I'm trying to code up an async image downloader. I use NSURLConnection to get the data into an NSMutableData and use that data once it is complete to initialize a UIImage.
I checked the bytes and it downloads the entire image correctly (right number of bytes at least), however; when I call
[UIImage imageWithData:data]
and then check the properties of the image, it is zero width and a garbage number for height, in fact, same number no matter what the image is. I tried with bunch of different images, png, jpg, different urls, it always downloads the image completely but UIImage can't initialize with that data. What could I be doing wrong here?
Thanks.
Code is really as you'd expect it to look like:
Connection Delegate:
-(void)connectionDidFinishLoading:(NSURLConnection*)theConnection {
[[ImageManager sharedInstance] dataDownloadedBy:self]; }
ImageManager:
-(void)dataDownloadedBy:(WebConnection *)connection{
WebImage *image = [[WebImage alloc] initWithLink:connection.url];
[image setImageFromData:connection.data];
[images addObject:image];
[connection release];}
WebImage:
-(void)setImageFromData:(NSMutableData *)data{
image = [[UIImage alloc] initWithData:data];}
First, I'm sure the UIImage will not initialize with garbage data. The constructor initWithData analyzes the data to determine the file format. If your data is corrupted, the image returned will be nil. Check this at first.
-(void)dataDownloadedBy:(WebConnection *)connection{
WebImage *image = [[WebImage alloc] initWithLink:connection.url];
[image setImageFromData:connection.data];
if (image.image != nil) { [images addObject:image]; }
[connection release];
}
Second, make sure you append the data during the download process. Here is the callback method:
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[self.receivedData appendData:data];
}
Finally, your code must absolutely includes the second case: a download failure.
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
[connection release];
}
Your problem description lacks some important pieces of code.
The URLCache demo from Apple is a very good project to understand async image download.
http://developer.apple.com/iphone/library/samplecode/URLCache/Introduction/Intro.html
I hope this will help you!
I can't tell what is wrong, it could be you don't use the release properly, say i don't know why you release connection at the end of dataDownloadedBy, it is supposed to be image ?
it could help if you post more your code here.
I used to do the same thing, you can have a look the post here
http://blog.163.com/lionyue#126/blog/static/1079307120096895433277/
Hope it helps
If initWithData is failing, most likely the image data you're getting is corrupt. You should save it to a file like this:
[data writeToFile:#"/tmp/foo.jpg" atomically:NO];
and then try to open it in Preview.app.
a different problem, but that gives teh same painful error is if You ask for a file that is not reachable: HTTP server will give back error 404 message, your code read that bytes (they are NOT valid bytes for an image, AND You will got NIL.
Related
I am having trouble saving a photo into core data. I am trying to save it as an attribute set to 'Transformable' in an Entity. I have seen various discussions on this on SO and the consensus seems to be that in iOS5 and above, I don't need to use a coder as UIImage now conforms to NSCoding. I am getting an error when I try and save Core Data. Please see below the code I am using to save the photo...
- (void) imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
NSString *mediaType = [info objectForKey: UIImagePickerControllerMediaType];
UIImage *originalImage, *editedImage, *imageToSave;
// Handle a still image capture
if (CFStringCompare ((CFStringRef) mediaType, kUTTypeImage, 0) == kCFCompareEqualTo) {
editedImage = (UIImage *) [info objectForKey:UIImagePickerControllerEditedImage];
originalImage = (UIImage *) [info objectForKey:UIImagePickerControllerOriginalImage];
if (editedImage) {
imageToSave = editedImage;
} else {
imageToSave = originalImage;
}
// Convert image to Data for entry into Core Data
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(imageToSave)];
// Add image to Core Data
myEntity.attribute = imageData;
NSError *error = nil;
if (![managedObjectContext save:&error]) {
NSLog(#"Error when saving core data");
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
}
[[picker parentViewController] dismissModalViewControllerAnimated: YES];
[picker release];
}
I agree to Joseph's answer. But looking at Apple's recommendation for storing image if your image is(Courtesy - Marcus S. Zarra's answer here):
Less than 100K;store as a binary property in your main table
Less than 1M; store as a binary property in a ancillary table to avoid over fetching
Greater than 1M; store on disk and store its file path in the Core Data table.
