Question

我试图从此处转换以下Objective-C代码（source）

-(CGRect) dimensionsForAttributedString: (NSAttributedString *) asp {

    CGFloat ascent = 0, descent = 0, width = 0;
    CTLineRef line = CTLineCreateWithAttributedString( (CFAttributedStringRef) asp);

    width = CTLineGetTypographicBounds( line, &ascent, &descent, NULL );

    // ...
}

进入Swift：

func dimensionsForAttributedString(asp: NSAttributedString) -> CGRect {

    let ascent: CGFloat = 0
    let descent: CGFloat = 0
    var width: CGFloat = 0
    let line: CTLineRef = CTLineCreateWithAttributedString(asp)

    width = CTLineGetTypographicBounds(line, &ascent, &descent, nil)

    // ...
}

但是我在这行中遇到&ascent的错误：

width = CTLineGetTypographicBounds(line, &ascent, &descent, nil)

＆＃39;＆安培;＆＃39;用于类型＆＃39; UnsafeMutablePointer＆＃39;
的非inout参数

Xcode建议我通过删除&来修复它。但是，当我这样做时，我收到了错误

无法转换类型＆＃39; CGFloat＆＃39;预期参数类型＆＃39; UnsafeMutablePointer＆＃39;

Interacting with C APIs documentation使用&语法，因此我不知道问题所在。如何解决此错误？

Answer 1

ascent和descent必须是变量才能传递作为&的进出参数：

var ascent: CGFloat = 0
var descent: CGFloat = 0
let line: CTLineRef = CTLineCreateWithAttributedString(asp)
let width = CGFloat(CTLineGetTypographicBounds(line, &ascent, &descent, nil))

从CTLineGetTypographicBounds()返回时，这些变量将设置为线的上升和下降。另请注意，此函数返回 Double，因此您需要将其转换为CGFloat。

斯威夫特错误：＆＃39;＆amp;＆＃39;用于类型＆＃39; UnsafeMutablePointer＆＃39;的非inout参数

1 个答案: