What is the best way to dump entire objects to a log in C#?

You could base something on the ObjectDumper code that ships with the Linq samples.
Have also a look at the answer of this related question to get a sample.

I'm certain there are better ways of doing this, but I have in the past used a method something like the following to serialize an object into a string that I can log:

  private string ObjectToXml(object output)
  {
     string objectAsXmlString;

     System.Xml.Serialization.XmlSerializer xs = new System.Xml.Serialization.XmlSerializer(output.GetType());
     using (System.IO.StringWriter sw = new System.IO.StringWriter())
     {
        try
        {
           xs.Serialize(sw, output);
           objectAsXmlString = sw.ToString();
        }
        catch (Exception ex)
        {
           objectAsXmlString = ex.ToString();
        }
     }

     return objectAsXmlString;
  }

You'll see that the method might also return the exception rather than the serialized object, so you'll want to ensure that the objects you want to log are serializable.

You could use reflection and loop through all the object properties, then get their values and save them to the log. The formatting is really trivial (you could use \t to indent an objects properties and its values):

MyObject
    Property1 = value
    Property2 = value2
    OtherObject
       OtherProperty = value ...

What I like doing is overriding ToString() so that I get more useful output beyond the type name. This is handy in the debugger, you can see the information you want about an object without needing to expand it.

All of the paths above assume that your objects are serializable to XML or JSON,
or you must implement your own solution.

But in the end you still get to the point where you have to solve problems like

• recursion in objects
• non-serializable objects
• exceptions
• ...

Plus log you want more information:

• when the event happened
• callstack
• which threead
• what was in the web session
• which ip address
• url
• ...

There is the best solution that solves all of this and much more.
Use this Nuget package: Desharp.
For all types of applications - both web and desktop applications.
See it's Desharp Github documentation. It has many configuration options.

Just call anywhere:

Desharp.Debug.Log(anyException);
Desharp.Debug.Log(anyCustomValueObject);
Desharp.Debug.Log(anyNonserializableObject);
Desharp.Debug.Log(anyFunc);
Desharp.Debug.Log(anyFunc, Desharp.Level.EMERGENCY); // you can store into different files

• it can save the log in nice HTML (or in TEXT format, configurable)
• it's possible to write optionally in background thread (configurable)
• it has options for max objects depth and max strings length (configurable)
• it uses loops for iteratable objects and backward reflection for everything else,
  indeed for anything you can find in .NET environment.

I believe it will help.

Based on @engineforce answer, I made this class that I'm using in a PCL project of a Xamarin Solution:

/// <summary>
/// Based on: https://stackoverflow.com/a/42264037/6155481
/// </summary>
public class ObjectDumper
{
    public static string Dump(object obj)
    {
        return new ObjectDumper().DumpObject(obj);
    }

    StringBuilder _dumpBuilder = new StringBuilder();

    string DumpObject(object obj)
    {
        DumpObject(obj, 0);
        return _dumpBuilder.ToString();
    }

    void DumpObject(object obj, int nestingLevel)
    {
        var nestingSpaces = "".PadLeft(nestingLevel * 4);

        if (obj == null)
        {
            _dumpBuilder.AppendFormat("{0}null\n", nestingSpaces);
        }
        else if (obj is string || obj.GetType().GetTypeInfo().IsPrimitive || obj.GetType().GetTypeInfo().IsEnum)
        {
            _dumpBuilder.AppendFormat("{0}{1}\n", nestingSpaces, obj);
        }
        else if (ImplementsDictionary(obj.GetType()))
        {
            using (var e = ((dynamic)obj).GetEnumerator())
            {
                var enumerator = (IEnumerator)e;
                while (enumerator.MoveNext())
                {
                    dynamic p = enumerator.Current;

                    var key = p.Key;
                    var value = p.Value;
                    _dumpBuilder.AppendFormat("{0}{1} ({2})\n", nestingSpaces, key, value != null ? value.GetType().ToString() : "<null>");
                    DumpObject(value, nestingLevel + 1);
                }
            }
        }
        else if (obj is IEnumerable)
        {
            foreach (dynamic p in obj as IEnumerable)
            {
                DumpObject(p, nestingLevel);
            }
        }
        else
        {
            foreach (PropertyInfo descriptor in obj.GetType().GetRuntimeProperties())
            {
                string name = descriptor.Name;
                object value = descriptor.GetValue(obj);

                _dumpBuilder.AppendFormat("{0}{1} ({2})\n", nestingSpaces, name, value != null ? value.GetType().ToString() : "<null>");

                // TODO: Prevent recursion due to circular reference
                if (name == "Self" && HasBaseType(obj.GetType(), "NSObject"))
                {
                    // In ObjC I need to break the recursion when I find the Self property
                    // otherwise it will be an infinite recursion
                    Console.WriteLine($"Found Self! {obj.GetType()}");
                }
                else
                {
                    DumpObject(value, nestingLevel + 1);
                }
            }
        }
    }

    bool HasBaseType(Type type, string baseTypeName)
    {
        if (type == null) return false;

        string typeName = type.Name;

        if (baseTypeName == typeName) return true;

        return HasBaseType(type.GetTypeInfo().BaseType, baseTypeName);
    }

    bool ImplementsDictionary(Type t)
    {
        return t is IDictionary;
    }
}

So far a simplest and tidiest way for me is a serializer from YamlDotNet package.

using YamlDotNet.Serialization;

List<string> strings=new List<string>{"a","b","c"};
new Serializer().Serialize(strings)

will give you

- a
- b
- c

A more comprehensive example is here https://dotnetfiddle.net/KuV63n

Today you don't even need an external dependency. You can just use the built-in Microsoft Json Serializer.

using System;
using System.Text.Json;

namespace MyCompany.Core.Extensions
{
    public static class ObjectExtensions
    {
        public static string Dump(this object obj)
        {
            try
            {
                return JsonSerializer.Serialize(obj);
            }
            catch(Exception)
            {
                return string.Empty;
            }
        }
    }
}

Notice that you can pass a JsonSerializerOptions parameter to further customize the serialization to your liking:

Let's say you want to write the JSON indented for easy reading... we'd use:

   new JsonSerializerOptions { WriteIndented = true }

#######

Here's a good guide if you wish to migrate from NewtonSoft.Json to System.Text.Json:

Compare Newtonsoft.Json to System.Text.Json, and migrate to System.Text.Json