objective-c - 如何快速编写这段代码？

Question

我有这段代码是用 Objective c 写的:

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。这是我到目前为止所得到的:

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)

这一行是错误的:

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

那一行有什么问题？

这是编译器的错误:

"Could not find an overload for “init” that accepts the supplied arguments".

Answer 1

Swift 的类型推断让您失望，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?，你需要一个未包装的版本。要进行防御性编码，您需要这样的东西:

// 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]