From your code what I see is you are trying to save image taken from camera to Core Data. We know images taken from Phone/iPad camera are approx 2.5 Mbs nowadays. So it is quite possible that you will get performance issues. So I would advice you to store image in a document directory and save it's path as NSString in your entity. It will be a more efficient way.
I have done this many times. Change the storage type from transformable to Binary Data and you should be fine.
You also want to keep a couple of things in mind. If the image is small (1MB or less), there should be no issue storing it in your main entity. If it is larger, you should have the image stored in an entity by itself for performance reasons. If the image is very large, you may want to consider storing it off in the documents directory like anonymous suggests above.
i need to download large pdf from web and i created a progress bar controller.
But, how i set max progress value it i don't know the pdf size before downloading?
Is there a way to get file size and use it to increment progress bar?
I'm using
myPDFremoteUrl = "http://www.xasdaxxssxx.pdf";
- (float) getFileSize {
NSFileManager *man = [[NSFileManager alloc] init];
NSDictionary *attrs = [man attributesOfItemAtPath: myPDFremoteUrl error: NULL];
UInt32 result = [attrs fileSize];
return (float)result;
}
but i don't able to check remote size in this way...
any idea?
Thanks
I would use ASIHTTPRequest for your data retrieval. It has progress monitoring built in.
If you really want to stick with what you've got, you can look at the HTTP header. It has a property called "Content-Length" that will help you out.
Good luck.
ASIHTTPRequest has a downloadProgressDelegate that can handle this for you- its very easy to use.
Solved.
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
dimensione = (float)[response expectedContentLength];
NSLog(#"content-length: %f bytes", dimensione);
}
I forget didReceiveResponse!
good.
Is there any way I can convert the value of a [NSData bytes] to a float so that I can add it to a progress bar?
Thanks,
Kevin
In a nutshell: [data length]
Here is the snippet of how the download bar I use works.
// Can get called numerous times during download process
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
// Accumulate incoming data into mutable data object
[fileData appendData:data];
byteCount += [data length];
float progress = byteCount/(mapToDownload.fileSize);
[self performSelectorOnMainThread:#selector(updateProgress:) withObject:[NSNumber numberWithFloat:progress] waitUntilDone:NO];
}
Let me know if you need more information.
[Added Oct 26 to address your other question:]
I have not worked with NSStream. My example is from an asynchronous NSURLConnection example. Therefore, let's ignore my previous code example.
You mentioned that you have [NSData bytes]. [NSData length] should return you how much data you have. Assuming you know the size to be downloaded then:
float progressPercentage = [yourNSData length]/knownFileSize;
should give you the percentage needed to update the progress bar. You could then set your progress bar:
[yourProgressBar setProgress:progressPercentage];
I've been using NSURLConnection to do a HTTP post to establish the connection. I've also implemented the didReceiveData delegate to process incoming bytes as they become available.
As incoming data comes in via didReceiveData, I add the NSData to a data buffer and try parsing the bytesteam if enough data has come in to complete a message segment. I'm having a hard time managing the data buffer (NSMutableData object) to remove bytes that have been parsed to structs. Was curious if there's an easier way. My didReceiveData delegate is below.
It works, but I don't think I'm managing memory correctly after I copy the message segment (currMsg) out of the responseData buffer and call processMsg. I get double free errors when running under the Simulator -- the program doesn't crash.
NSMutableData/NSData provide methods for appending bytes to the end but I didn't see any methods for removing bytes from the beginning (bytes representing whats already been parsed. I would appreciate some advice on how to best remove the parsed bytes from the responseData buffer. I come from a mostly C background so I'm not sure if there are better ways of manipulating the NSData bytes pointer. I'd like to avoid copying if possible -- just want to process a portion of the responseData buffer and leave the rest in responseData for next time enough bytes are in it for parsing.
