i'm working with VS2012, Windows Phone 8 SDK.
I need to access the camera natively.
I have sucesfully created a PhotoCaptureDevice instance by calling PhotoCaptureDevice::OpenAsync, then get the opened device - mCaptureObject - with the help of create_task() and task.then().
however,
mCaptureObject->Close()
caueses compile error.
CameraStream.cpp(xxx): error C2039: 'Close' : is not a member of Windows::Phone::Media::Capture::PhotoCaptureDevice'
here's a link to msdn:
PhotoCaptureDevice.Close()
i checked the photocapturedevice class declaration:
public : virtual unknown-type Close() new sealed = Platform::IDisposable::Dispose
Member of Windows::Phone::Media::Capture::PhotoCaptureDevice
Summary:
Releases resources that are associated with the capture device.
Any idea?
To call Close() on an object, you should invoke that object's destructor. This will happen naturally when the object no longer has references, or you can call delete mCaptureObject to force the destructor to run immediately. (If you do this while the object still has living references, those other references will be invalid and method calls should throw a DisconnectedException.)
Related
This question already has answers here:
How to use GetObject in VBScript
(2 answers)
Closed 3 years ago.
I recently got a small CG software package from my friend his father wrote about 30 years ago. It has a window where one can create and render some solid primitives. Interestingly, it has a VBA interface and I can in Excel (let’s call it TheSoftware) use Set app = CreateObject(“TheSoftware.Application”) to create such application (after setting app.Visible to True one can get the window on the screen)! However, the GetObject(, “TheSoftware.Application”) returns the “ActiveX component can’t create object” error. More surprisingly to me, the GetObject(“”, “TheSoftware.Application”) successfully creates the application! I have its source code in C++ about 900 KB that I can share, but just to be quick, has anyone had this issue before, or have a clue what may be the issue? I am no expert in C++, and the author passed away 4 years ago. I have seen the “opposite” problem of failing to create an object but OK when getting it, but not this one. Any idea is welcome, thanks!
GetObject(FName) opens a file or connects to a file if it already opened (and if class is specified use that class to open it) OR GetObject(,"Appname") connects to a running instance of an application. You are creating a blank file.
Visual Basic Scripting Edition
GetObject Function
See Also CreateObject Function
Requirements
Version 5
Returns a reference to an Automation object from a file.
GetObject([pathname] [, class])
Arguments
pathname
Optional; String. Full path and name of the file containing the object to retrieve.
If pathname is omitted, class is required.
class
Optional; String. Class of the object.
The class argument uses the syntax appname.objectype and has these
parts:
Use the GetObject function to access an Automation object from a file
and assign the object to an object variable. Use the Set statement to
assign the object returned by GetObject to the object variable. For
example:
Dim CADObject
Set CADObject = GetObject("C:\CAD\SCHEMA.CAD")
When this code is executed, the application associated with the
specified pathname is started and the object in the specified file is
activated. If pathname is a zero-length string (""), GetObject
returns a new object instance of the specified type. If the pathname
argument is omitted, GetObject returns a currently active object of
the specified type. If no object of the specified type exists, an
error occurs.
Some applications allow you to activate part of a file. Add an
exclamation point (!) to the end of the file name and follow it with a
string that identifies the part of the file you want to activate. For
information on how to create this string, see the documentation for
the application that created the object.
For example, in a drawing application you might have multiple layers
to a drawing stored in a file. You could use the following code to
activate a layer within a drawing called SCHEMA.CAD:
Set LayerObject = GetObject("C:\CAD\SCHEMA.CAD!Layer3")
If you don't specify the object's class, Automation determines the application to start and the object to activate, based on the file
name you provide. Some files, however, may support more than one class
of object. For example, a drawing might support three different types
of objects: an Application object, a Drawing object, and a Toolbar
object, all of which are part of the same file. To specify which
object in a file you want to activate, use the optional class
argument. For example:
Dim MyObject
Set MyObject = GetObject("C:\DRAWINGS\SAMPLE.DRW", "FIGMENT.DRAWING")
In the preceding example, FIGMENT is the name of a drawing application
and DRAWING is one of the object types it supports. Once an object is
activated, you reference it in code using the object variable you
defined. In the preceding example, you access properties and methods
of the new object using the object variable MyObject. For example:
MyObject.Line 9, 90
MyObject.InsertText 9, 100, "Hello, world."
