Mixing
How to handle exceptions with ContinueWith and WhenAll?
-1
I am trying to load multiple files asynchronously and inform UI when ever each file is done loading,
_loadCancellationTokenSource = new CancellationTokenSource();
TaskScheduler scheduler = TaskScheduler.FromCurrentSynchronizationContext();
var files = await picker.PickMultipleFilesAsync();
LoadedFiles.Clear();
loads = await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsCompleted) LoadedFiles.Add(file.Path);
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, scheduler);
return load;
}));
private Task<Foo> LoadAsync(StorageFile file)
{
// exception may be thrown inside load
return Load(file, _loadCancellationTokenSource.Token);
}
The problem Is when exception is thrown, it is not handled. I know why, because ContinueWith creates a new task but im returning the old task.
This is because ContinueWith is a void task. but I dont know how to return the result correctly. Im not sure if its safe to use t.Result because it may block the UI thread?
PS, I've tried this code but I get a task was cancelled exception and app crashes even though I'm not cancelling any tasks. only a few exceptions are thrown for loading some files.
load = (await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.NotOnRanToCompletion, scheduler);
return load.ContinueWith(t =>
{
LoadedFiles.Add(file.Path);
return (file, t.Result);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.OnlyOnRanToCompletion, scheduler); ;
})));
c# asynchronous exception-handling task result
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
add a comment |
-1
I am trying to load multiple files asynchronously and inform UI when ever each file is done loading,
_loadCancellationTokenSource = new CancellationTokenSource();
TaskScheduler scheduler = TaskScheduler.FromCurrentSynchronizationContext();
var files = await picker.PickMultipleFilesAsync();
LoadedFiles.Clear();
loads = await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsCompleted) LoadedFiles.Add(file.Path);
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, scheduler);
return load;
}));
private Task<Foo> LoadAsync(StorageFile file)
{
// exception may be thrown inside load
return Load(file, _loadCancellationTokenSource.Token);
}
The problem Is when exception is thrown, it is not handled. I know why, because ContinueWith creates a new task but im returning the old task.
This is because ContinueWith is a void task. but I dont know how to return the result correctly. Im not sure if its safe to use t.Result because it may block the UI thread?
PS, I've tried this code but I get a task was cancelled exception and app crashes even though I'm not cancelling any tasks. only a few exceptions are thrown for loading some files.
load = (await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.NotOnRanToCompletion, scheduler);
return load.ContinueWith(t =>
{
LoadedFiles.Add(file.Path);
return (file, t.Result);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.OnlyOnRanToCompletion, scheduler); ;
})));
c# asynchronous exception-handling task result
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
1
IsCompletedwill betrueeven ifIsFaultedorIsCancelledaretrue. WhileTaskStatus.RanToCompletionwill be true only whenIsFaultedandIsCancelledare false. You could add some conditions toContinueWithhandling different TaskContinuationOptions.
– Jimi
Jan 1 at 6:01
add a comment |
-1
-1
-1
I am trying to load multiple files asynchronously and inform UI when ever each file is done loading,
_loadCancellationTokenSource = new CancellationTokenSource();
TaskScheduler scheduler = TaskScheduler.FromCurrentSynchronizationContext();
var files = await picker.PickMultipleFilesAsync();
LoadedFiles.Clear();
loads = await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsCompleted) LoadedFiles.Add(file.Path);
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, scheduler);
return load;
}));
private Task<Foo> LoadAsync(StorageFile file)
{
// exception may be thrown inside load
return Load(file, _loadCancellationTokenSource.Token);
}
The problem Is when exception is thrown, it is not handled. I know why, because ContinueWith creates a new task but im returning the old task.
This is because ContinueWith is a void task. but I dont know how to return the result correctly. Im not sure if its safe to use t.Result because it may block the UI thread?
PS, I've tried this code but I get a task was cancelled exception and app crashes even though I'm not cancelling any tasks. only a few exceptions are thrown for loading some files.
load = (await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.NotOnRanToCompletion, scheduler);
return load.ContinueWith(t =>
{
LoadedFiles.Add(file.Path);
return (file, t.Result);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.OnlyOnRanToCompletion, scheduler); ;
})));
c# asynchronous exception-handling task result
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
I am trying to load multiple files asynchronously and inform UI when ever each file is done loading,
_loadCancellationTokenSource = new CancellationTokenSource();
TaskScheduler scheduler = TaskScheduler.FromCurrentSynchronizationContext();
var files = await picker.PickMultipleFilesAsync();
LoadedFiles.Clear();
loads = await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsCompleted) LoadedFiles.Add(file.Path);
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, scheduler);
return load;
}));
private Task<Foo> LoadAsync(StorageFile file)
{
// exception may be thrown inside load
return Load(file, _loadCancellationTokenSource.Token);
}
The problem Is when exception is thrown, it is not handled. I know why, because ContinueWith creates a new task but im returning the old task.
