{"id":821,"date":"2023-03-09T13:43:34","date_gmt":"2023-03-09T06:43:34","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=821"},"modified":"2023-03-21T07:20:54","modified_gmt":"2023-03-21T00:20:54","slug":"csharp-task-handle-exception","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-concurrency\/csharp-task-handle-exception\/","title":{"rendered":"Handling Exceptions in C# Task"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to handle exceptions raised by the asynchronous operation executed by the Task<\/code> objects.<\/p>\n\n\n\n

Introduction to AggregateException<\/h2>\n\n\n\n

In general, when a Task<\/a><\/code> encounters an exception, it will propagate the exception to the calling thread. If a Task<\/code> contains nested tasks, any asynchronous operations performed within these tasks may also result in multiple exceptions being thrown.<\/p>\n\n\n\n

To propagate all the exceptions to the calling thread, the Task<\/code> wraps them in an AggregateException<\/code><\/code> object. <\/p>\n\n\n\n

The AggregateException<\/code><\/code> object has the InnerExceptions<\/code> property that contains all the original exceptions. The InnerExceptions<\/code> is a read-only collection of the Exception<\/code> instances.<\/p>\n\n\n\n

To handle these exceptions, you can enumerate them through the InnerExceptions<\/code> property of the AggregateException<\/code> object using a foreach<\/code> loop.<\/p>\n\n\n\n

Alternatively, you can handle the original exceptions using the AggregateException.Handle<\/code> method:<\/p>\n\n\n

public<\/span> void Handle (Func<Exception<\/span>,bool> predicate);<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
It’s important to note that the Task<\/code> will wrap any exceptions that occur within an AggregationException<\/code> object, even if a single exception is raised.<\/p>\n\n\n\n
Handling AggregateException example<\/h2>\n\n\n\n
The following program illustrates how to handle exceptions in an asynchronous operation executed by a task.<\/p>\n\n\n
decimal<\/span> Divide<\/span>(decimal<\/span> a, decimal<\/span> b<\/span>)<\/span>\n{\n    Thread.Sleep(1000<\/span>);\n\n    return<\/span> a \/ b;\n}\n\ntry<\/span>\n{\n    var<\/span> task = Task.Run(() => Divide(10<\/span>, 0<\/span>));\n    var<\/span> result = task.Result;\n}\ncatch<\/span> (AggregateException ae)\n{\n    ae.Flatten().Handle(e =>\n    {\n        if<\/span> (e is<\/span> DivideByZeroException)\n        {\n            Console.WriteLine(e.Message);\n            return<\/span> true<\/span>;\n        }\n        else<\/span>\n        {\n            throw<\/span> e;\n        }\n    });\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
How it works.<\/p>\n\n\n\n
First, define a method Divide()<\/code> that takes two decimal numbers and returns the result of dividing them after a delay of one second:<\/p>\n\n\n
decimal<\/span> Divide<\/span>(decimal<\/span> a, decimal<\/span> b<\/span>)<\/span>\n{\n    Thread.Sleep(1000<\/span>);\n\n    return<\/span> a \/ b;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, use the Task.Run<\/code>()<\/code> method to run the Divide()<\/code> method asynchronously in a separate thread. Since we use the arguments 10 and 0, the Divide()<\/code> method will throw a DivideByZeroException<\/code> exception:<\/p>\n\n\n
var<\/span> task = Task.Run(() => Divide(10<\/span>, 0<\/span>));<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In the exception handler, we use the Handle()<\/code> method of the AggregateException<\/code> class to handle each inner exception.<\/p>\n\n\n\n
If the exception is DivideByZeroException<\/code>, the program outputs the error message to the console. Otherwise, it rethrows the same exception.<\/p>\n\n\n\n
When you run the program, you’ll see the following output:<\/p>\n\n\n
Attempted to divide by<\/span> zero.<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
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  • Use the try...catch<\/code> to catch the AggregateException<\/code> thrown by the asynchronous operation executed by a Task<\/code>.<\/li>\n\n\n\n
  • Use the AggregateException.Handle()<\/code> method to handle exceptions.<\/li>\n<\/ul>\n
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Third, use the try…catch<\/a> block to catch any exceptions thrown by the method. Since the asynchronous operation throws an AggregateException<\/code>, we catch and handle it in the catch<\/code> block.<\/p>\n\n\n\n