问题描述：今天Touch Team出Stupid测试版，安装20多台iPhone、iTouch、iPad，都可以安装。但是有一台iPhone（3.1.2）报错，不能安装。注：其他设备基本都在4.0以上。
问题分析：因为是调试安装，所以能看到报错信息，如下：
GNU gdb 6.3.50-20050815 (Apple version gdb-1518) (Sat Feb 12 02:56:02 UTC 2011)
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This GDB was configured as "--host=x86_64-apple-darwin --target=arm-apple-darwin".tty /dev/ttys000
target remote-mobile /tmp/.XcodeGDBRemote-16799-38
Switching to remote-macosx protocol
mem 0x1000 0x3fffffff cache
mem 0x40000000 0xffffffff none
mem 0x00000000 0x0fff none
[Switching to process 11779 thread 0x0]
[Switching to process 11779 thread 0x0]
sharedlibrary apply-load-rules all
warning: Unable to read symbols for /Library/MobileSubstrate/MobileSubstrate.dylib (file not found).
warning: Unable to read symbols for /Library/Frameworks/CydiaSubstrate.framework/Libraries/SubstrateLoader.dylib (file not found).
2011-09-27 17:40:14.990 FSStupid[2874:207] MS:Notice: Installing: com.flipscript.stupid [FSStupid] (478.52)
2011-09-27 17:40:15.368 FSStupid[2874:207] MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib
warning: Unable to read symbols for /Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib (file not found).
warning: Unable to read symbols for /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.1.3/Symbols/usr/lib/libsubstrate.dylib (file not found).
2011-09-27 17:40:17.131 FSStupid[2874:207] MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Multitasking.dylib
warning: Unable to read symbols for /Library/MobileSubstrate/DynamicLibraries/Multitasking.dylib (file not found).
2011-09-27 17:40:18.007 FSStupid[2874:207] *** -[UIWindow setRootViewController:]: unrecognized selector sent to instance 0x23fe20
2011-09-27 17:40:18.016 FSStupid[2874:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UIWindow setRootViewController:]: unrecognized selector sent to instance 0x23fe20'
2011-09-27 17:40:18.034 FSStupid[2874:207] Stack: (
843263261,
825818644,
843267069,
842763033,
842725440,
11685,
843742792,
843741800,
844074496,
844072508,
844071060,
860907492,
843011371,
843009055,
843738120,
843731504,
11481,
11404
)
terminate called after throwing an instance of 'NSException'
(gdb)
报错的语句是：
self.window.rootViewController = startViewController;
仔细查看报错信息，发现这句报错：-[UIWindow setRootViewController:]: unrecognized selector sent to instance。查看setRootViewController方法，发现需要4.0以上支持。
解决方案：把出错代码：
self.window.rootViewController = startViewController;
替换为：
if( [[[UIDevice currentDevice] systemVersion] compare:@"4.0" options:NSNumericSearch] == NSOrderedAscending )
[self.window addSubview:self.mainViewController.view];
else self.window.rootViewController = self.mainViewController;
一切ok了。