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Checking if UIGraphicsBeginImageContextWithOptions is supported

Answer 1

+4 A:

UIGraphicsBeginImageContextWithOptions is a C function, so you can't use Objective-C methods like -respondsToSelector: to test its existence.

You could, however, weak link the UIKit framework, and then check if UIGraphicsBeginImageContextWithOptions is NULL:

if (UIGraphicsBeginImageContextWithOptions != NULL) {
   UIGraphicsBeginImageContextWithOptions(...);
} else {
   UIGraphicsBeginImageContext(...);
}

KennyTM 2010-08-31 08:00:10

Thanks, are you sure I need to weaklink UIKit though ?

Gidogeek 2010-08-31 08:04:34

@Gido: No. You could use `dlsym`. But weak link is easiest.

KennyTM 2010-08-31 08:18:54

I weaklinked the UIKit framework and entered the code as you show it here. However on an iPhone running OS 3.0 it still manages to go through the IF statement instead of ending up in the else..

Gidogeek 2010-08-31 13:02:15

No other suggestions ?

Gidogeek 2010-09-01 10:35:24

The code currently looks like this: http://dl.dropbox.com/u/610806/backwardscompatability.pngThe code however ends up in the NSLog line on a iPhone 3G running 3.1.3 which does not have this method. What could I be doing wrong ?

Gidogeek 2010-09-01 13:23:16

@Gigo: Try `NSLog(@"%p", UIGraphicsBeginImageContextWithOptions)`?

KennyTM 2010-09-01 13:33:54

@KennyTM this prints out "0x0"

Gidogeek 2010-09-01 13:36:01

@Gidogeek: Odd, then the `if` line shouldn't pass, since `0 != NULL` is false obviously.

KennyTM 2010-09-01 13:38:18

@KennyTM that's what I figured.. but somehow it passes.. pulling out my hair over this.. what else could I try ?

Gidogeek 2010-09-01 13:40:58

@Gido: Try casting UIGraphicsBeginImageContextWithOptions to `void*`?

KennyTM 2010-09-01 14:01:10

@KennyTM sadly that didn't help either. Probably I should look for the problem elsewhere.. if all these people use it without trouble I should be doing something wrong in my setup. Probably something basic so I'll list some of the properties in my plist for my build target:* Base SDK: iPhone Device 4.0* C/C++ Compiler: LLVM compiler 1.5* iPhone OS Deployment Target: iPhone OS 3.1.3I have the before mentioned code in a category like so:@interface UIImage (Resizing)//the methods containing the version specific code@endCould this be cause of the problem ?

Gidogeek 2010-09-01 14:16:16

@Gido: Have you tried using GCC instead of LLVM?

KennyTM 2010-09-01 14:36:17

@KennyTM switching the compiler to GCC 4.2 actually worked.. how silly is that ? is this a bug ? Thanks anyway !

Gidogeek 2010-09-01 15:02:03

@Gido: Likely an optimizing-too-aggressively bug of LLVM. [Please file a bug report](http://llvm.org/docs/HowToSubmitABug.html).

KennyTM 2010-09-01 15:35:04

This worked perfectly for me. Thanks

Daniel Wood 2010-09-12 17:13:34

Answer 2

A:

I have the same problem. You could try testing the system version. This seems to work for me on the devices I tested.

char majorVersion = [[[UIDevice currentDevice] systemVersion] characterAtIndex: 0];
if (majorVersion == '2' || majorVersion == '3')
     UIGraphicsBeginImageContext(...);
else
     UIGraphicsBeginImageContextWithOptions(...);

Eric 2010-10-04 16:11:47

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