Disposing WPF User Controls

Question

I have created a custom WPF user control which is intended to be used by a third party  My control has a private member which is disposable  and I would like to ensure that its dispose method will always get called once the containing window application is closed  However  UserControl is not disposable  I tried implementing the IDisposable interface and subscribing to the Unloaded event but neither get called when the host application closes  MSDN says that the Unloaded event may not be raised at all  And it might also be triggered more than once  that is when user changes theme  If at all possible  I don t want to rely on consumers of my control remembering to call a specific Dispose method   public partial class MyWpfControl   UserControl         SomeDisposableObject x           where does this code go       void Somewhere                    if  x    null                          x Dispose                 x   null                         The only solution I have found so far is to subscribe to the Dispatcher s ShutdownStarted event  Is this a reasonable approach  this Dispatcher ShutdownStarted    Dispatcher ShutdownStarted

User · Accepted Answer

Interesting blog post here   http   geekswithblogs net cskardon archive 2008 06 23 dispose-of-a-wpf-usercontrol-ish aspx   It mentions subscribing to Dispatcher ShutdownStarted to dispose of your resources

User · Answer

An UserControl has a Destructor  why don t you use that    MyWpfControl                    Dispose of any Disposable items here

User · Answer

An UserControl has a Destructor  why don t you use that    MyWpfControl                    Dispose of any Disposable items here

User · Answer

My scenario is little different  but the intent is same i would like to know when the parent window hosting my user control is closing closed as The view i e my usercontrol  should invoke the presenters oncloseView to execute some functionality and perform clean up    well we are implementing a MVP pattern on a WPF PRISM application     I just figured that in the Loaded event of the usercontrol  i can hook up my ParentWindowClosing method to the Parent windows Closing event  This way my Usercontrol can be aware when the Parent window is being closed and act accordingly

User · Answer

Dispatcher ShutdownStarted event is fired only at the end of application  It s worth to call the disposing logic just when control gets out of use  In particular it frees resources when control is used many times during application runtime  So ioWint s solution is preferable  Here s the code   public MyWpfControl          InitializeComponent         Loaded     s  e    gt       only at this point the control is ready          Window GetWindow this     get the parent window                 Closing     s1  e1    gt  Somewhere      disposing logic here

User · Answer

An UserControl has a Destructor  why don t you use that    MyWpfControl                    Dispose of any Disposable items here

User · Answer

You have to be careful using the destructor  This will get called on the GC Finalizer thread  In some cases the resources that your freeing may not like being released on a different thread from the one they were created on

User · Answer

My scenario is little different  but the intent is same i would like to know when the parent window hosting my user control is closing closed as The view i e my usercontrol  should invoke the presenters oncloseView to execute some functionality and perform clean up    well we are implementing a MVP pattern on a WPF PRISM application     I just figured that in the Loaded event of the usercontrol  i can hook up my ParentWindowClosing method to the Parent windows Closing event  This way my Usercontrol can be aware when the Parent window is being closed and act accordingly

User · Answer

I m thinking unload is called all but at hard exist in 4 7   But  if you are playing around with older versions of  Net  try doing this in your loading method   e Handled   true    I don t think older versions will unload until loading is handled   Just posting because I see others still asking this question  and haven t seen this proposed as a solution   I only touch  Net a few times a year  and ran into this a few years back   But  I wonder if it s as simple as unload not being called until loading has finished   Seems like it works for me  but again in newer  Net it seems to always call unload even if loading isn t marked as handled

User · Answer

I m thinking unload is called all but at hard exist in 4 7   But  if you are playing around with older versions of  Net  try doing this in your loading method   e Handled   true    I don t think older versions will unload until loading is handled   Just posting because I see others still asking this question  and haven t seen this proposed as a solution   I only touch  Net a few times a year  and ran into this a few years back   But  I wonder if it s as simple as unload not being called until loading has finished   Seems like it works for me  but again in newer  Net it seems to always call unload even if loading isn t marked as handled

