CODEWITHSUNDEEP
c#asp.net-mvc
Lasse Edsvik
Lasse Edsvik

Reputation: 9298

Empty string if null

I have this in my code:

SelectList(blah, "blah", "blah", cu.Customer.CustomerID.ToString())

It gives a error when it returns null, how can I make it CustomerID is an empty string if it is null?

/M

Upvotes: 47

Views: 142851

Answers (4)

Dima Korobskiy
Dima Korobskiy

Reputation: 1556

(C# 2.0 - C# 5.0)

The ternary operator works, but if you want even shorter expression working on arbitrary objects you can use:

(myObject ?? "").ToString()

Here is real-life example from my code:

 private HtmlTableCell CreateTableCell(object cellContents)
 {
     return new HtmlTableCell()
     {
         InnerText = (cellContents ?? "").ToString()             
     };
 }

Upvotes: 29

vgru
vgru

Reputation: 51204

(Update for C# 6.0)

If you are using C# 6 or newer (Visual Studio 2015 or newer), then you can achieve this using the null-conditional operator ?.:

var customerId = cu.Customer?.CustomerId.ToString() ?? "";

One useful property of the null-conditional operator is that it can also be "chained" if you want to test if several nested properties are null:

// ensure (a != null) && (b != null) && (c != null) before invoking
// a.b.c.CustomerId, otherwise return "" (short circuited at first encountered null)
var customerId = a?.b?.c?.CustomerId.ToString() ?? "";

For C# versions prior to 6.0 (VS2013 or older), you could coalesce it like this:

string customerId = cu.Customer != null ? cu.Customer.CustomerID.ToString() : "";

Simply check if the object is non-null before you try to access its members, and return an empty string otherwise.

Apart from that, there are situations where null object pattern is useful. That would mean that you ensure that your Customer's parent class (type of cu in this case) always return an actual instance of an object, even if it is "Empty". Check this link for an example, if you think it may apply to your problem: How do I create a Null Object in C#.

Upvotes: 103

adrianbanks
adrianbanks

Reputation: 82934

It depends of the type of CustomerID.

If CustomerID is a string then you can use the null coalescing operator:

SelectList(blah, "blah", "blah", cu.Customer.CustomerID ?? string.Empty)

If CustomerID is a Nullable<T>, then you can use:

SelectList(blah, "blah", "blah", cu.Customer.CustomerID.ToString())

This will work because the ToString() method of Nullable<T> returns an empty string if the instance is null (technically if the HasValue property is false).

Upvotes: 17

Palantir
Palantir

Reputation: 24182

SelectList(blah, "blah", "blah", 
(cu.Customer.CustomerID!=null?cu.Customer.CustomerID.ToString():"")
)

Upvotes: 1

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