MyObject.SaveAs "C:\DRAWINGS\SAMPLE.DRW"
Note Use the GetObject function when there is a current instance
of the object or if you want to create the object with a file already
loaded. If there is no current instance, and you don't want the
object started with a file loaded, use the CreateObject function.
If an object has registered itself as a single-instance object, only
one instance of the object is created, no matter how many times
CreateObject is executed. With a single-instance object, GetObject
always returns the same instance when called with the zero-length
string ("") syntax, and it causes an error if the pathname argument is
omitted.
Requirements Version 5
See Also CreateObject Function
© 2001 Microsoft Corporation. All rights reserved.
Build: Topic Version 5.6.9309.1546
Also these are the COM API calls that each form makes. From the Automation part of the COM docs.
CreateObject (“ProgID”)
CLSIDFromProgID
CoCreateInstance
QueryInterface to get IDispatch interface.
GetObject (“filename”, “ProgID”)
CLSIDFromProgID
CoCreateInstance
QueryInterface for IPersistFile interface.
Load on IPersistFile interface.
QueryInterface to get IDispatch interface.
GetObject (“filename”)
CreateBindCtx creates the bind context for the subsequent functions.
MkParseDisplayName returns a moniker handle for BindMoniker.
BindMoniker returns a pointer to the IDispatch interface.
Release on moniker handle.
Release on context.
GetObject (“ProgID”)
CLSIDFromProgID
GetActiveObject on class ID.
QueryInterface to get IDispatch interface.
Dim x As New interface
Find CLSID for interface.
CoCreateInstance
QueryInterface
I'm trying to write a DLL to access the C++-only method Windows.Devices.Bluetooth.BluetoothLEDevice.Close() from a C# app. I seem to be able to access the class, but Visual Studio will not build if I try to use that one method. It is shown in the member list that comes up as you type, and there is no Intellisense error, just the build error.
using namespace Windows::Devices::Bluetooth;
__declspec(dllexport) void CloseBleDeviceUnmanaged(BluetoothLEDevice^device)
{
if (device->ConnectionStatus == BluetoothConnectionStatus::Connected) //no complaints for a property
{
device->GetDeviceSelector(); //no complaints for a method either
device->Close(); //Error C2039 | 'Close': is not a member of 'Windows::Devices::Bluetooth::BluetoothLEDevice'
}
return;
}
How do I get this to at least build?
(edit: removed extraneous syntax problem as per Nico Zhu - MSFT's answer)
You don't need to do any of this to call Close from C# -- just put it in a using(...) block and it will dispose (close) the object for you automatically. If the lifetime of the objection doesn't lend itself well to a using block, you can simply call IDisposabe.Dispose() on it directly.
For the compiler error, this is documented in MSDN since you should never call Close from C++/CX:
Close methods aren't callable through Visual C++ component extensions (C++/CX) on Windows Runtime class instances where the class implemented IClosable. Instead, Visual C++ component extensions (C++/CX) code for runtime classes should call the destructor or set the last reference to null.
The parameter of CloseBleDeviceUnmanaged method is Value Type in your case. When you pass a parameter to the method. The parameter will generate a copy. And the original parameter has not been changed. Please pass the
reference type parameter like the follow.
void DevicesTool::CloseBleDeviceUnmanaged(Windows::Devices::Bluetooth::BluetoothLEDevice^device)
{
if (device->ConnectionStatus == BluetoothConnectionStatus::Connected)
{
device->GetDeviceSelector();
device->Close();
}
}
As for the Close method, I have reproduced the issue in my side(target platform version 16299), and I have report this to related team. Please pay attention to the thread update.
this is the source of the issue. My answer there was deleted with the hint to start a new question. So, here we go:
I want to pass the managed reference of this to unmanaged code. And then call the managed callback out of the unmanaged callback.
public ref class CReader
with a private field
private:
[...]
void *m_pTag;
[...]
