Null in asp net

But at the same time, you have to show the view of the address because the admin user could enter the address at any time. Having models that can possibly be null creates some complications in ASP.

I found myself running into a specific situation, Perhaps others have too? I'll assume you are pretty familiar with ASP. So let me describe the scenario. I have an admin screen where I am editing the information for Personnel. There are input elements for first name, last name, street address, etc. So let's say I have 2 domain models as such. The code shown is way simplified. Realize that there is a one to one relationship between Person and Address , and that Person.

AddressId is nullable. I won't show the code but, let's say there is some mechanism entity framework or whatever to retrieve an instance of a Personnel object by ID. The key thing to realize is that it is possible for the Address property of Personnel to be null because not all personnel had their address information entered and so there will be no record in the database for it.

Here's where it gets weird. The UI or View still needs to still show the input elements for the address model because at any time the admin user can then just put in the person's address OR they can leave it blank if they don't intend to provide address information. So Address may be null but yet the UI input elements still need to be present in the page. I have a partial view that is used for the Address Type which looks something like this:. Assume I put all this into a controller and view and request the URL for the personnel admin page for an employee that had no address.

It might look something like this:. OK, so what's the problem with this? If I view the source of the page and look at the markup in the Address section, I see this:. The value of the hidden input is null or really a blank string. You get a null return value from a method, and then call a method on the returned type. This sometimes is the result of a documentation error; the documentation fails to note that a method call can return null. In other cases, your code erroneously assumes that the method will always return a non- null value.

The code in the following example assumes that the Array. Find method always returns Person object whose FirstName field matches a search string. Because there is no match, the runtime throws a NullReferenceException exception. To address this problem, test the method's return value to ensure that it is not null before calling any of its members, as the following example does.

You're using an expression for example, you're chaining a list of methods or properties together to retrieve a value and, although you're checking whether the value is null , the runtime still throws a NullReferenceException exception. This occurs because one of the intermediate values in the expression returns null.

As a result, your test for null is never evaluated. The following example defines a Pages object that caches information about web pages, which are presented by Page objects. The Example. Main method checks whether the current web page has a non-null title and, if it does, displays the title.

Despite this check, however, the method throws a NullReferenceException exception. The exception is thrown because pages. CurrentPage returns null if no page information is stored in the cache.

This exception can be corrected by testing the value of the CurrentPage property before retrieving the current Page object's Title property, as the following example does:.

You're enumerating the elements of an array that contains reference types, and your attempt to process one of the elements throws a NullReferenceException exception. The following example defines a string array. A for statement enumerates the elements in the array and calls each string's Trim method before displaying the string.

This exception occurs if you assume that each element of the array must contain a non-null value, and the value of the array element is in fact null. The exception can be eliminated by testing whether the element is null before performing any operation on that element, as the following example shows. A NullReferenceException exception is thrown by a method that is passed null. Some methods validate the arguments that are passed to them. If they do and one of the arguments is null , the method throws an System.

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