发生了预料之外的错误:
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentException: Specified Visual is already a child of another Visual or the root of a CompositionTarget.
at System.Windows.Media.VisualCollection.Insert(Int32 index, Visual visual)
at System.Windows.Controls.UIElementCollection.InsertInternal(Int32 index, UIElement element)
at JiJiDownForWPF.UserControls.u_Download.PRdoeLVoED1QKHgKC1.iW5Woea2YsiNjlZDLDO(Object , Int32 , Object )
at JiJiDownForWPF.UserControls.u_Download.PRdoeLVoED1QKHgKC1.TlUq7pV0wq()
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
at System.Delegate.DynamicInvokeImpl(Object[] args)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)