Löschen von Inhalten vom Gerät
Ein weiterer gängiger Vorgang, der von einer WPD-Anwendung durchgeführt wird, ist das Löschen von Inhalten von einem Speicherort auf dem Gerät.
Inhaltslöschvorgänge werden mithilfe der in der folgenden Tabelle beschriebenen Schnittstellen durchgeführt.
| Schnittstelle | Beschreibung |
|---|---|
| IPortableDeviceContent-Schnittstelle | Bietet Zugriff auf die Methoden zum Löschen von Inhalten. |
| IPortableDevicePropVariantCollection-Schnittstelle | Bietet Zugriff auf eigenschaftsspezifische Methoden. |
Die DeleteContentFromDevice-Funktion im Modul ContentTransfer.cpp der Beispielanwendung veranschaulicht, wie eine Anwendung Inhalte auf dem Gerät löschen kann. Vorgänge zum Löschen von Inhalten ähneln den Inhaltsübertragungsvorgängen sehr. Der einzige Unterschied besteht darin, dass die Anwendung während eines Löschvorgangs IPortableDeviceContent::D elete anstelle von IPortableDeviceContent::Move aufruft. (Eine Beschreibung der Aufgaben, die zum Aufrufen der Delete-Methode führen, finden Sie im Thema Verschieben von Inhalten auf dem Gerät .)
void DeleteContentFromDevice(
IPortableDevice* pDevice)
{
HRESULT hr = S_OK;
WCHAR szSelection[81] = {0};
CComPtr<IPortableDeviceContent> pContent;
CComPtr<IPortableDevicePropVariantCollection> pObjectsToDelete;
CComPtr<IPortableDevicePropVariantCollection> pObjectsFailedToDelete;
if (pDevice == NULL)
{
printf("! A NULL IPortableDevice interface pointer was received\n");
return;
}
// Prompt user to enter an object identifier on the device to delete.
printf("Enter the identifer of the object you wish to delete.\n>");
hr = StringCbGetsW(szSelection,sizeof(szSelection));
if (FAILED(hr))
{
printf("An invalid object identifier was specified, aborting content deletion\n");
}
// 1) get an IPortableDeviceContent interface from the IPortableDevice interface to
// access the content-specific methods.
if (SUCCEEDED(hr))
{
hr = pDevice->Content(&pContent);
if (FAILED(hr))
{
printf("! Failed to get IPortableDeviceContent from IPortableDevice, hr = 0x%lx\n",hr);
}
}
// 2) CoCreate an IPortableDevicePropVariantCollection interface to hold the object identifiers
// to delete.
//
// NOTE: This is a collection interface so more than 1 object can be deleted at a time.
// This sample only deletes a single object.
if (SUCCEEDED(hr))
{
hr = CoCreateInstance(CLSID_PortableDevicePropVariantCollection,
NULL,
CLSCTX_INPROC_SERVER,
IID_PPV_ARGS(&pObjectsToDelete));
if (SUCCEEDED(hr))
{
if (pObjectsToDelete != NULL)
{
PROPVARIANT pv = {0};
PropVariantInit(&pv);
// Initialize a PROPVARIANT structure with the object identifier string
// that the user selected above. Notice we are allocating memory for the
// PWSTR value. This memory will be freed when PropVariantClear() is
// called below.
pv.vt = VT_LPWSTR;
pv.pwszVal = AtlAllocTaskWideString(szSelection);
if (pv.pwszVal != NULL)
{
// Add the object identifier to the objects-to-delete list
// (We are only deleting 1 in this example)
hr = pObjectsToDelete->Add(&pv);
if (SUCCEEDED(hr))
{
// Attempt to delete the object from the device
hr = pContent->Delete(PORTABLE_DEVICE_DELETE_NO_RECURSION, // Deleting with no recursion
pObjectsToDelete, // Object(s) to delete
NULL); // Object(s) that failed to delete (we are only deleting 1, so we can pass NULL here)
if (SUCCEEDED(hr))
{
// An S_OK return lets the caller know that the deletion was successful
if (hr == S_OK)
{
printf("The object '%ws' was deleted from the device.\n", szSelection);
}
// An S_FALSE return lets the caller know that the deletion failed.
// The caller should check the returned IPortableDevicePropVariantCollection
// for a list of object identifiers that failed to be deleted.
else
{
printf("The object '%ws' failed to be deleted from the device.\n", szSelection);
}
}
else
{
printf("! Failed to delete an object from the device, hr = 0x%lx\n",hr);
}
}
else
{
printf("! Failed to delete an object from the device because we could no add the object identifier string to the IPortableDevicePropVariantCollection, hr = 0x%lx\n",hr);
}
}
else
{
hr = E_OUTOFMEMORY;
printf("! Failed to delete an object from the device because we could no allocate memory for the object identifier string, hr = 0x%lx\n",hr);
}
// Free any allocated values in the PROPVARIANT before exiting
PropVariantClear(&pv);
}
else
{
printf("! Failed to delete an object from the device because we were returned a NULL IPortableDevicePropVariantCollection interface pointer, hr = 0x%lx\n",hr);
}
}
else
{
printf("! Failed to CoCreateInstance CLSID_PortableDevicePropVariantCollection, hr = 0x%lx\n",hr);
}
}
}
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