ABP框架系列之二十八：(Handling-Exceptions-异常处理)

Introduction

This document is for ASP.NET MVC and Web API. If you're interested in ASP.NET Core, see ASP.NET Core documentation.

In a web application, exceptions are usually handled in MVC Controller actions and Web API Controller actions. When an exception occurs, application user somehow informed about the error and optionally reason of the error.

在Web应用程序中，异常通常是在MVC控制器操作和Web API控制器操作中处理的。当异常发生时，应用程序用户被告知错误和错误的可选原因。

If an error occured in a regular HTTP request, an error page is shown. If an error occured in an AJAX request, server sends error information to the client and then client handles and shows the error to the user.

如果在常规HTTP请求中出现错误，则显示错误页面。如果Ajax请求中出现错误，服务器向客户端发送错误信息，然后客户端处理并向用户显示错误。

Handling exceptions in all web request is a tedious and repeating work. ASP.NET Boilerplate automates this. You almost never need to explicitly handle any exception. ASP.NET Boilerplate handles all exceptions, logs them and returns appropriate and formatted response to the client. Also, handles these response in the client and show error messages to the user.

处理所有Web请求中的异常是一项单调乏味的重复工作。ASP.NET样板自动化这个。您几乎从不需要显式地处理任何异常。ASP.NET样板处理所有的异常，日志，返回适当格式的响应到客户端。此外，在客户机中处理这些响应并向用户显示错误消息。

Enabling Error Handling

To enable error handling for ASP.NET MVC Controllers, customErrors mode must be enabled for ASP.NET MVC applications.

<customErrors mode="On" />

It also can be 'RemoteOnly' if you do not want to handler errors in local computer. Note that this is only required for ASP.NET MVC Controllers, not needed for Web API Controllers.

If you have already handling exceptions in a global filter then it may hide exceptions and ABP's exception handling may not work as you expected. So, if you do that, do it carefully.

它也可以“remoteonly”如果你不想在本地计算机处理程序错误。请注意，这仅仅是ASP.NET所需的MVC控制器，Web API控制器不需要。

如果您已经在全局筛选器中处理异常，则它可能隐藏异常，而ABP的异常处理可能不象您预期的那样工作。所以，如果你这样做，要小心。

Non-Ajax Requests

If request is not AJAX, an error page is shown.

Showing Exceptions

Here, there is an MVC controller action which throws an arbitrary exception:

这里有一个MVC控制器动作，它抛出一个任意异常：

public ActionResult Index()
{
    throw new Exception("A sample exception message...");
}

Surely, this exception could be thrown by another method that is called from this action. ASP.NET Boilerplate handles this exception, logs it and shows 'Error.cshtml' view. You can customize this view to show the error. An example Error view (default Error view in ASP.NET Boilerplate templates):

ASP.NET Boilerplate hides details of the exception from users and shows a standard (and localizable) error message, unless you explicitly throw a UserFriendlyException.

UserFriendlyException

UserFriendlyException is a special type of exception that is directly shown to the user. See the sample below:

public ActionResult Index()
{
    throw new UserFriendlyException("Ooppps! There is a problem!", "You are trying to see a product that is deleted...");
}

ASP.NET Boilerplate logs it but does not hide exception in this time:

So, if you want to show a special error message to users, just throw a UserFriendlyException (or an exception derived from it).

Error Model

ASP.NET Boilerplate passes an ErrorViewModel object as model to the Error view:

public class ErrorViewModel
{
    public AbpErrorInfo ErrorInfo { get; set; }

    public Exception Exception { get; set; }
}

ErrorInfo contains detailed informations about the error that can be shown to the user. Exception object is the thrown exception. You can check it and show additional informations if you want. For example, we can show validation errors if it's an AbpValidationException:

AJAX Requests

If return type of MVC action is JsonResult (or Task<JsonResult for async actions), ASP.NET Boilerplate returns a JSON object to the client on exceptions. Sample return object for an error:

{
  "targetUrl": null,
  "result": null,
  "success": false,
  "error": {
    "message": "An internal error occured during your request!",
    "details": "..."
  },
  "unAuthorizedRequest": false
}

success: false indicates that there is an error. error object provides error message and details.

When you use ASP.NET Boilerplate's infrastructure to make AJAX request in client side, it automatically handles this JSON object and shows error message to the user using message API. See AJAX API for more information.

Exception Event

When ASP.NET Boilerplare handles any exception, it triggers AbpHandledExceptionData event that can be registered to be informed (See eventbus documentation for more information about Event Bus). Example:

public class MyExceptionHandler : IEventHandler<AbpHandledExceptionData>, ITransientDependency
{
    public void HandleEvent(AbpHandledExceptionData eventData)
    {
        //TODO: Check eventData.Exception!
    }
}

If you put this example class into your application (generally into your Web project), HandleEvent method will be called for all exceptions handled by ASP.NET Boilerplate. So, you can investigate the Exception object in detail.