转自：http://www.cocoachina.com/iphonedev/sdk/2010/0624/1749.html
很多应用里都要用到苹果iPhone自带的三轴感应器（加速度传感器），希望下面这段代码例子能为您使用iPhone三轴感应器打开思路。
#include <IOKit/IOKitLib.h>
#include <CoreFoundation/CoreFoundation.h> typedef struct { } *IOHIDEventSystemRef; typedef struct { } *IOHIDEventRef; float IOHIDEventGetFloatValue (IOHIDEventRef ref, int param ); void handleHIDEvent ( int a, int b, int c, IOHIDEventRef ptr ) { int type = IOHIDEventGetType (ptr ); if ( type == 12 ) { float x, y,z; x = IOHIDEventGetFloatValue (ptr, 0xc0000 ); y = IOHIDEventGetFloatValue (ptr, 0xc0001 ); z = IOHIDEventGetFloatValue (ptr, 0xc0002 ); // do whatever you need to do with the gravity ballSetAccel (x, y ); } } #define expect(x) if(!x) { printf("failed: %s/n", #x); return; } void initialize ( int hz ) { mach_port_t master; expect ( 0 == IOMasterPort (MACH_PORT_NULL, &master ) ); int page = 0xff00, usage = 3; CFNumberRef nums [ 2 ]; CFStringRef keys [ 2 ]; keys [ 0 ] = CFStringCreateWithCString ( 0, "PrimaryUsagePage", 0 ); keys [ 1 ] = CFStringCreateWithCString ( 0, "PrimaryUsage", 0 ); nums [ 0 ] = CFNumberCreate ( 0, kCFNumberSInt32Type, &page ); nums [ 1 ] = CFNumberCreate ( 0, kCFNumberSInt32Type, &usage ); CFDictionaryRef dict = CFDictionaryCreate ( 0, ( const void ** )keys, ( const void ** )nums, 2, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks ); expect (dict ); IOHIDEventSystemRef sys = (IOHIDEventSystemRef ) IOHIDEventSystemCreate ( 0 ); expect (sys ); CFArrayRef srvs = (CFArrayRef )IOHIDEventSystemCopyMatchingServices (sys, dict, 0, 0, 0 ); expect (CFArrayGetCount (srvs ) == 1 ); io_registry_entry_t serv = (io_registry_entry_t )CFArrayGetValueAtIndex (srvs, 0 ); expect (serv ); CFStringRef cs = CFStringCreateWithCString ( 0, "ReportInterval", 0 ); int rv = 1000000 /hz; CFNumberRef cn = CFNumberCreate ( 0, kCFNumberSInt32Type, &rv ); int res = IOHIDServiceSetProperty (serv, cs, cn ); expect (res == 1 ); res = IOHIDEventSystemOpen (sys, handleHIDEvent, 0, 0 ); expect (res != 0 ); }