In the constructor of the managed class I initialize the m_pTag like this:
m_pTag = new gcroot<CReader ^>(this);
Later, I pass this void *m_pTag to the unmanaged code. If the unmanaged callback is called, I'm casting the void *m_pTag back to managed reference and call the managed callback
(*(gcroot<CReader ^>*)pTag)->MANAGEDCALLBACKFUNCTION
and there is an exception thrown, if the DLL is used under another AppDomain. The Debugger stops in gcroot.h on line
// don't return T& here because & to gc pointer not yet implemented
// (T should be a pointer anyway).
T operator->() const {
// gcroot is typesafe, so use static_cast
return static_cast<T>(__VOIDPTR_TO_GCHANDLE(_handle).Target);
}
with Cannot pass a GCHandle across AppDomains.
My question is, what should I do?
Sincerly,
Sebastian
==================== EDIT ====================
I am now able to reproduce the problem. I've took some screenshots, to show the issue.
1st screenshot: constructor
snd screenshot: callback
The problem is, that the value-member of the struct gcroot in the callback is empty.
Thank you.
Sebastian
==================== EDIT ====================
Push.
The gcroot<> C++ class is a wrapper that uses the GCHandle class. The constructor calls GCHandle.ToIntPtr() to turn the handle into an opaque pointer, one that you can safely store as a member of an unmanaged struct or C++ class.
The cast then, later, converts that raw pointer back to the handle with the GCHandle.FromIntPtr() method. The GCHandle.Target property gives you the managed object reference back.
GCHandle.FromIntPtr() can indeed fail, the generic exception message is "Cannot pass a GCHandle across AppDomains". This message only fingers the common reason that this fails, it assumes that GCHandle is used in safe code and simply used incorrectly.
The message does not cover the most common reason that this fails in unsafe code. Code that invariably dies with undiagnosable exceptions due to heap corruption. In other words, the gcroot<> member of the C++ class or struct getting overwritten with an arbitrary value. Which of course dooms GCHandle.FromIntPtr(), the CLR can no longer find the handle back from a junk pointer value.
You diagnose this bug the way you diagnose any heap corruption problem. You first make sure that you get a good repro so you can trip the exception reliably. And you set a data breakpoint on the gcroot member. The debugger automatically breaks when the member is written inappropriately, the call stack gives you good idea why this happened.
I have looking at many threads about the exception "cannot pass a GCHandle across AppDomains" but I still don't get it....
I'm working with an RFID Reader which is driven by a DLL. I don't have source code for this DLL but only a sample to show how to use it.
The sample works great but I have to copy some code in another project to add the reader to the middleware Microsoft Biztalk.
The problem is that the process of Microsoft Biztalk works in another AppDomain. The reader handle events when a tag is read. But when I run it under Microsoft Biztalk I got this annoying exception.
I can't see any solution on how to make it work...
Here is some code that may be interesting :
// Let's connecting the result handlers.
// The reader calls a command-specific result handler if a command is done and the answer is ready to send.
// So let's tell the reader which functions should be called if a result is ready to send.
// result handler for reading EPCs synchronous
Reader.KSRWSetResultHandlerSyncGetEPCs(ResultHandlerSyncGetEPCs);
[...]
var readerErrorCode = Reader.KSRWSyncGetEPCs();
if (readerErrorCode == tKSRWReaderErrorCode.KSRW_REC_NoError)
{
// No error occurs while sending the command to the reader. Let's wait until the result handler was called.
if (ResultHandlerEvent.WaitOne(TimeSpan.FromSeconds(10)))
{
// The reader's work is done and the result handler was called. Let's check the result flag to make sure everything is ok.
if (_readerResultFlag == tKSRWResultFlag.KSRW_RF_NoError)
{
// The command was successfully processed by the reader.
