iOS UILabel计算宽度和高度

1、根据文本计算size，这里需要传入attributes

    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(20, 100, 0, 0)];
    label.text = @"12331afaa我是谁的谁";
    label.textColor = [UIColor redColor];
    label.backgroundColor = [UIColor greenColor];
    label.font = [UIFont systemFontOfSize:20];
    [self.view addSubview:label];

    CGSize size = [label.text sizeWithAttributes:@{NSFontAttributeName:label.font}];
    label.frame = CGRectMake(20, 100, size.width, size.height);
    // 193.482031    heigth:23.867188

2、富文本计算size

    CGSize size = [label.attributedText size];
    label.frame = CGRectMake(20, 100, size.width, size.height);
    // 193.482031    heigth:23.867188

3、通过UIView的 sizeThatFits

    // 在单行文本的情况下，参数size设置多少都无所谓，所以里传了CGSizeZero
    CGSize size = [label sizeThatFits:CGSizeZero];
    label.frame = CGRectMake(20, 100, size.width, size.height);
    // 193.500000    heigth:24.000000
    
    // 可用此方法计算高度
    label.text = @"ABCDEFGHIJKLMN";
    label.numberOfLines = 0;
    label.textAlignment = NSTextAlignmentCenter;
    CGSize size = [label sizeThatFits:CGSizeMake(15, 0)];
    label.frame = CGRectMake(20, 100, size.width, size.height);
    // 15.000000    heigth:334.500000