UILabel實現文本自適應方法（ios7）

- (void)initUserInterface
{
    UILabel *label = [[UILabel alloc]init];
    label.numberOfLines = 0; // 需要把顯示行數設置成無限制
    label.font = [UIFont systemFontOfSize:15];
    label.textAlignment = NSTextAlignmentCenter;
    label.text = @"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
    CGSize size =  [self sizeWithString:label.text font:label.font];
    label.bounds = CGRectMake(0, 0, size.width, size.height);
    label.center = self.view.center;
    [self.view addSubview:label];
    
}
// 定義成方法方便多個label調用 增加代碼的復用性
- (CGSize)sizeWithString:(NSString *)string font:(UIFont *)font
{
    CGRect rect = [string boundingRectWithSize:CGSizeMake(320, 8000)//限制最大的寬度和高度
                                       options:NSStringDrawingTruncatesLastVisibleLine | NSStringDrawingUsesFontLeading  |NSStringDrawingUsesLineFragmentOrigin//采用換行模式
                                    attributes:@{NSFontAttributeName: font}//傳人的字體字典
                                       context:nil];
    
    return rect.size;
}