Check if dictionary value of key is null

Question

I try to use a Dictionary and need to Check if the Value of a Key (called Name) is empty and if so, then use some default string as Value for my Key as, something like "unknown".

I know I can check a string for example with string.Length == 0 but my problem here is that I have an object as value and its hard for me to catch it.

Thats my code:

 IDictionary<string, object> parameters = new Dictionary<string, object>();
 string Name = de.Properties["Name"].Value.ToString(); //Name is sometimes empty and sometimes not
 parameters.Add("Name", Name);

Update:

IDictionary<string, object> parameters = new Dictionary<string, object>();
string Name = de.Properties["Name"].Value.ToString();
 if (parameters.TryGetValue("Name", out var Name))
    {
      parameters.Add("Name", Name ?? "unknown");
    }

Solution 1

You can try to use ContainsKey method to check that Name key is exist in dictionary. Then get an actual string value by checking for null using null-conditional ?. operator. If the result is null or empty string, you'll set the name to unknown value

if (de.Properties.ContainsKey("Name"))
{
    var name = de.Properties["Name"]?.ToString();
    if (string.IsNullOrEmpty(name))
    {
        name = "unknown";
    }
}

Solution 2

null and an empty string are completely different things. null means there's no value, while an empty string is a string, it's just empty. You can't call .ToString() or .Length on a null, you'd get an exception precisely because there's no value to handle that call.

You can use Dictionary.TryGetValue to check for existence and retrieve the value at the same time.

After that, if you really want to convert everything to a string, you can use the null-conditional operator ?. to call ToString() without throwing if name is null. If name is null, the entire expression name?.ToString() evaluates to null too.

You can then use the null-coalescing operator ?? to replace nulls with a default value :

var de= new Dictionary<string, object?>();
de["Name1"]=null;
de["Name2"]=42;

if(de.TryGetValue("Name2",out var name))
{
    var valueAsString=name?.ToString() ;
    parameters.Add("Name2", valueAsString ?? "unknown");
}

If you just want to replace nulls with a default value, you don't need ToString() :

if(de.TryGetValue("Name2",out var name))
{
    parameters.Add("Name2", name ?? "unknown");
}

If you want to check for null or empty, you can use String.IsNullOrEmpty :

if(de.TryGetValue("Name2",out var name))
{
    var newValue=String.IsNullOrEmpty(name) 
                       ? "unknown" 
                       : name.ToString();  //Only if we want to format to strings
    parameters.Add("Name2", newValue);
}

Finally, if you want to replace existing keys in the parameters dictionary, use

parameters["Name2]= newValue;