How to compare IFormatProvider?

Question

I have an Grid UserControl. It used IFormatProvider to format Text in a Cell for display. Each Cell allows to set own IFormatProvider. On request of cell's DisplayText, program calls Cell's IFormatProvider, then Column's IFormatProvider in order. I make an array to save all non-identical IFormatProvider so that I just need to save ID to retrieve the format.

How to compare the IFormatProvider? If they are different, save into the array.

private IFormatProvider[] FormatProviders;

internal short CreateNewFormatProviders(IFormatProvider newFormatProvider)
{
    if (newFormatProvider == null) // (IFormatProvider.Equals(newFormatProvider,null))
    {
        return -1;
    }
    int len = this.FormatProviders.Length;
    for (int i = 0; i < len; i++)
    {
        if (IFormatProvider.Equals(this.FormatProviders[i],newFormatProvider))
        {
            return (short)i;
        }
    }
    Array.Resize<IFormatProvider>(ref this.FormatProviders, len + 1);
    this.FormatProviders[len] = newFormatProvider;
    return (short)len;
}

In above code, I used IFormatProvider.Equals. Is it functioning or has better way?

`IFormatProvider` does not have concept of "name"... So not exactly clear what you plan to compare (obviously you've already confirmed that most `ToString` calls return the same value for types in question, so I assume the code in the post is just an example what you'd like to do) — Alexei Levenkov, May 09 '19 at 06:35
While [edit] post to clarify first question I'd recommend to remove the second one completely (as you've searched for it already and found stuff like https://stackoverflow.com/questions/605621/how-to-get-object-size-in-memory) - otherwise post will be considered "too broad" and closed (plus post could be downvted as you did not show results of you search for https://www.bing.com/search?q=c%23+size+of+object+in+memory). — Alexei Levenkov, May 09 '19 at 06:37
From what I tested, IFormatProvider.Equals doesn't work.IFormatProvider newfmt = new CustomFormatProvider(); IFormatProvider newfmt2 = new CustomFormatProvider();Console.WriteLine(object.Equals(newfmt, newfmt2)); Console.WriteLine(IFormatProvider.Equals(newfmt, newfmt2)); Console.WriteLine(newfmt == newfmt2);all return False. — qtg, May 09 '19 at 07:55
object.ToString() returns the name of my custom IFormatProvider which can identify what interface is being used. — qtg, May 09 '19 at 08:13

score 0 · Accepted Answer · edited May 10 '19 at 05:20

Note: All types that I have for IFormatProvider are custom and implement .ToString that return unique values. If this is not the case for you this approach will not work.

After debug, I used .ToString() to check whether duplicated.

private IFormatProvider[] FormatProviders = new IFormatProvider[1];
internal short CreateNewFormatProviders(IFormatProvider newFormatProvider)
    {             
        if (newFormatProvider == null) // (IFormatProvider.Equals(newFormatProvider,null))
        {
            return -1;
        }

        if (this.FormatProviders[0] == null)
        {
            this.FormatProviders[0] = newFormatProvider;
            return 0;
        }

        int len = this.FormatProviders.Length;
        for (int i = 0; i < len; i++)
        {
            //if (IFormatProvider.Equals(this.FormatProviders[i],newFormatProvider)) *always return False*
            if (newFormatProvider.ToString() == this.FormatProviders[i].ToString()) 
            {
                return (short)i;
            }
        }
        Array.Resize<IFormatProvider>(ref this.FormatProviders, len + 1);
        this.FormatProviders[len] = newFormatProvider;
        return (short)len;
    }

testing code:

   IFormatProvider newfmt1 = new CustomFormatProvider1();
   IFormatProvider newfmt1_ = new CustomFormatProvider1();
   IFormatProvider newfmt2 = new CustomFormatProvider2();
   short index_newfmt1 = CreateNewFormatProviders(newfmt1);
   short index_newfmt1_= CreateNewFormatProviders(newfmt1_);
   short index_newfmt2= CreateNewFormatProviders(newfmt2);

Result is as I expect:

      index_newfmt1 = 0
      index_newfmt1_ = 0
      index_newfmt2 = 1

How to compare IFormatProvider?

1 Answers1