Question

The program does similar things again and again. I want to reduce the code I use.
It’s an example, in this example it is not needed but I will do another thing similar in the future. Now I’m confused and said “Why should I copy the same codes one by one?”

But I get ‘Object’ does not contain a definition for ‘ComputeHash’ error. In runtime they won’t be objects, they are classes. So they don’t have the same variable type. What should I do?

private void button1_Click(object sender, EventArgs e)
{
    OpenFileDialog op = new OpenFileDialog();
    op.Filter = "ALL files(*.*)|*.*";
    if (op.ShowDialog() == DialogResult.OK)
    {
        textBox1.Text = String.Empty;
        var list = new ArrayList() { crc32, md5, sha1 };
        foreach (var checksum in list)
        {
            using (FileStream fs = File.Open(op.FileName, FileMode.Open))
            {
                foreach (byte b in checksum.ComputeHash(fs))
                {
                    hash += b.ToString("x2").ToLower();
                }
                textBox1.Text += hash + "\r\n";
                hash = String.Empty;
            }
        }
    }
}

Answer 1

It’s because you’re using the non-generic ArrayList type. If you change it to:

var list = new List<HashAlgorithm> { crc32, md5, sha1, ... };

it’ll be fine. Basically, the compile-time type of checksum is currently object, not HashAlgorithm.

You should use strongly typed collections whenever you can.

(You should also use using statements for streams – currently you’re not closing the stream.)