Windows Store App UI - not responsive - windows-8

Question

I'm trying to get my head around designing a UI that remains responsive while a long running task is being executed.
To that end, I created a simple app in VS2012 and added the following class to it:
using System.Threading.Tasks;
namespace TaskTest
{
class Class1
{
public async Task<int> Async()
{
//simulate a long running process
for (long x = 0; x < long.MaxValue; x++) { }
return 1;
}
}
}
I then modified the main page's LoadState() method thusly:
protected override async void LoadState(Object navigationParameter, Dictionary<String, Object> pageState)
{
await DoLongRunningProcess();
}
private async Task DoLongRunningProcess()
{
var id = 0;
id = await new Class1().Async();
await new MessageDialog(id + "").ShowAsync();
}
I want the page to remain responsive while that process executes. However, when I run this code, the page takes a long time to load. What am I doing wrong?
TIA

Answer 1

async isn't magic; it just gives you the capability to write asynchronous code. In particular, async does not execute code on a background thread. You can use Task.Run to do this.
You may find my async/await intro or the MSDN documentation helpful.

Answer 2

That was helpful. I made the following changes and I got the result I was looking for:
class Class1
{
public int Launch()
{
//throw new Exception("Class1 exception");
for (var i = 0; i < int.MaxValue / 2; i++) ;
return 1;
}
}
...
protected async override void LoadState(Object navigationParameter, Dictionary<String, Object> pageState)
{
var task = DoLongRunningProcess();
await task;
await new MessageDialog(task.Result + "").ShowAsync();
}
private Task<int> DoLongRunningProcess()
{
return Task.Run<int>(() => new Class1().Launch());
}
The page continues to load and after a short pause the message dialog is displayed. Now however, I need to know how to catch exceptions. If I uncomment the //throw new Exception ... line in method Launch(), it is reported as an unhandled exception. I want to catch this exception in the main UI thread (i.e., in the body of method LoadState) but I can't seem to manage it.