处理UILabel根据文字长度和大小自动适应宽度和高度

   //这个frame是初设的，没关系，后面还会重新设置其size。      UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0,0,0,0)];      label.numberOfLines = 0;      label.backgroundColor = [UIColor clearColor];             NSDictionary *attributes = @{NSFontAttributeName:[UIFont systemFontOfSize:20],};             NSString *str = @"abcdefg你上课可是你的拿到了";      CGSize textSize = [str boundingRectWithSize:CGSizeMake(100, 100) options:NSStringDrawingTruncatesLastVisibleLine attributes:attributes context:nil].size;;             [label setFrame:CGRectMake(100, 100, textSize.width, textSize.height)];      label.textColor = [UIColor greenColor];      label.text = str;      [self.view addSubview:label];