[c#] Get a specific bit from byte

I have a byte, specifically one byte from a byte array which came in via UDP sent from another device. This byte stores the on/off state of 8 relays in the device.

How do I get the value of a specific bit in said byte? Ideally an extension method would look the most elegant and returning a bool would make the most sense to me.

public static bool GetBit(this byte b, int bitNumber)
{
    //black magic goes here
}

try this:

return (b & (1 << bitNumber))>0;

Try the code below. The difference with other posts is that you can set/get multiple bits using a mask (field). The mask for the 4th bit can be 1<<3, or 0x10, for example.

    public int SetBits(this int target, int field, bool value)
    {
        if (value) //set value
        {
            return target | field;
        }
        else //clear value
        {
            return target & (~field);
        }
    }

    public bool GetBits(this int target, int field)
    {
        return (target & field) > 0;
    }

** Example **

        bool is_ok = 0x01AF.GetBits(0x10); //false
        int res = 0x01AF.SetBits(0x10, true);
        is_ok = res.GetBits(0x10);  // true

[Flags]
enum Relays : byte
{
    relay0 = 1 << 0,
    relay1 = 1 << 1,
    relay2 = 1 << 2,
    relay3 = 1 << 3,
    relay4 = 1 << 4,
    relay5 = 1 << 5,
    relay6 = 1 << 6,
    relay7 = 1 << 7
}

public static bool GetRelay(byte b, Relays relay)
{
    return (Relays)b.HasFlag(relay);
}

This

public static bool GetBit(this byte b, int bitNumber) {
   return (b & (1 << bitNumber)) != 0;
}

should do it, I think.

Using BitArray class and making an extension method as OP suggests:

public static bool GetBit(this byte b, int bitNumber)
{
    System.Collections.BitArray ba = new BitArray(new byte[]{b});
    return ba.Get(bitNumber);
}

another way of doing it :)

return ((b >> bitNumber) & 1) != 0;

The method is to use another byte along with a bitwise AND to mask out the target bit.

I used convention from my classes here where "0" is the most significant bit and "7" is the least.

public static class ByteExtensions
{
    // Assume 0 is the MSB andd 7 is the LSB.
    public static bool GetBit(this byte byt, int index)
    {
        if (index < 0 || index > 7)
            throw new ArgumentOutOfRangeException();

        int shift = 7 - index;

        // Get a single bit in the proper position.
        byte bitMask = (byte)(1 << shift);

        // Mask out the appropriate bit.
        byte masked = (byte)(byt & bitMask);

        // If masked != 0, then the masked out bit is 1.
        // Otherwise, masked will be 0.
        return masked != 0;
    }
}

This is works faster than 0.1 milliseconds.

return (b >> bitNumber) & 1;

While it's good to read and understand Josh's answer, you'll probably be happier using the class Microsoft provided for this purpose: System.Collections.BitArray It's available in all versions of .NET Framework.