6

I tried below steps to capture screenshot.

CGSize imageSize = [[UIScreen mainScreen] bounds].size;
if (NULL != UIGraphicsBeginImageContextWithOptions) {
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
}
else
{
    UIGraphicsBeginImageContext(imageSize);
}
CGContextRef context = UIGraphicsGetCurrentContext();
@try {
    for (UIWindow * window in [[UIApplication sharedApplication] windows]) {
        if (![window respondsToSelector:@selector(screen)] || [window screen] == [UIScreen mainScreen]) {
            CGContextSaveGState(context);
            CGContextTranslateCTM(context, [window center].x, [window center].y);
            CGContextConcatCTM(context, [window transform]);
            CGContextTranslateCTM(context, -[window bounds].size.width*[[window layer] anchorPoint].x, -[window bounds].size.height*[[window layer] anchorPoint].y);

            dispatch_sync(dispatch_get_main_queue(), ^{
                LogInfo(@"before renderInContext on main thread");
                [[window layer] renderInContext:context];
                LogInfo(@"after renderInContext  on main thread");
            });

            CGContextRestoreGState(context);
        }
    }
}
@catch (NSException *exception) {
    LogInfo(@"catch NSException %@ in captureScreen",[exception name]);
}
@finally {

}
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

But sometimes crash, Crash Log:

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)    
Exception Subtype: KERN_INVALID_ADDRESS at 0x11bd70d8    
Triggered by Thread:  0    
Thread 0 Crashed:    
0   CoreGraphics                  0x2f9829ce argb32_image_mark_argb32 + 402
1   CoreGraphics                  0x2f9827d2 argb32_image_mark_image + 706
2   CoreGraphics                  0x2f97e126 argb32_image + 2106
3   libRIP.A.dylib                0x2fccbafa ripl_Mark + 14
4   libRIP.A.dylib                0x2fcd61ac RIPLayerBltImage + 728
5   libRIP.A.dylib                0x2fcc9862 ripc_RenderImage + 434
6   libRIP.A.dylib                0x2fcc816e ripc_DrawImage + 662
7   CoreGraphics                  0x2f97b6f8 CGContextDelegateDrawImage + 48
8   CoreGraphics                  0x2f97b57c CGContextDrawImage + 280
9   QuartzCore                    0x31dfa642 -[CALayer _renderForegroundInContext:] + 2266
10  QuartzCore                    0x31df976a -[CALayer renderInContext:] + 1222
11  QuartzCore                    0x31dfaa08 -[CALayer _renderSublayersInContext:] + 292
12  QuartzCore                    0x31df9782 -[CALayer renderInContext:] + 1246
13  QuartzCore                    0x31df98b4 -[CALayer renderInContext:] + 1552
14  QuartzCore                    0x31dfaa08 -[CALayer _renderSublayersInContext:] + 292
15  QuartzCore                    0x31df9782 -[CALayer renderInContext:] + 1246
16  UIKit                         0x32721322 -[_UIBackdropViewLayer renderInContext:] + 78
17  QuartzCore                    0x31dfaa08 -[CALayer _renderSublayersInContext:] + 292
18  QuartzCore                    0x31df9782 -[CALayer renderInContext:] + 1246
19  QuartzCore                    0x31dfaa08 -[CALayer _renderSublayersInContext:] + 292
20  QuartzCore                    0x31df9782 -[CALayer renderInContext:] + 1246
21  QuartzCore                    0x31dfaa08 -[CALayer _renderSublayersInContext:] + 292
22  QuartzCore                    0x31df9782 -[CALayer renderInContext:] + 1246
23  QuartzCore                    0x31dfaa08 -[CALayer _renderSublayersInContext:] + 292
24  QuartzCore                    0x31df9782 -[CALayer renderInContext:] + 1246
25  RuiKlasse                     0x00113598 0x8e000 + 546200
26  libdispatch.dylib             0x3a8cbb36 _dispatch_barrier_sync_f_slow_invoke + 66
27  libdispatch.dylib             0x3a8c5d3c _dispatch_client_callout + 20
28  libdispatch.dylib             0x3a8c86be _dispatch_main_queue_callback_4CF + 274
29  CoreFoundation                0x2f8cc674 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 4
30  CoreFoundation                0x2f8caf40 __CFRunLoopRun + 1304
31  CoreFoundation                0x2f8357a4 CFRunLoopRunSpecific + 520
32  CoreFoundation                0x2f835586 CFRunLoopRunInMode + 102
33  GraphicsServices              0x3476f6ce GSEventRunModal + 134
34  UIKit                         0x3219488c UIApplicationMain + 1132
35  RuiKlasse                     0x0024d46c 0x8e000 + 1832044
36  libdyld.dylib                 0x3a8daab4 start + 0

This issue doesn't happen every time, but it happens just enough to render my app unusable(crashed).I'm at my wit's end with this. Could anyone know how to fix it or give me some hints to investigate the problem?

further findings：

1.even though I run the entire code on main thread, this problem still happened. 2.KERN_INVALID_ADDRESS doesn't point to context. (I got the address of context and found that they were different)

Am I doing something wrong? How did you solved it?

Ying
  • 101
  • 5
  • That dispatch_sync into the main thread looks very odd. Any particular reason for doing that?. Or more to the point why isn't the entire setup & render inside the block instead of just the render call. – Warren Burton Oct 16 '14 at 06:45
  • @WarrenBurton thanks for your comment. At first, I didn't run renderInContext on main thread,but it caused crash and from crash log I knew I should not run it in background thread. – Ying Oct 16 '14 at 07:04
  • CGContextRef isn't thread safe so you can't do what you are doing. You need to place the entire chunk inside the block not just the render call. – Warren Burton Oct 16 '14 at 09:10
  • @WarrenBurton bad news... even though I placed the entire chunk inside the block, this problem still happened. Thank you all the same. – Ying Oct 17 '14 at 08:11
  • Check out what was done here: http://stackoverflow.com/questions/11253972/ipad-3-device-crash-with-renderincontext – bscazz11 Sep 16 '15 at 01:49
  • We were you attempting to draw a very large image into the context? – Jamie Forrest Mar 23 '16 at 13:09

0 Answers0