C#•4mo ago

✅ Library is a null value

Hello, I am currently making a library application using Winforms. However, I am currently facing the issue of getting a null value for my library whenever I try to add a book. Can someone tell me what the issue with my code is? Github: https://github.com/Allen620-arc/LibraryManagementSystem

GitHub

GitHub - Allen620-arc/LibraryManagementSystem

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16 Replies

Angius•4mo ago

That's a lot of files and a lot of lines of code Where does the error happen?

Gamer1234556OP•4mo ago

Well there are a lot of places where that error happens For example: When pressing Add Books button, filling out the form and pressing save, I get an error at line 26 saying: System.NullReferenceException: 'Object reference not set to an instance of an object.' library was null. This is in the AddBooks.cs file btw

Angius•4mo ago

There's no such file in the repo Did you mean AddBookForm.cs?

Gamer1234556OP•4mo ago

Yeah sorry

Angius•4mo ago

Well, that would mean that either the constructor is not called, or the constructor itself gets a null passed to it It seems to be called from LibraryForm And I don't see the library field being initialized anywhere in there So, that's your null

Gamer1234556OP•4mo ago

You mean in the LibraryForm? I initialized it in line 15 there

Angius•4mo ago

No, you did not

Angius•4mo ago

Angius•4mo ago

You created a field library of type Library and left it uninitialized

MODiX•4mo ago

Angius

REPL Result: Failure

class Bar
{
    public string Name => nameof(Bar);
}
class Foo
{
    private Bar _bar;

    public void Check()
        => Console.WriteLine($"Bar {(_bar is null ? "is" : "is not")} null");

    public void SayIt()
        => Console.WriteLine($"Bar is named {_bar.Name}");
}

var f = new Foo();
f.Check();
f.SayIt();

class Bar
{
    public string Name => nameof(Bar);
}
class Foo
{
    private Bar _bar;

    public void Check()
        => Console.WriteLine($"Bar {(_bar is null ? "is" : "is not")} null");

    public void SayIt()
        => Console.WriteLine($"Bar is named {_bar.Name}");
}

var f = new Foo();
f.Check();
f.SayIt();

Console Output

Bar is null

Bar is null

Exception: NullReferenceException

- Object reference not set to an instance of an object.

- Object reference not set to an instance of an object.

Compile: 536.248ms | Execution: 44.995ms | React with ❌ to remove this embed.

Angius•4mo ago

You said "this is a box for apples" and did not put any apples in it

Gamer1234556OP•4mo ago

Ok yeah I fixed the error Thanks I didn't know how I missed that How do I close post again?

Angius•4mo ago

$close

MODiX•4mo ago

If you have no further questions, please use /close to mark the forum thread as answered

Gamer1234556OP•4mo ago

$close

MODiX•4mo ago

If you have no further questions, please use /close to mark the forum thread as answered

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✅ Library is a null value