I need to continue writing to the same file using a file output stream, However I'm implementing the program using a javafx GUI from different windows. but:
Since you can not access a global variable without intializing the stream as final I have to make it final however,
Since I have to wrap the the Stream in a try catch, the variable is not recognised as initialised.
I was previously intialising in method like this
eW = outputFactory .createXMLEventWriter(new FileOutputStream("File.txt"));
However, that obivously overwrites the same file when you write the same statement again.
So essentially my question is, how can you set a final variable that needs to be surrounded in a try catch?
final File file = new File("File.txt");
final FileOutputStream fileOS = new FileOutputStream(file);
You don't need to initialize a variable as final to access it from different threads or objects. There are other ways to do it.
You can use a helper class, or even a helper thread. The second option is better in (the most common) case where you have more than 1 thread in your project. You can then use a normal try-catch block that has a (almost infinite) while loop inside, that checks a write queue and writes something when needed.
If you only use 1 thread and only append to a file, you may want to do just that - open the file to append, rather than overwrite. There's a boolean flag in the constructor.
You can take a look at the FileOutputStream(File file, boolean append) constructor, which would allow you to append to the end of the file rather than overwrite each time.
I do not know how you implemented it, but if you are writing to the same file from multiple windows, it might be easier to have a helper class which exclusively handles writing to file. This would allow you to centralize your File output code to one place making it easier to debug and maintain.
Related
I'm developing a bunch of Qt applications in C++ and they all use some modules (translation units) for common functionality that use Qt as well.
Whenever I convert a C string (implicit conversion) or C++ string object (fromStdString()) to a QString object, I expect the original data to be UTF-8 encoded and vice versa (toStdString()).
Since the default is Latin-1, I have to set the codec "manually" (in the init procedure of every one of my programs) to UTF-8:
QTextCodec::setCodecForCStrings(QTextCodec::codecForName("utf8"));
Not all of my modules have an init procedure. The ones containing a class do (I can put this line in the class constructor), but some modules just contain a namespace with lots of functions. So there's no place for setCodecForCStrings(). Whenever I convert from/to a QString implicitly (from within one of my modules), I rely on the codec being already set by the init procedure of the main program, which seems to be a rather bad solution.
Is there a reliable way to set the codec to UTF-8 in my modules, or will I just have to be very careful not to use implicit conversions at all (in my modules at least) and write something like std::string(q.toUtf8().constData()) instead of q.toStdString()?
This can be done using a class definition for an automatically instantiated singleton-similar class having some init code in its constructor:
class ModuleInit {
static ModuleInit *instance;
public:
ModuleInit() {
QTextCodec::setCodecForCStrings(QTextCodec::codecForName("utf8"));
}
};
ModuleInit * ModuleInit::instance = new ModuleInit(); // put this line in .cpp!
Putting this code anywhere into any project will set the text codec to UTF-8. You can, however, overwrite the text codec in the main() method, since the code above is executed even before the main() method.
With "anywhere" I of course mean places where it is syntactically allowed to. Put the class definition in some header file, and the instantiation in the appropriate .cpp file.
You can even put the whole code in one .cpp file, say moduleinit.cpp which you compile and link, but never explicitly use (there is no header file you could include...). This will also avoid accidental instantiations except the very first one and you will not have any problems with duplicate class names.
Note that you can't set the codec for C-strings in one particular file. Setting the codec using QTextCodec::setCodecForCString will set it application-wide!
in my project, I let users pick pictures using the FileReference class. I then load these pictures into their .data properties, using the load() function. After this I perform some local manipulation and send them to the server.
What I would like to do, is to be able to iterate over the picked FileReferences again, load them into .data properties, perform different manipulation and send them to the server once again. I know that I should be able to do this from user-invoked event, that is not an issue here.
Problem is, once the FileReference is loaded for the first time, I can not unload it in any way, and I can not keep the data for all the pictures in the memory because these are huge.
So I guess there is only one thing I can do, which is performing a DeepCopy on the FileReference... Then I could load the first version, scrap it and use the copy for the second 'run'.
I tried to use ObjectUtil.copy, but when I access e.g. .name property of the copy, it fails with:
Error #2037: Functions called in incorrect sequence, or earlier call was unsuccessful.
at flash.net::FileReference/get name()
the relevant snippet:
registerClassAlias("FileReference",FileReference);
masterFileList.addItem(FileReference(ObjectUtil.copy(fr_load.fileList[i])));
trace(masterFileList[i].name)
Is it true that there are some protected properties of FileReference class that prevent it from being copied? If it is so, can I sidestep this somehow? Or is there any other solution to my overall problem?
I appreciate any hints/ideas!
I was trying to do almost exactly what you were doing, and I almost gave up after reading some of the answers, but I think I found a way to do it. I've found that if you have a FileReference object and call load() multiple times, it will work, but the main problem is that you're keeping the high-res bytes in memory after the first load. As you've mentioned, for people who don't know image processing, this is a big no-no.
The way to get around this is that after your first load(), you need to call the cancel() method on FileReference. From my testing so far, it looks like that will clear out the bytes in the FileReference, and load() will still work if you call it a second time later. Just a word of caution, this isn't explicitly-defined behavior in the API, so it is definitely subject to change, but it may help get you where you need to go in the mean time.
Hope that helps.
you cant use a ObjectUtil.copy. This method is designed for copying only data objects (VO classes).
you should create a new FileReference and copy the porperties, one by one. Create a function to do this..
