The GDI+ flat interface (gdiplusflat.h) declares a function
GdipCreateStreamOnFile
How is that stream supposed to be closed?
By calling pStream->Release().
Related
I have the following code that performs a background operation (scan_value) while updating a progress bar in the ui (progress). scan_value iterates over some value in obj, emitting a signal (value_changed) each time that the value is changed. For reasons which are not relevant here, I have to wrap this in an object (Scanner) in another thread. The Scanner is called when the a button scan is clicked. And here comes my question ... the following code works fine (i.e. the progress bar gets updated on time).
# I am copying only the relevant code here.
def update_progress_bar(new, old):
fraction = (new - start) / (stop - start)
progress.setValue(fraction * 100)
obj.value_changed.connect(update_progress_bar)
class Scanner(QObject):
def scan(self):
scan_value(start, stop, step)
progress.setValue(100)
thread = QThread()
scanner = Scanner()
scanner.moveToThread(thread)
thread.start()
scan.clicked.connect(scanner.scan)
But if I change the last part to this:
thread = QThread()
scanner = Scanner()
scan.clicked.connect(scanner.scan) # This was at the end!
scanner.moveToThread(thread)
thread.start()
The progress bar gets updated only at the end (my guess is that everything is running on the same thread). Should it be irrelevant if I connect the signal to a slot before of after moving the object receiving object to the Thread.
It shouldn't matter whether the connection is made before or after moving the worker object to the other thread. To quote from the Qt docs:
Qt::AutoConnection - If the signal is emitted from a different
thread than the receiving object, the signal is queued, behaving as
Qt::QueuedConnection. Otherwise, the slot is invoked directly,
behaving as Qt::DirectConnection. The type of connection is
determined when the signal is emitted. [emphasis added]
So, as long as the type argument of connect is set to QtCore.Qt.AutoConnection (which is the default), Qt should ensure that signals are emitted in the appropriate way.
The problem with the example code is more likely to be with the slot than the signal. The python method that the signal is connected to probably needs to be marked as a Qt slot, using the pyqtSlot decorator:
from QtCore import pyqtSlot
class Scanner(QObject):
#pyqtSlot()
def scan(self):
scan_value(start, stop, step)
progress.setValue(100)
EDIT:
It should be clarified that it's only in fairly recent versions of Qt that the type of connection is determined when the signal is emitted. This behaviour was introduced (along with several other changes in Qt's multithreading support) with version 4.4.
Also, it might be worth expanding further on the PyQt-specific issue. In PyQt, a signal can be connected to a Qt slot, another signal, or any python callable (including lambda functions). For the latter case, a proxy object is created internally that wraps the python callable and provides the slot that is required by the Qt signal/slot mechanism.
It is this proxy object that is the cause of the problem. Once the proxy is created, PyQt will simply do this:
if (rx_qobj)
proxy->moveToThread(rx_qobj->thread());
which is fine if the connection is made after the receiving object (i.e. rx_qobj) has been moved to its thread; but if it's made before, the proxy will stay in the main thread.
Using the #pyqtSlot decorator avoids this issue altogether, because it creates a Qt slot more directly and does not use a proxy object at all.
Finally, it should also be noted that this issue does not currently affect PySide.
My problem was solved by movinf the connection to the spot where the worker thread is initialized, in my case because I am accessing an object which only exists after instantiation of my Worker Object class which is in another thread.
Simply connect the signal after the self.createWorkerThread()
Regards
This has to do with the connection types of Qt.
http://pyqt.sourceforge.net/Docs/PyQt5/signals_slots.html#connect
http://qt-project.org/doc/qt-4.8/qt.html#ConnectionType-enum
In case both objects live in the same thread, a standard connection type is made, which results in a plain function call. In this case, the time consuming operation takes place in the GUI thread, and the interface blocks.
In case the connection type is a message passing style connection, the signal is emitted using a message which is handled in the other thread. The GUI thread is now free to update the user interface.
When you do not specify the connection type in the connect function, the type is automatically detected.
I have an HtmlTextWriter object (theWriter) being passed into a method. This method is in the middle tier. I'd like to read the contents of the theWriter in debug mode. The method is:
protected override void Render (HtmlTextWriter theWriter) {...}
which inherits from Panel:WebControl.
I've tried
theWriter.Flush();
theWriter.InnerWriter.ToString();
but that only outputs the object type: "System.Web.HttpWriter". I've seen some examples use methods on the Response object. But I don't have access to Response in this layer. Any ideas?
The InnerWriter is a TextWriter-derived class, which writes to a stream. You will have to open that stream and read data from it. Whether you can open and read from that stream is an open question, and depends very much on what type of stream it is.
So to use your example, theWriter.InnerWriter is an object derived from TextWriter. But you don't know what kind, and TextWriter itself doesn't expose the underlying stream.
Now, if InnerWriter is a StreamWriter, then you might be able to write:
var sWriter = theWriter.InnerWriter as StreamWriter;
var stream = sWriter.BaseStream;
var savePosition = stream.Position;
stream.Position = 0;
// now, you can read the stream
// when you're done reading the stream, be sure to reset its position
stream.Position = savePosition;
You have to be very careful, though. If you get the base stream and then open it with a StreamReader, closing the StreamReaderwill close the underlying stream. Then your HtmlTextWriter will throw an exception the next time you try to write to it.