This is because ContinueWith is a void task. but I dont know how to return the result correctly. Im not sure if its safe to use t.Result because it may block the UI thread?
PS, I've tried this code but I get a task was cancelled exception and app crashes even though I'm not cancelling any tasks. only a few exceptions are thrown for loading some files.
load = (await Task.WhenAll(files.Select(file =>
{
var load = LoadAsync(file);
load.ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.NotOnRanToCompletion, scheduler);
return load.ContinueWith(t =>
{
LoadedFiles.Add(file.Path);
return (file, t.Result);
}, _loadCancellationTokenSource.Token, TaskContinuationOptions.OnlyOnRanToCompletion, scheduler); ;
})));
c# asynchronous exception-handling task result
c# asynchronous exception-handling task result
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
edited Jan 1 at 6:27
M.kazem Akhgary
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
asked Jan 1 at 5:39
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
12.1k53473
1
IsCompletedwill betrueeven ifIsFaultedorIsCancelledaretrue. WhileTaskStatus.RanToCompletionwill be true only whenIsFaultedandIsCancelledare false. You could add some conditions toContinueWithhandling different TaskContinuationOptions.
– Jimi
Jan 1 at 6:01
add a comment |
1
IsCompletedwill betrueeven ifIsFaultedorIsCancelledaretrue. WhileTaskStatus.RanToCompletionwill be true only whenIsFaultedandIsCancelledare false. You could add some conditions toContinueWithhandling different TaskContinuationOptions.
– Jimi
Jan 1 at 6:01
1
1
IsCompleted will be true even if IsFaulted or IsCancelled are true. While TaskStatus.RanToCompletion will be true only when IsFaulted and IsCancelled are false. You could add some conditions to ContinueWith handling different TaskContinuationOptions.– Jimi
Jan 1 at 6:01
IsCompleted will be true even if IsFaulted or IsCancelled are true. While TaskStatus.RanToCompletion will be true only when IsFaulted and IsCancelled are false. You could add some conditions to ContinueWith handling different TaskContinuationOptions.– Jimi
Jan 1 at 6:01
add a comment |
1 Answer
1
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oldest
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Thanks to @Jimi I was able to solve this problem by looking at Task status.
loads = (await Task.WhenAll(files.Select(file =>
{
return LoadAsync(file).ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
if (t.Status == TaskStatus.RanToCompletion)
{
LoadedFiles.Add(file.Path);
return t.Result;
}
return null;
}, scheduler);
}))).Where(x => x != null).ToArray();
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
add a comment |
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Thanks to @Jimi I was able to solve this problem by looking at Task status.
loads = (await Task.WhenAll(files.Select(file =>
{
return LoadAsync(file).ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
if (t.Status == TaskStatus.RanToCompletion)
{
LoadedFiles.Add(file.Path);
return t.Result;
}
return null;
}, scheduler);
}))).Where(x => x != null).ToArray();
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
add a comment |
0
Thanks to @Jimi I was able to solve this problem by looking at Task status.
loads = (await Task.WhenAll(files.Select(file =>
{
return LoadAsync(file).ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
if (t.Status == TaskStatus.RanToCompletion)
{
LoadedFiles.Add(file.Path);
return t.Result;
}
return null;
}, scheduler);
}))).Where(x => x != null).ToArray();
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
add a comment |
0
0
0
Thanks to @Jimi I was able to solve this problem by looking at Task status.
loads = (await Task.WhenAll(files.Select(file =>
{
return LoadAsync(file).ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
if (t.Status == TaskStatus.RanToCompletion)
{
LoadedFiles.Add(file.Path);
return t.Result;
}
return null;
}, scheduler);
}))).Where(x => x != null).ToArray();
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
Thanks to @Jimi I was able to solve this problem by looking at Task status.
loads = (await Task.WhenAll(files.Select(file =>
{
return LoadAsync(file).ContinueWith(t =>
{
if (t.IsFaulted) NotifyUser(t.Exception.Message, NotifyType.ErrorMessage);
if (t.IsCanceled) NotifyUser("operation was canceled.", NotifyType.ErrorMessage);
if (t.Status == TaskStatus.RanToCompletion)
{
LoadedFiles.Add(file.Path);
return t.Result;
}
return null;
}, scheduler);
}))).Where(x => x != null).ToArray();
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
answered Jan 1 at 6:50
M.kazem AkhgaryM.kazem Akhgary
12.1k53473
12.1k53473
add a comment |
add a comment |
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1
IsCompletedwill betrueeven ifIsFaultedorIsCancelledaretrue. WhileTaskStatus.RanToCompletionwill be true only whenIsFaultedandIsCancelledare false. You could add some conditions toContinueWithhandling different TaskContinuationOptions.– Jimi
Jan 1 at 6:01