在 Cocoa View 中绘制居中对齐的文本

Question

我正在尝试在中心对齐的可可 NSView 中绘制一个带有新行 (\n) 的字符串。例如，如果我的字符串是：

NSString * str = @"this is a long line \n and \n this is also a long line"; 

我希望这看起来有点像：

  this is a long line
         and
this is also a long line

这是我在 NSView drawRect 方法中的代码：

NSMutableParagraphStyle * paragraphStyle = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];

[paragraphStyle setAlignment:NSCenterTextAlignment];

NSDictionary * attributes = [NSDictionary dictionaryWithObject:paragraphStyle forKey:NSParagraphStyleAttributeName];

NSString * mystr = @"this is a long line \n and \n this is also a long line";

[mystr drawAtPoint:NSMakePoint(20, 20) withAttributes:attributes];

它仍然以左对齐方式绘制文本。这段代码有什么问题？

Answer 1

-[NSString drawAtPoint:withAttributes:] 的文档说明如下：

渲染区域的宽度（垂直布局的高度）是无限的，不像drawInRect:withAttributes:，它使用一个边界矩形。因此，此方法将文本呈现在一行中。

由于宽度是无限的，该方法会丢弃段落对齐并始终呈现字符串左对齐。

您应该改用-[NSString drawInRect:withAttributes:]。因为它接受一个框架并且一个框架有一个宽度，所以它可以计算中心对齐。例如：

NSMutableParagraphStyle * paragraphStyle =
    [[[NSParagraphStyle defaultParagraphStyle] mutableCopy] autorelease];
[paragraphStyle setAlignment:NSCenterTextAlignment];
NSDictionary * attributes = [NSDictionary dictionaryWithObject:paragraphStyle
    forKey:NSParagraphStyleAttributeName];

NSString * mystr = @"this is a long line \n and \n this is also a long line";    
NSRect strFrame = { { 20, 20 }, { 200, 200 } };

[mystr drawInRect:strFrame withAttributes:attributes];

请注意，您在原始代码中泄漏了 paragraphStyle。