// This method should only be called from Dispose. Otherwise assumptions about the disposing/finalize state could be violated.
// force - when true, remove this subclass from the WndProc chain regardless of
// its current position. When false, remove this subclass only
// if it is possible to do so without damaging other WndProcs
// (i.e. only if this is at the head of the chain).
//
// Removing this subclass from the WndProc chain when it is not at the head
// also removes all other WndProcs that appear before this one on the chain,
// so is generally not appropriate. It is OK in the following situations:
// a) in response to the WM_NCDESTROY message
// b) in response to the AppDomainProcessExit event
// c) in response to the AppDomainExit event
// In cases (a) and (b) the HWND is being destroyed, so the earlier
// WndProcs are no longer useful anyway. In case (c), we have to remove
// all managed code from the chain lest it be called after it has been
// removed from memory; removing earlier WndProcs is unfortunate, but
// necessary. [Note that at AppDomainExit we remove all managed WndProcs,
// regardless of which AppDomain they came from. There is room for
// improvement here - we could remove only the ones belong to the AppDomain
// that is exiting. This situation seems too unlikely to worry about in V1.]
//
// This method returns true if the subclass is no longer in the WndProc chain.
//
private bool UnhookWindowProc(bool force)
{
// if we're not in the WndProc chain, there's nothing to do
if (_bond == Bond.Unattached || _bond == Bond.Detached)
{
return(true);
}
// we'll remove ourselves from the chain if we're at the head, or if
// the 'force' parameter was true.
if (!force)
{
NativeMethods.WndProc currentWndProc = UnsafeNativeMethods.GetWindowLongWndProc(new HandleRef(this, _hwndAttached));
force = (currentWndProc == _attachedWndProc);
}
// if we're not unhooking, return and report
if (!force)
{
return(false);
}
// unhook from the tracker
_bond = Bond.Orphaned; // ignore messages while we're unhooking
ManagedWndProcTracker.UnhookHwndSubclass(this);
// unhook, the Win32 way
try
{
UnsafeNativeMethods.CriticalSetWindowLong(_hwndHandleRef, NativeMethods.GWL_WNDPROC, _oldWndProc);
}
catch (System.ComponentModel.Win32Exception e)
{
if (e.NativeErrorCode != 1400) // ERROR_INVALID_WINDOW_HANDLE
{
throw;
}
}
// clear our state
_bond = Bond.Detached;
_oldWndProc = IntPtr.Zero;
_attachedWndProc = null;
_hwndAttached = IntPtr.Zero;
_hwndHandleRef = new HandleRef(null, IntPtr.Zero);
// un-Pin this object.
// Note: the GC is free to collect this object at anytime
// after we have freed this handle - that is, once all
// other managed references go away.
//AvDebug.Assert(_gcHandle.IsAllocated, "External GC handle has not been allocated.");
if (null != _gcHandle)
{
_gcHandle.Free();
}
return(true);
}