Dictionary KeyNotFoundException NOT giving error ... WHY?

Question

This question is not why it is giving an error .. rather why it is not giving an error ...

private void Form1_Load(object sender, EventArgs e)
{
    Dictionary<string, string> dic = new Dictionary<string, string>();
    dic["666bytes"] = "ME";
    MessageBox.Show(dic["should_give_error"]);
}

This should give an error, right ? as dic["should_give_error"] is not present but it is not giving an error (the Form loads normally). But I can trap it with try..catch(KeyNotFoundException) block...how come ?

[Why the form load can't catch exception?](http://stackoverflow.com/questions/3209706/why-the-form-load-cant-catch-exception) — Tim Schmelter, Dec 02 '13 at 21:07

score 1 · Answer 1 · answered Dec 02 '13 at 20:50

1

I suspect you aren't actually running Form1_Load. Here's a short but complete program to demonstrate the exception being thrown as expected:

using System;
using System.Collections.Generic;
using System.Windows.Forms;

class Test
{
    static void Main()
    {
        Form form = new Form();
        form.Load += Form1_Load;
        Application.Run(form);
    }

    private static void Form1_Load(object sender, EventArgs e)
    {
        Dictionary<string, string> dic = new Dictionary<string, string>();
        dic["666bytes"] = "ME";
        MessageBox.Show(dic["should_give_error"]);
    }
}

Compile and run that, and you get an exception dialog box.

answered Dec 02 '13 at 20:50

Jon Skeet

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Hi, yes I am running the right Form_Load event... I can do all other things during this event like change backcolor, show other Messagebox etc... – Dec 02 '13 at 20:59
@666bytes: Did you try the code I gave? Because as I say, it definitely shows an exception box for me.... – Jon Skeet Dec 02 '13 at 21:20

Kevin T · Answer 2 · 2013-12-02T21:26:17.670

0

You gotta read the documentation better. Quote:

// If a key does not exist, setting the indexer for that key 
// adds a new key/value pair.
openWith["doc"] = "winword.exe";

So, when you call dic["should_give_error"] the program goes, oh, that key doesn't exist, so let's create one. So it does, and returns an empty string.

Edit: Okay, it doesn't return the empty string when you try to get a non-existent key, but the load event can't throw exceptions under certain conditions. But if you leave it like it is, you should have an empty value for the key "should_give_error".

edited Dec 02 '13 at 21:26

answered Dec 02 '13 at 21:13

Kevin T

216
1
6

thats not the case, please check my answer – Dec 02 '13 at 21:31

score 0 · Answer 3 · edited May 23 '17 at 10:25

0

I did found the answer (it's a BUG, not the answer I was expecting) and here are the references ...

edited May 23 '17 at 10:25

Community

1
1

answered Dec 02 '13 at 21:27

Dictionary KeyNotFoundException NOT giving error ... WHY?

3 Answers3