I am wondering if there is a special method/trick to check if a String object is null. I know about the String.IsNullOrEmpty method but I want to differentiate a null String from an empty String (="").
Should I simply use:
if (s == null) {
// blah blah...
}
...or is there another way?
An object can't be null - the value of an expression can be null. It's worth making the difference clear in your mind. The value of s isn't an object - it's a reference, which is either null or refers to an object.
And yes, you should just use
if (s == null)
Note that this will still use the overloaded == operator defined in string, but that will do the right thing.
You can use the null coalescing double question marks to test for nulls in a string or other nullable value type:
textBox1.Text = s ?? "Is null";
The operator '??' asks if the value of 's' is null and if not it returns 's'; if it is null it returns the value on the right of the operator.
More info here: https://msdn.microsoft.com/en-us/library/ms173224.aspx
And also worth noting there's a null-conditional operator ?. and ?[ introduced in C# 6.0 (and VB) in VS2015
textBox1.Text = customer?.orders?[0].description ?? "n/a";
This returns "n/a" if description is null, or if the order is null, or if the customer is null, else it returns the value of description.
More info here: https://msdn.microsoft.com/en-us/library/dn986595.aspx
To be sure, you should use a function to check for null and empty as below:
string str = ...
if (!String.IsNullOrEmpty(str))
{
...
}
If you are using C# 7.0 or above you can use is null:
if (s is null) {
// blah blah...
}
Also, note that when working with strings you might consider also using IsNullOrWhiteSpace that will also validate that the string doesn't contain only spaces.
For .net 5 (probably also for .net Core 3.1)
Different possibility to write but always the same problem.
string wep = test ?? "replace";
Console.WriteLine(wep);
result: "replace"
or
string test=null;
test ??= "replace";
Console.WriteLine(test);
test="";
test??="replace";
Console.WriteLine(test);
string test="";
if(test is null)
Console.WriteLine("yaouh");
else
Console.WriteLine("Not yahouu");
Result: "Not yahou"
object is null is available since C# 7 specification.