Need to capture screen without delay - ios

Question

So guys I'm using this function to take a picture of the UIWebView which loading an e-book and display it while the user render the pages
-(UIImage*)captureScreen:(UIView*) viewToCapture
{
UIGraphicsBeginImageContextWithOptions(viewToCapture.bounds.size, viewToCapture.opaque, 0.0);
[viewToCapture.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return viewImage;
}
but the problem there is a delay (0.5 second) happened to get the image .. when i test in the time profiler the instruments point to this line [viewToCapture.layer renderInContext:UIGraphicsGetCurrentContext()]; as the one which causing the delay .. so any advice , suggestion how could I come over this delay.
Thanks in advanced.
Notes :
1.Im using UIPageController for the book effect.
2.to check what I have tried please check this link

Answer 1

The best way of solving this is to use delegates. Meaning that if you tell a delegate method to make the image, it can do it in the background and tell your view "Hey, now I got you an image for XXX" (depending on how you implement it.
This way you can load your view with the e-books in it and just show a loader in the middle of the book with a default background. When the image is done, you update the view for the book with the correct image and remove the loader.
Much like how Apple's iBooks and any other good application does.
Example from one of my own projects (adapted to your need, yet for use in UITableViewController):
BookDelegate.h
#import <Foundation/Foundation.h>
#class Book;
#protocol BookDelegate <NSObject>
#optional
- (void)didRecieveImageForBook:(NSString*)imagePath indexPath:(NSIndexPath*)indexPath;
#end
Book.h
#import <Foundation/Foundation.h>
#import "BookDelegate.h"
#interface Book : NSOperation <NSObject>
{
id <BookDelegate> delegate;
SEL didRecieveImageForBookSelector;
}
#property (strong, nonatomic) id delegate;
#property (assign) SEL didRecieveImageForBookSelector;
- (NSString*)getBookImageForBookId:(int)BookId externalRefference:(NSString*)url indexPath:(NSIndexPath*)indexPath;
- (id)delegate;
// Delegate methods
- (void)didRecieveImageForBook:(NSString*)imagePath indexPath:(NSIndexPath*)indexPath;
#end
Book.m
#import "Book.h"
#import <objc/runtime.h>
#implementation Book
static char kAssociationKey;
#synthesize didRecieveImageForBookSelector;
#synthesize delegate;
- (id)init
{
if (self = [super init])
{
[self setDidRecieveImageForBookSelector:#selector(didRecieveImageForBook:indexPath:)];
}
return self;
}
#pragma mark -
#pragma mark The default delegate functions
- (void)didRecieveImageForBook:(NSString*)imagePath indexPath:(NSIndexPath*)indexPath
{
NSLog(#"********************************************************");
NSLog(#"*** PLEASE IMPLEMENT THE FOLLOWING DELEGATE FUNCTION ***");
NSLog(#"*** didRecieveImageForBook:indexPath: ***");
NSLog(#"********************************************************");
}
#pragma mark -
#pragma mark Function for fechting images
// This method is not adapted to what YOU need, but left my code here in case it might help you out.
- (NSString*)getBookImageForBookId:(int)bookId externalRefference:(NSString*)url indexPath:(NSIndexPath*)indexPath
{
NSString *ext = [[url lastPathComponent] pathExtension];
NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *imagePath = [documentsPath stringByAppendingPathComponent:[NSString stringWithFormat:#"%#%d.%#", APP_BookIMAGEPEFIX, BookId, ext]];
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:imagePath];
if (fileExists)
{
return imagePath;
}
else {
NSURL *theUrl = [NSURL URLWithString:url];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:theUrl];
[request setDidFinishSelector:#selector(BookImageFetched:)];
[request setDidFailSelector:#selector(processFailed:)];
[request setTimeOutSeconds:60];
[request setDownloadDestinationPath:imagePath];
[request setDelegate:self];
[request startAsynchronous];
objc_setAssociatedObject(request, &kAssociationKey, indexPath, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
return #"";
}
}
- (void)BookImageFetched:(ASIHTTPRequest *)request
{
NSIndexPath *indexPath = objc_getAssociatedObject(request, &kAssociationKey);
NSString *imagePath = request.downloadDestinationPath;
[[self delegate] performSelector:self.didRecieveImageForBookSelector withObject:imagePath withObject:indexPath];
}
#pragma mark -
#pragma mark delegate functions
- (id)delegate
{
return delegate;
}
- (void)setDelegate:(id)newDelegate
{
delegate = newDelegate;
}
#pragma mark -
#end

Answer 2

You could use GCD - I noticed a a step missing from the GCD in the link you gave. This is what I use to asynchronously get an image and notify when its ready and it works fine:
dispatch_queue_t concurrent = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(concurrent, ^{
__block UIImage *image = nil;
dispatch_sync(concurrent, ^{
//put code to grab image here
});
dispatch_sync(dispatch_get_main_queue(), ^{
//this gets called when the above is finshed
//you should also check if the image is nil or not
});
});
hope it helps
for the record - I use this for taking UIView snapshots and always try to put my target inside a parentview even if it is temporarily - it seems to speed it up.
UIGraphicsBeginImageContextWithOptions(self.bounds.size, YES, 0.0);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
not sure if it helps or if you are using the same approach. I hope you solve this soon :)