Would copying it to a temporary file and then uploading the temporary file work? For example
var fileRef:FileReference = new FileReference();
fileRef.browse();
......................
var tmpFile:File = File.createTempFile();
try {
var tmpFileStream:FileStream = new FileStream();
tmpFileStream.open(tmpFile, FileMode.WRITE);
trace("Opened file: " + tmpFile.nativePath);
tmpFileStream.writeBytes(fileRef.data);
trace("copied file");
} catch ( error:Error ) {
trace("Unable to open file " + tmpFile.nativePath + "\n");
throw error;
}
I'm thinking that the operation is completely disallowed, for good reasons. If you can duplicate a new FileReference through ActionScript code, then you'd also be able to manufacture a FileReference object through ActionScript code. Of course, that'd be a pretty bad security hole if you could force the upload of an arbitrary file.
Keeping a copy of the data in memory really isn't that bad of a solution. After all, it's temporary. The typical client computer should be able to manage a few hundred extra MB of data with no problem. It's certainly a better option than having their browser do two separate uploads, which is what your attempted solution would end up doing.
A completely different potential solution to this problem is to avoid image manipulation by Flex altogether. Flex could post the uploaded file directly to the server, and the server could do the image manipulation itself. Of course, if the manipulation is driven through user interactions, then that wouldn't work at all.
I want to get the system icon of a specified folder, but maybe the only way to retrieve the icon is to use SHGetFileInfo() method. The first parameter of SHGetFileInfo() method is a pointer of LPITEMIDLIST.
If I only have the absolute path of the folder, how can I get the pointer according to the path?
SHParseDisplayName().
Welcome to the wonderful world of PIDLs.
You can read more at Introduction to the Shell Namespace, but basically a PIDL is a Pointer to an item ID List. You can think of it as a linked list in contiguous memory, but instead of each node having a pointer to the next node, you instead have the cb member which is the Count of Bytes that are contained the item, so you can add that to the base address to get the next item. IDLists are terminated with an item with { cb = 0, abID = NULL }.
So, what's in these magic lits? Basically you don't care and can't know. Any IShellFolder implementation can create a new type of ID to represent its type of item in the shell namespace. The basic file system view that the Shell implements just stores the parts of the path in these lists, so you have something like "c:\" in the first one "Users\" in the next one, etc. In reality they are serialized structs (or classes) that may contain more data. But they can also represent printers, network shares, database searches (for search folders, stacks, etc).
All you really need to know is you can ask IShellFolders to give you a PIDL that represents the items they contain, and later on you can give that PIDL back to them, and other various Shell functions and interfaces, and they know how to deal with them. What SHParseDisplayName() basically does (I think) is go through the registry looking for all registered IShellFolder implementations and asks them if they know what to do with the string you pass in, and the first one to handle it makes the PIDL and gives it back.
My problem, simplified:
I have a dataGrid with a dataProvider "documents"
A column of the datagrid has a labelFunction that gets the project_id field of the document, and returns the project name, from a bindable variable "projects"
Now, I dispatch the events to download from the server the documents and the projects, but If the documents get downloaded before the projects, then the label function gives an error (no "projects" variable)
Therefore, I must serialize the commands being executed: the getDocuments command must execute only after the getProjects command.
In the real world, though, I have dozens of resources being downloaded, and those command are not always grouped together (so I can't for example execute the second command from the onSuccess() method of the first, because not always they must be executed together..)..
I need a simple solution.. I need an idea..
If I understand you correctly, you need to serialize the replies from the server. I have done that by using AsyncToken.
The approach: Before you call the remote function, add a "token" to it. For instance, an id. The reply from the server for that particular call will then include that token. That way you can keep several calls separate and create chains of remote calls.
It's quite cool actually:
service:RemoteObject;
// ..
var call:AsyncToken = service.theMethod.send();
call.myToken = "serialization id";
private function onResult(event:ResultEvent):void
{
// Fetch the serialization id and do something with it
var serId:String = event.token.myToken;
}
I've encountered a memory problem using FileReference.save(). My Flash application generates of a lot of data in real-time and needs to save this data to a local file. As I understand, Flash 10 (as opposed to AIR) does not support streaming to a file. But, what's even worse is that FileReference.save() duplicates all the data before saving it. I was looking for a workaround to this doubled memory usage and thought about the following approach:
What if I pass a custom subclass of ByteArray as an argument to FileReference.save(), where this ByteArray subclass would override all read*() methods. The overridden read*() methods would wait for a piece of data to be generated by my application, return this piece of data and immediately remove it from the memory. I know how much data will be generated, so I could also override length/bytesAvailable methods.
Would it be possible? Could you give me some hint how to do it? I've created a subclass of ByteArray, registered an alias for it, passed an instance of this subclass to FileReference.save(), but somehow FileReference.save() seems to treat it just as it was a ByteArray instance and doesn't call any of my overridden methods...
Thanks a lot for any help!
It's not something I've tried before, but can you try sending the data out to a php application that would handle saving the ByteArray to the server, much like saving an image to the server, so then you'd use URLLoader.data instead, using something like this:
http://www.zedia.net/2008/sending-bytearray-and-variables-to-server-side-script-at-the-same-time/
It's an interesting idea. Perhaps to start you should just add traces in your extended ByteArray to see how the FileReference#save() functions internally.
If it has some kind of
while( originalByteArray.bytesAvailable )
writeToSaveBuffer( originalByteArray.readByte() );
functionality the overrides could just truncate the original buffer on every read like you say, something like:
override function readByte() : uint {
var b : uint = super.readByte();
// Truncate the bytes (assuming bytesAvailable = length - removedBytes)
length = length - bytesAvailable;
return b;
}
On the other hand, if this now works I guess the original byte array would not be available afterwards in the application anymore.
(i havn't tested this myself, truncating might require more work than the example)