iOS UILabel根据字符串长度自动适应宽度和高度

    UILabel *label = [[UILabel alloc] init];
    label.text  = @"这是用于测试的文字"
    label.numberOfLines = 0;
    
    NSDictionary *attributes = @{NSFontAttributeName:[UIFont systemFontOfSize:20],};
    CGSize textSize = [label.text boundingRectWithSize:CGSizeMake(100, 100) options:NSStringDrawingTruncatesLastVisibleLine attributes:attributes context:nil].size;;
    
    [label setFrame:CGRectMake(100, 100, textSize.width, textSize.height)];