Unity: The type LogWriter cannot be constructed

问题

For the following "project" I am getting a very annoying and inexplicable error when resolving Unity for DI.

InvalidOperationException - The type LogWriter cannot be constructed. You must configure the container to supply this value.

?ex.Message; "Resolution of the dependency failed, type = \"WindowsFormsApplication1.Performance\", name = \"(none)\".\r\nException occurred while: while resolving.\r\nException is: InvalidOperationException - The type LogWriter cannot be constructed. You must configure the container to supply this value.\r\n-----------------------------------------------\r\nAt the time of the exception, the container was:\r\n\r\n Resolving WindowsFormsApplication1.Performance,(none)\r\n Resolving parameter \"lw\" of constructor WindowsFormsApplication1.Performance(Microsoft.Practices.EnterpriseLibrary.Logging.LogWriter lw, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionManager em)\r\n Resolving Microsoft.Practices.EnterpriseLibrary.Logging.LogWriter,(none)\r\n"

?ex.StackTrace; " at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable1 resolverOverrides) in e:\\Builds\\Unity\\UnityTemp\\Compile\\Unity\\Unity\\Src\\UnityContainer.cs:line 515\r\n at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, String name, IEnumerable1 resolverOverrides) in e:\Builds\Unity\UnityTemp\Compile\Unity\Unity\Src\UnityContainer.cs:line 485\r\n at Microsoft.Practices.Unity.UnityContainer.Resolve(Type t, String name, ResolverOverride[] resolverOverrides) in e:\Builds\Unity\UnityTemp\Compile\Unity\Unity\Src\UnityContainer.cs:line 173\r\n at Microsoft.Practices.Unity.UnityContainerExtensions.Resolve[T](IUnityContainer container, ResolverOverride[] overrides) in e:\Builds\Unity\UnityTemp\Compile\Unity\Unity\Src\UnityContainerExtensions.cs:line 504\r\n at WindowsFormsApplication1.Form1.OnLoad(EventArgs e) in D:\Devzone\Tasking\WindowsFormsApplication1\Form1.cs:line 33"

In a form:

  protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);

            try
            {
                IUnityContainer container = new UnityContainer();
                Performance p = container.Resolve<Performance>();
            }
            catch (Exception ex)
            {

            }
        }

Dependency class:

 public class Performance
    {
        public Performance(LogWriter lw, ExceptionManager em)
        {
        }
    }

Configuration File:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <section name="loggingConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.LoggingSettings, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="true" />
        <section name="exceptionHandling" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Configuration.ExceptionHandlingSettings, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="true" />
    </configSections>
    <loggingConfiguration name="" tracingEnabled="true" defaultCategory="General">
        <listeners>
            <add name="Event Log Listener" type="Microsoft.Practices.EnterpriseLibrary.Logging.TraceListeners.FormattedEventLogTraceListener, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
                listenerDataType="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.FormattedEventLogTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
                source="Enterprise Library Logging" formatter="Text Formatter"
                log="" machineName="." traceOutputOptions="None" />
        </listeners>
        <formatters>
            <add type="Microsoft.Practices.EnterpriseLibrary.Logging.Formatters.TextFormatter, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
                template="Timestamp: {timestamp}{newline}&#xA;Message: {message}{newline}&#xA;Category: {category}{newline}&#xA;Priority: {priority}{newline}&#xA;EventId: {eventid}{newline}&#xA;Severity: {severity}{newline}&#xA;Title:{title}{newline}&#xA;Machine: {localMachine}{newline}&#xA;App Domain: {localAppDomain}{newline}&#xA;ProcessId: {localProcessId}{newline}&#xA;Process Name: {localProcessName}{newline}&#xA;Thread Name: {threadName}{newline}&#xA;Win32 ThreadId:{win32ThreadId}{newline}&#xA;Extended Properties: {dictionary({key} - {value}{newline})}"
                name="Text Formatter" />
        </formatters>
        <categorySources>
            <add switchValue="All" name="General">
                <listeners>
                    <add name="Event Log Listener" />
                </listeners>
            </add>
            <add switchValue="All" name="Category2" />
        </categorySources>
        <specialSources>
            <allEvents switchValue="All" name="All Events" />
            <notProcessed switchValue="All" name="Unprocessed Category" />
            <errors switchValue="All" name="Logging Errors &amp; Warnings">
                <listeners>
                    <add name="Event Log Listener" />
                </listeners>
            </errors>
        </specialSources>
    </loggingConfiguration>
    <exceptionHandling>
        <exceptionPolicies>
            <add name="Policy">
                <exceptionTypes>
                    <add name="All Exceptions" type="System.Exception, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
                        postHandlingAction="NotifyRethrow" />
                </exceptionTypes>
            </add>
        </exceptionPolicies>
    </exceptionHandling>
</configuration>

回答1:

You need to add the Enterprise Library extension to your container. Without it, the container doesn't read the config file and therefore doesn't know how to create Entlib objects, like the LogWriter.

回答2:

Activation error occured while trying to get instance of type LogWriter, key ""

check your config file it must have correct default 'loggingConfiguration' section

回答3:

In order for Unity to construct your Performance class, it needs to know how to construct the implementation of ILogWriter.

I cannot see anywhere in your code where you tell Unity what class to create for the ILogWriter interface, so I suspect you may need to add this.

回答4:

Try this:

protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);

            try
            {
                IUnityContainer container = new UnityContainer();
                container.RegisterType<ILogWriter, LogWriter>();
                container.RegisterType<ExceptionManager>();
                container.RegisterType<Performance>(new InjectionConstructor(typeof(ILogWriter), typeof(ExceptionManager));                    
                Performance p = container.Resolve<Performance>();
            }
            catch (Exception ex)
            {

            }
        }

回答5:

LogWriter does not have an empty constructor or a constructor with all concrete types parameters: LogWriter Constructor.

So Unity fails in building it and as it says, it will need your help by configuring the container to provide an implementation.

As a confirmation, ExceptionManager will probably be resolved ok, since it has only one constructor, parameterless as well :)

来源：https://stackoverflow.com/questions/12950547/unity-the-type-logwriter-cannot-be-constructed

标签

unity-container