编写这段代码。以下是我目前的代码：

let textRect = NSMakeRect(42, 35, 117, 55)
let textTextContent = NSString(string: "Hello, World!")
let textStyle = NSMutableParagraphStyle.defaultParagraphStyle().mutableCopy() as NSMutableParagraphStyle
textStyle.alignment = NSTextAlignment.CenterTextAlignment

let textFontAttributes = [NSFontAttributeName: NSFont(name: "Helvetica", size: 12), NSForegroundColorAttributeName: NSColor.blackColor(), NSParagraphStyleAttributeName: textStyle]

textTextContent.drawInRect(NSOffsetRect(textRect, 0, 1 - (NSHeight(textRect) - NSHeight(textTextContent.boundingRectWithSize(textRect.size, options: NSStringDrawingOptions.UsesLineFragmentOrigin, attributes: textFontAttributes))) / 2), withAttributes: textFontAttributes)

这行有误：

   let textFontAttributes = [NSFontAttributeName: NSFont(name: "Helvetica", size: 12), NSForegroundColorAttributeName: NSColor.blackColor(), NSParagraphStyleAttributeName: textStyle]

那行代码有什么问题？

这是编译器的错误：

"找不到接受所提供参数的“init”的重载。"

- C-Viorel

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那行代码有什么问题？Xcode 应该会显示一些错误信息。 - Sebastian Wramba

找不到接受提供的参数的“init”重载。这是错误。我尝试使用较少的属性，但仍收到相同的错误。 - C-Viorel

Answer 1

Swift的类型推断失败了，因为您要添加到字典中的字体是可选的。 NSFont（name：size :) 返回一个可选的 NSFont？，您需要一个解包版本。为了进行防御性编码，您需要像这样的代码：

// get the font you want, or the label font if that's not available
let font = NSFont(name: "Helvetica", size: 12) ?? NSFont.labelFontOfSize(12)

// now this should work
let textFontAttributes = [NSFontAttributeName: font, NSForegroundColorAttributeName: NSColor.blackColor(), NSParagraphStyleAttributeName: textStyle]

- Nate Cook

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太棒了！非常感谢你。 - C-Viorel