C# Handling Exception in Task with await

Question

I'm new to the async and await keywords in C# and I am using C# 6.0. What is the problem with my code? The DivideByZeroException does not get caught in the catch block. I read that in C# 5 and newer, exceptions can be handled easily with using await keyword surrounded by a try-catch block.

private async void button1_Click(object sender, EventArgs e)
{
    try
    {
        Console.WriteLine("in try");                
        int result = await f(0);
        textBox1.Text = result.ToString();
    }
    catch (Exception)
    {
        Console.WriteLine("in catch");                
    }
    finally
    {
        Console.WriteLine("in finally");                
    }
}

Task<int> f(int x)
{
    return Task<int>.Factory.StartNew(() =>
    {
        return 10 / x;                
    });

}

@CodeCaster while it looks similar, I don't think it's a duplicate. — Evk, Feb 20 '18 at 13:39
I can't reproduce the issue (at least in LinqPad). It prints "in try", "in catch" and "in finally". Have you tried putting a breakpoint in the catch block to see if it really is not entered? — ckuri, Feb 20 '18 at 13:46
@ckuri yes, you are right. I checked again. but the exception just get catched in release mode. in debug mode will not enter catch block! why?! — Hamid Reza Arzaghi, Feb 20 '18 at 13:53

score 0 · Accepted Answer · answered Feb 20 '18 at 14:29

0

It is working in release, but since this is WebForms/WPF or WinForms app, it doesn't have console, so Console.WriteLine never prints anything. Replace:

Console.WriteLine("in catch");

with

textBox1.Text = "in catch";

This will work:

try
{
    textBox1.Text += "in try";               
    int result = await f(0);
    textBox1.Text = result.ToString();
}
catch (Exception)
{
    textBox1.Text += "in catch";                
}
finally
{
    textBox1.Text += "in finally";                
}

answered Feb 20 '18 at 14:29

FCin

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Is there a way to enter the catch block in Debug mode? – Hamid Reza Arzaghi Feb 20 '18 at 14:57
@HamidRezaAZ It will enter catch and after that finally block in both release and debug. Make sure you append text not replace it or just remove textBox1 from finally block – FCin Feb 20 '18 at 15:33

C# Handling Exception in Task with await

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