正确使用应用程序配置文件中的设置
我最近创建了一个 Windows 服务。它忠实地做的一件事是将所有错误记录到应用程序日志中。我有以下代码可以执行此操作：
Dim appLog = New System.Diagnostics.EventLog With {.Source = "MyService"}
appLog.WriteEntry(message, EventLogEntryType.Error, transactionID)
我的 app.config 中也有以下内容：
<system.diagnostics>
<sources>
<source name="MyService" switchName="DefaultSwitch">
<listeners>
<!--<add name="FileLog"/>-->
<add name="EventLog"/>
</listeners>
</source>
</sources>
<switches>
<add name="DefaultSwitch" value="Information" />
</switches>
<sharedListeners>
<!--<add name="FileLog"
type="Microsoft.VisualBasic.Logging.FileLogTraceListener, Microsoft.VisualBasic, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"
initializeData="FileLogWriter"/>-->
<add name="EventLog" type="System.Diagnostics.EventLogTraceListener" initializeData="MyService"/>
</sharedListeners>
</system.diagnostics>
即使不以编程方式设置 EventLog 的 Source 属性，我也希望上面的代码也能正常工作，因为我已经在配置文件中定义了源。但是，如果我删除 With {.Source = "MyService"}，则会收到异常，这表明应在调用 WriteEntry 方法之前设置 Source 属性。那么，配置 XML 中的内容的用途是什么？
I recently created a Windows service. One thing that it faithfully does is log any errors to the Application log. I have the following code that does this:
Dim appLog = New System.Diagnostics.EventLog With {.Source = "MyService"}
appLog.WriteEntry(message, EventLogEntryType.Error, transactionID)
I also have the following in my app.config:
<system.diagnostics>
<sources>
<source name="MyService" switchName="DefaultSwitch">
<listeners>
<!--<add name="FileLog"/>-->
<add name="EventLog"/>
</listeners>
</source>
</sources>
<switches>
<add name="DefaultSwitch" value="Information" />
</switches>
<sharedListeners>
<!--<add name="FileLog"
type="Microsoft.VisualBasic.Logging.FileLogTraceListener, Microsoft.VisualBasic, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"
initializeData="FileLogWriter"/>-->
<add name="EventLog" type="System.Diagnostics.EventLogTraceListener" initializeData="MyService"/>
</sharedListeners>
</system.diagnostics>
I would expect that my code above should work even without setting the Source property of EventLog programmatically because I've already defined the source in the config file. But if I remove With {.Source = "MyService"}, then I get an Exception, which that says that the Source property should be set before calling WriteEntry method. So, what's purpose of the stuff in the configuration XML?
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幸运的是，我在开发另一个应用程序时偶然发现了一个答案，或者至少是部分答案。使用 My.Application.Log 对象时，配置文件中的设置很重要。例如：
My.Application.Log.WriteEntry(errMsg)将根据 app.config 中的设置写入文件或事件查看器。因此，在这种情况下，不会直接从代码调用
EventLog类。这为我提供了额外的灵活性，可以将日志格式从事件查看器“热交换”到文件，例如，无需更改任何代码或重新编译。但我确实注意到的一件事是As luck has it, I've stumbled on an answer, or at least a partial one while working on a different app. The settings in the config file matter when using
My.Application.Logobject. For example:My.Application.Log.WriteEntry(errMsg)will write to a file or to the Event Viewer depending on the setting in app.config.So, in this case, the
EventLogclass is not called directly from code. This gives me the extra flexibility to "hot-swap" the log format from Event Viewer to file, for example, without changing any code or recompiling. One thing that I did notice though is that the Name property of the<source>element needs to be set to "DefaultSource". Otherwise, events don't get logged. There's probably a way to change that, but I didn't see a need, so I didn't investigate further. Hopefully, this will be useful to somebody.