根据字体数量和字体的型号 动态计算Label的高度

 NSString *text = @"askdasfniuqwehnfunujgbnuyqbafyuhgbyusadfhbgvyhwreqwf";

   

    

    _myLabel=[[UILabel alloc] initWithFrame:CGRectMake(0, 23, 175, 33)];

    [_myLabel setFont:[UIFont fontWithName:@"Helvetica" size:30]];

    [_myLabel setNumberOfLines:0];

    [_myLabel setBackgroundColor:[UIColor clearColor]];

    [self.view addSubview:_myLabel];

    _myLabel.backgroundColor = [UIColor redColor];

//    UIFont *font = [UIFont fontWithName:@"Helvetica" size:30];//必须和Label的字体型号保持一致

    UIFont *font = [UIFont systemFontOfSize:30];

    CGSize size = CGSizeMake(320,2000); //设置一个行高上限

   

    NSDictionary * tdic = [NSDictionary dictionaryWithObjectsAndKeys:font, NSFontAttributeName,nil];

    

    size =[text boundingRectWithSize:size options:NSStringDrawingUsesLineFragmentOrigin |NSStringDrawingUsesFontLeading attributes:tdic context:nil].size;

    CGRect rect=_myLabel.frame;

    rect.size=size;

    [_myLabel setFrame:rect];

    [_myLabel setText:text];

    NSLog(@"%f--%f",_myLabel.frame.size.width,_myLabel.frame.size.height);