It's also possible that you won't be able to read the stream. If the base stream is a NetworkStream, for example, you can't read it. Or it could be a FileStream that was open for write only. There's no good general way to do this, as it entirely depends not only on the specific TextWriter-derived class, but also on the stream that the TextWriter is writing to.
For example, the HtmlTextWriter could be writing to a StreamWriter, which is connected to a BufferedStream connected to a GZipStream, which finally writes to a MemoryStream.
So, in general, I'd recommend that you look for some other solution to your problem. Unless you know for sure what the underlying stream is, and that you can read it ... and that things won't change on you unexpectedly.
I am using RemoteObjects to call ZendAMF PHP from Flex/Flash Builder 4.6. I want to stop or abort a method call before it sends the request to the server based on an event or similar.
I have a class where I create and store all the RemoteObjects - for example:
activityLogService = new RemoteObject("zend");
activityLogService.endpoint=endpointServer;
activityLogService.addEventListener(FaultEvent.FAULT,faultHandler);
Then later I can simply call this object:
remotingService.activityLogService .getRecords();
I am trying to find a way in my remotingService object to stop the request - and not send anything to the server - for example if some variables are not set properly.
I noticed there is an invoke event:
activityLogService.addEventListener(InvokeEvent.INVOKE,invokeHandler);
However, I can not tell if that's going to stop things at the proper point, or if it's even possible to actually STOP the request - if so, how?
Thanks!
Check out this question
Flex : Is it possible to stop a remote call?
If you're using a RemoteObject you should be able to call
getOperation() method and then cancel() on the corresponding
operation.
I'm facing a practical problem with Qt. I'm using a class that communicates with QLocalSocket to another process (pipes/unix sockets) and I need to do that communication before other events occur, that is before app.exec() starts (or more precisely,as soon as app starts). The class that I'm using needs an eventloop so it does not work if I call the class methods before an event loop is started. There is any way to start something when the event loop is ready? I thought of making a hidden event-only window and do my duties in the hidden window constructor, and stablish this window as toplevel.
Basically, I need this local-socket communication task to start as soon as the event loop becomes available.
Any ideas?
Thank you.
You could start a separate eventloop, using QEventLoop, before calling QApplication::exec(). You should emit a "done" signal from your class and connect that to the QEventLoop quit() slot, or use an existing signal provided in the Qt class you're using.
Here's a simple example fetching a webpage using QNetworkAccessManager:
app = QtCore.QCoreApplication([])
manager = QtNetwork.QNetworkAccessManager()
req = QtNetwork.QNetworkRequest(QtCore.QUrl("http://www.google.com"))
resp = manager.get(req)
eventloop = QtCore.QEventLoop()
eventloop.connect(resp, QtCore.SIGNAL('finished()'), QtCore.SLOT('quit()'))
eventloop.exec_() # this will block until resp emits finished()
print resp.readAll()
app.exec_()
While this might suit your needs, I couldn't quite understand why you can't simply do whatever business you have prior to calling show() on your window, once that's done, call show().
If you just need to start the communications before everything else, you can simply use a single-shot timer with 0ms delay:
QTimer::singleShot(0, commsInstancePtr, SLOT(startCommunication()));
If you need your operations to actually finish before doing everything else, Daniel's solution might be more suitable.
Currently I'm working on an application (Flex) which heavily uses external SWFs.
I'd like to create a static method which takes a filename as an argument and returns SWF wrapped in some other class.
public static function getSWFWrapperFromFile(path:string):SWFWrapper {
var loader:SWFLoader = new SWFLoader();
loader.addListener(Event.COMPLETE, onLoad);
loader.load(path);
// If I create new SWFWrapper object here and try to assign it the loader.content I get null reference
}
However, with this approach I'm not able to encapsulate logic in one function, because of non-blocking load() and the need of onLoad handler. Is there possibility to force a delay after calling load method? Or mayber there is another, better way?
Thank you,
Alonzo
The display list is well-designed for asynchronous loading. You'll notice that Loader is a DisplayObject-derived class and thus can be placed directly in the display list. When its content is loaded it will be a child of the Loader. Thus, if SWFWrapper is DisplayObject-derived, you can simply do the following at the end of your code:
var wrapper:SWFWrapper = new SWFWrapper();
wrapper.addChild(loader);
return wrapper;
You need to wait until your Loader object has completed. Try adding in an event handler. Yes, the whole thing gets murky after a point of time when you have multiple loaders and and have to wait till the last one has completed. But that's the way it is if you are going to use SWFLoader.
In flash you cannot block in a method - you always have to use the onLoad handler for loading data. (The as3 execution model is single threaded, if you block in a method the rest of the program will not get executed)
Like others said, you can't do that. However, take a look at the BulkLoader AS3 library, which takes the burden of managing multiple loaders simultaneously and waiting for their completion, off your shoulder. It is well documented, and requires only a few lines to use.