NSString 字体大小特定于框架宽度

我在用drawRect对于文本显示，调用NSString。我正在尝试使用sizeWithFont自动调整字体大小（缩小），默认字体大小为 17，如果不适合宽度大小，则使用循环将字体大小减小 1。谁能帮助我如何实现这个？现在的例子就很好了，我只是将字体大小设置为 17.0

[[self.string displayName] drawAtPoint:CGPointMake(xcoord, ycoord) withFont:[UIFont boldSystemFontOfSize:17.0]];
CGSize size = [[self.patient displayName] sizeWithFont:[UIFont boldSystemFontOfSize:17.0]];
max_current_y = size.height > max_current_y ? size.height : max_current_y;
xcoord = xcoord + 3.0f + size.width;

好吧，那算了。下面是同一方法的修改版本，该方法采用 NSString 返回字体：

    -(UIFont*)getFontForString:(NSString*)string
               toFitInRect:(CGRect)rect
                  seedFont:(UIFont*)seedFont{
    UIFont* returnFont = seedFont;
    CGSize stringSize = [string sizeWithAttributes:@{NSFontAttributeName : seedFont}];

    while(stringSize.width > rect.size.width){
        returnFont = [UIFont systemFontOfSize:returnFont.pointSize -1];
        stringSize = [string sizeWithAttributes:@{NSFontAttributeName : returnFont}];
    }

    return returnFont;
}

调用方法如下：

NSString* stringToDraw = @"Test 123";

    CGRect rect = CGRectMake(100., 100., 100., 200.);
    UIFont* font = [self getFontForString:stringToDraw toFitInRect:rect seedFont:[UIFont systemFontOfSize:20]];
    [stringToDraw drawInRect:rect withFont:font];

代码适用于 iOS7+