C#自定义类型强制转换 C#自定义类型强制转换实例分析

public class MyCurrency
{
  public uint Dollars;
  public ushort Cents;
  public MyCurrency(uint dollars, ushort cents)
  {
    this.Dollars = dollars;
    this.Cents = cents;
  }
  public override string ToString()
  {
    return string.Format(
      "${0}.{1}", Dollars, Cents
    );
  }
  //提供MyCurrency到float的隐式转换
  public static implicit operator float(MyCurrency value)
  {
    return value.Dollars + (value.Cents / 100.0f);
  }
  //把float转换为MyCurrency,不能保证转换肯定成功,因为float可以
  //存储负值,而MyCurrency只能存储正数
  //float存储的数量级比uint大的多，如果float包含一个比unit大的值，
  //将会得到意想不到的结果，所以必须定义为显式转换
  //float到MyCurrency的显示转换
  public static explicit operator MyCurrency(float value)
  {
    //checked必须加在此处，加在调用函数外面是不会报错的，
    //因为溢出的异常是在强制转换运算符的代码中发生的
    //Convert.ToUInt16是为了防止丢失精度
    //该段内容很重要，详细参考"C#高级编程(中文第七版) 218页说明"
    checked
    {
      uint dollars = (uint)value;
      ushort cents = Convert.ToUInt16((value - dollars) * 100);
      return new MyCurrency(dollars, cents);
    }
  }
}

private void btn_测试自定义类型强制转换_Click(object sender, EventArgs e)
{
  MyCurrency tmp = new MyCurrency(10, 20);
  //调用MyCurrency到float的隐式转换
  float fTmp = tmp;
  MessageBox.Show(fTmp.ToString());
  float fTmp2 = 200.30f;
  //调用float到MyCurrency的显示转换
  MyCurrency tmp2 = (MyCurrency)fTmp2;
  MessageBox.Show(tmp2.ToString());
}