Thanks
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
NSData *tmpBuffer = nil;
NSInteger currMsgSize = 10;
[responseData appendData:data];
NSInteger rspDataLen = [responseData length];
while(rspDataLen >= 10) {
currMsg = [[NSData alloc] initWithBytesNoCopy:(void *)[responseData bytes] length:currMsgSize];
[self processMsg:currMsg];
[currMsg release];
[responseData getBytes:tmpBuffer range:NSMakeRange(currMsgSize, rspDataLen - currMsgSize)];
[responseData release];
responseData = [[NSMutableData alloc] initWithBytesNoCopy:(void *)tmpBuffer length:rspDataLen - currMsgSize];
rspDataLen = rspDataLen - currMsgSize;
}
}
Where do you allocate the first responseData?
What is [self processMsg:currMsg] doing with the data? If it is expecting the data to be around after -processMsg: returns, and it isn't explicitly making a copy, then you are in trouble.
Infact, unless you have finished with the received data before didReceiveData: returns, you need to make a copy of it somewhere, which isn't visible in the code shown.
You need to allocate the storage for tempBuffer, not pass in an uninitialised pointer;
You should look probably for a pre-rolled implementation of a simple ring buffer. There are plenty around.
I'm trying to download several images in response to a single http request. On the server side (java) I'm using oreilly multipart response and I'm getting my datas in my iPhone Simulator in didReceiveData (approximately one call for each image) after a call to didReceiveResponse (approximately one call for each image as well) in my delegate.
The problem is this approximately... Has anyone ever managed to handle correctly multipart/x-mixed-re with iPhone SDK ? If yes what is the best strategy here ? Should I play with the expected length ? on server side ? on client side ? should I wait until I've received everything... mmmh that doesn't even seen enough as the calls to didReceiveData happens in a random order (I'm asking picture1,picture2 and I'm sometimes receiving picture2,picture1 even though the order is respected on server side !). Should i temporize between pictures on server side ?
Or should I drop multipart/x-mixed-replace ? what would be the easiest then ?
That's a lot of questions but I'm really stuck here ! Thanks for you help !
I'm not sure what your final use for the images is, but the intended purpose of the multipart/x-midex-replace content type is for each received part to completely replace the previously received responses. Think of it like frames of a video; only one picture is displayed at a time and the previous ones are discarded.
Temporizing is almost never a foolproof solution. Especially on the iPhone you're going to encounter an unimaginable variety of network situations and relying on a magic number delay between frames will probably still fail some of the time.
Since you have control of the server, I'd recommend dropping the multipart. Make sure when you are sending multiple requests to the server that you don't block the main thread of your iPhone app. Use NSOperations or an alternative HTTP library (like ASIHTTPRequest) to make your image fetch operations asynchronous.
I did that successfully using this code. The important thing is to create 2 buffers to receive your data. If you use only one you will have some double access problems (stream access and jpg CODEC access) and corrupted JPG data.
Do not hesitate to ask me for more details.
- (IBAction)startDowload:(id)sender {
NSURL *url = [NSURL URLWithString:#"http://210.236.173.198/axis-cgi/mjpg/video.cgi?resolution=320x240&fps=5"];
NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];
[req setHTTPMethod:#"GET"];
/*
I create 2 NSMutableData buffers. This points is very important.
I swap them each frame.
*/
receivedData = [[NSMutableData data] retain];
receivedData2 = [[NSMutableData data] retain];
currentData = receivedData;
urlCon = [[NSURLConnection alloc] initWithRequest:req delegate:self];
noImg = YES;
frame = 0;
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSHTTPURLResponse *)response
{
// this method is called when the server has determined that it
// has enough information to create the NSURLResponse
// it can be called multiple times, for example in the case of a
// redirect, so each time we reset the data.
// receivedData is declared as a method instance elsewhere
UIImage *_i;
#try
{
_i = [UIImage imageWithData:currentData];
}
#catch (NSException * e)
{
NSLog(#"%#",[e description]);
}
#finally
{
}
CGSize _s = [_i size];
[imgView setImage:_i];
[imgView setNeedsDisplay];
[[self view] setNeedsDisplay];
}
/*
Buffers swap
*/
if (currentData == receivedData)
{
currentData = receivedData2;
}
else
{
currentData = receivedData;
}
[currendData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// append the new data to the currentData (NSData buffer)
[currendData appendData:data];
}