User · Answer

I use the following Interactivity Behavior to provide an unloading event to WPF UserControls  You can include the behavior in the UserControls XAML  So you can have the functionality without placing the logic it in every single UserControl   XAML declaration   xmlns i  http   schemas microsoft com expression 2010 interactivity    lt i Interaction Behaviors gt       lt behaviors UserControlSupportsUnloadingEventBehavior UserControlClosing  UserControlClosingHandler    gt   lt  i Interaction Behaviors gt    CodeBehind handler   private void UserControlClosingHandler object sender  EventArgs e           to unloading stuff here     Behavior Code        lt summary gt      This behavior raises an event when the containing window of a  lt see cref  UserControl   gt  is closing       lt  summary gt  public class UserControlSupportsUnloadingEventBehavior   System Windows Interactivity Behavior lt UserControl gt        protected override void OnAttached                 AssociatedObject Loaded    UserControlLoadedHandler             protected override void OnDetaching                 AssociatedObject Loaded -  UserControlLoadedHandler          var window   Window GetWindow AssociatedObject           if  window    null              window Closing -  WindowClosingHandler                  lt summary gt          Registers to the containing windows Closing event when the UserControl is loaded           lt  summary gt      private void UserControlLoadedHandler object sender  RoutedEventArgs e                var window   Window GetWindow AssociatedObject           if  window    null              throw new Exception                   The UserControl  0  is not contained within a Window  The UserControlSupportsUnloadingEventBehavior cannot be used                        FormatWith AssociatedObject GetType   Name             window Closing    WindowClosingHandler                  lt summary gt          The containing window is closing  raise the UserControlClosing event           lt  summary gt      private void WindowClosingHandler object sender  CancelEventArgs e                OnUserControlClosing                    lt summary gt          This event will be raised when the containing window of the associated  lt see cref  UserControl   gt  is closing           lt  summary gt      public event EventHandler UserControlClosing       protected virtual void OnUserControlClosing                 var handler   UserControlClosing          if  handler    null               handler this  EventArgs Empty

User · Answer

Dispatcher ShutdownStarted event is fired only at the end of application  It s worth to call the disposing logic just when control gets out of use  In particular it frees resources when control is used many times during application runtime  So ioWint s solution is preferable  Here s the code   public MyWpfControl          InitializeComponent         Loaded     s  e    gt       only at this point the control is ready          Window GetWindow this     get the parent window                 Closing     s1  e1    gt  Somewhere      disposing logic here

User · Answer

You have to be careful using the destructor  This will get called on the GC Finalizer thread  In some cases the resources that your freeing may not like being released on a different thread from the one they were created on

User · Answer

An UserControl has a Destructor  why don t you use that    MyWpfControl                    Dispose of any Disposable items here

User · Answer

I use the following Interactivity Behavior to provide an unloading event to WPF UserControls  You can include the behavior in the UserControls XAML  So you can have the functionality without placing the logic it in every single UserControl   XAML declaration   xmlns i  http   schemas microsoft com expression 2010 interactivity    lt i Interaction Behaviors gt       lt behaviors UserControlSupportsUnloadingEventBehavior UserControlClosing  UserControlClosingHandler    gt   lt  i Interaction Behaviors gt    CodeBehind handler   private void UserControlClosingHandler object sender  EventArgs e           to unloading stuff here     Behavior Code        lt summary gt      This behavior raises an event when the containing window of a  lt see cref  UserControl   gt  is closing       lt  summary gt  public class UserControlSupportsUnloadingEventBehavior   System Windows Interactivity Behavior lt UserControl gt        protected override void OnAttached                 AssociatedObject Loaded    UserControlLoadedHandler             protected override void OnDetaching                 AssociatedObject Loaded -  UserControlLoadedHandler          var window   Window GetWindow AssociatedObject           if  window    null              window Closing -  WindowClosingHandler                  lt summary gt          Registers to the containing windows Closing event when the UserControl is loaded           lt  summary gt      private void UserControlLoadedHandler object sender  RoutedEventArgs e                var window   Window GetWindow AssociatedObject           if  window    null              throw new Exception                   The UserControl  0  is not contained within a Window  The UserControlSupportsUnloadingEventBehavior cannot be used                        FormatWith AssociatedObject GetType   Name             window Closing    WindowClosingHandler                  lt summary gt          The containing window is closing  raise the UserControlClosing event           lt  summary gt      private void WindowClosingHandler object sender  CancelEventArgs e                OnUserControlClosing                    lt summary gt          This event will be raised when the containing window of the associated  lt see cref  UserControl   gt  is closing           lt  summary gt      public event EventHandler UserControlClosing       protected virtual void OnUserControlClosing                 var handler   UserControlClosing          if  handler    null               handler this  EventArgs Empty

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