// We'll display the result in the result handler.
}
else
{
// The command can't be proccessed by the reader. To know why check the result flag.
logger.error("Command \"KSRWSyncGetEPCs\" returns with error {0}", _readerResultFlag);
}
}
else
{
// We're getting no answer from the reader within 10 seconds.
logger.error("Command \"KSRWSyncGetEPCs\" timed out");
}
}
[...]
private static void ResultHandlerSyncGetEPCs(object sender, tKSRWResultFlag resultFlag, tKSRWExtendedResultFlag extendedResultFlag, tKSRWEPCListEntry[] epcList)
{
if (Reader == sender)
{
// Let's store the result flag in a global variable to get access from everywhere.
_readerResultFlag = resultFlag;
// Display all available epcs in the antenna field.
Console.ForegroundColor = ConsoleColor.White;
foreach (var resultListEntry in epcList)
{
handleTagEvent(resultListEntry);
}
// Let's set the event so that the calling process knows the command was processed by reader and the result is ready to get processed.
ResultHandlerEvent.Set();
}
}
You are having a problem with the gcroot<> helper class. It is used in the code that nobody can see, inside that DLL. It is frequently used by C++ code that was designed to interop with managed code, gcroot<> stores a reference to a managed object. The class uses the GCHandle type to add the reference. The GCHandle.ToIntPtr() method returns a pointer that the C++ code can store. The operation that fails is GCHandle.FromIntPtr(), used by the C++ code to recover the reference to the object.
There are two basic explanations for getting this exception:
It can be accurate. Which will happen when you initialized the code in the DLL from one AppDomain and use it in another. It isn't clear from the snippet where the Reader class object gets initialized so there are non-zero odds that this is the explanation. Be sure to keep it close to the code that uses the Reader class.
It can be caused by another bug, present in the C++ code inside the DLL. Unmanaged code often suffers from pointer bugs, the kind of bug that can accidentally overwrite memory. If that happens with the field that stores the gcroot<> object then nothing goes wrong for a while. Until the code tries to recover the object reference again. At that point the CLR notices that the corrupted pointer value no longer matches an actual object handle and generates this exception. This is certainly the hard kind of bug to solve since this happens in code you cannot fix and showing the programmer that worked on it a repro for the bug is very difficult, such memory corruption problems never repro well.
Chase bullet #1 first. There are decent odds that Biztalk runs your C# code in a separate AppDomain. And that the DLL gets loaded too soon, before or while the AppDomain is created. Something you can see with SysInternals' ProcMon. Create a repro of this by writing a little test program that creates an AppDomain and runs the test code. If that reproduces the crash then you'll have a very good way to demonstrate the issue to the RFID vendor and some hope that they'll use it and work on a fix.
Having a good working relationship with the RFID reader vendor to get to a resolution is going to be very important. That's never not a problem, always a good reason to go shopping elsewhere.
I am seeing this warning in my JNI code:
JNI WARNING: 0x44be7258 is not a valid JNI reference
I am assigning a LocalReference returned by FindClass method in JNI to my class member variable within the constructor:
Header:
...
jclass m_class;
Cpp:
m_class = env->FindClass( classSignature );
Does FindClass return a LocalReference and storing it in my class member variable is invalid?
From the Liang book, chapter 5.1.1 "Local References"
Most JNI functions create local references ... A local reference is valid only within the dynamic context of the native method that creates it, and only within that one invocation of the native method. All local references created during the execution of a native method will be freed once the native method returns.
Followed by an illegal code example which uses exactly your method FindClass. In other words, yes, FindClass returns a local reference. In the following chapter is an example of creating a global reference which is usable in the way you wanted. Don't forget to DeleteGlobalRef when you don't need it anymore. Otherwise JVM cannot GC it and your program will leak.