Application crash after detect null variable

Question

I have a TreeView where I want to get NextNode so I do simple like:

var nextNode = e.Node.NextNode.Text;

If it have nextNode it returns value right. Problem if it comes null, application crash and throw

System.NullReferenceException: 'Object reference not set to an instance of an object.'

System.Windows.Forms.TreeNode.NextNode.get returned null.

Why application crash? should not return the null variable instead application crash?

You can't use the Text property if NextNode is null. Check first. — LarsTech, Oct 04 '18 at 23:14

score 3 · Answer 1 · answered Oct 04 '18 at 23:17

It appears that an instance of NextNode does not exist yet you attempt to access the Text property.

You have two options:

Retrieve the NextNode object and check for NULL
Use the null coalescing operator to access the text or substitute it.

1 - Check for null

NextNode node = e.Node.NextNode;
string thetext = string.Empty;
if (node != null)
    thetext = node.Text

2 - Null coalescing operator

string thetext = e.Node?.NextNode?.Text ?? string.Empty;

They will both do the same thing. If NextNode is null then the variable thetext will contain an empty string, otherwise it will contain the Text of NextNode.

Application crash after detect null variable

1 Answers1

1 - Check for null

2 - Null coalescing operator