轉換對象 - 斯威夫特

Question

試圖重寫drawPlaceholderInRect在Swift2.1讓我改變文字顏色，我有一個很難以下的OBJ-C轉換到斯威夫特：

(void)drawPlaceholderInRect:(CGRect)rect 
{ 
    UIColor *colour = [UIColor whiteColor]; 

    if ([self.placeholder respondsToSelector:@selector(drawInRect:withAttributes:)]) { 

    NSDictionary *attributes = @{NSForegroundColorAttributeName: colour, NSFontAttributeName: self.font}; 
    CGRect boundingRect = [self.placeholder boundingRectWithSize:rect.size options:0 attributes:attributes context:nil]; 
    [self.placeholder drawAtPoint:CGPointMake(0, (rect.size.height/2)-boundingRect.size.height/2) withAttributes:attributes]; 
} 

我得到這個：

public override func drawPlaceholderInRect(rect: CGRect) { 
    let textDict: NSDictionary = [NSForegroundColorAttributeName: UIColor.whiteColor()] 

    ... 
    .. 
    . 
} 

有人可以幫忙嗎？

Answer 1

看看這是有益的：

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/index.html#//apple_ref/doc/uid/TP40014216-CH2-ID0

另外，如果你有麻煩翻譯Objective-C的斯威夫特，這可能會非常棘手，有時是重寫的方法在派生Objective-C類和然後在Swift中使用這個類。

Answer 2

func drawPlaceholder(in rect: CGRect) { 

    let colour: UIColor? = UIColor.white 

    if placeholder.responds(to: Selector("drawInRect:withAttributes:")) { 

     let attributes = [NSForegroundColorAttributeName: colour, NSFontAttributeName: font] 

     let boundingRect: CGRect = placeholder.boundingRect(with: rect.size, options: [], attributes: attributes, context: nil) 

     placeholder.draw(at: CGPoint(x: 0, y: (rect.size.height/2) - boundingRect.size.height/2), withAttributes: attributes) 
    } 
}