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最近要做穿戴式裝置的App，需要研究Apple Watch如何使用加速度計 (Using Accelerometer)。

首先研究Apple的文件Core Motion Framework。

它這麼介紹：

Core Motion reports motion- and environment-related data from the onboard hardware of iOS devices, including from the accelerometers, gyroscopes, pedometers, magnetometers, and barometers. You use this framework to access hardware-generated data so that you can use it in your app. For example, a game might use accelerometer and gyroscope data to control onscreen game behavior.

Many services of this framework let you access both the raw values recorded by the hardware and a processed version of those values. Processed values do not include forms of bias that might adversely affect how you use that data. For example, a processed accelerometer value reflects only the acceleration caused by the user and not the acceleration caused by gravity.

接著隨意創立一個專案，並加入Watch App的Target。一共需要3個ID，可參考先前文章：Watch App三個ID設定。

接著直接在InterfaceController.m寫code，並連結畫面3個Label：

/**
 Theme: Watch Accelerometer
 IDE: Xcode 9
 Language: Objective C
 Date: 107/02/06
 Author: HappyMan
 Blog: https://cg2010studio.com/
 */

//
//  InterfaceController.m
//  Watch Extension
//
//  Created by HappyBoy on 02/02/2018.
//  Copyright © 2018 Jason. All rights reserved.
//

#import "InterfaceController.h"
#import <CoreMotion/CoreMotion.h>
#import <WatchConnectivity/WatchConnectivity.h>
#import <HealthKit/HealthKit.h>

@interface InterfaceController() <WCSessionDelegate, HKWorkoutSessionDelegate>

@property (unsafe_unretained, nonatomic) IBOutlet WKInterfaceLabel *xLabel;
@property (unsafe_unretained, nonatomic) IBOutlet WKInterfaceLabel *yLabel;
@property (unsafe_unretained, nonatomic) IBOutlet WKInterfaceLabel *zLabel;

@property (nonatomic, strong) CMMotionManager *manager;
@property (nonatomic, strong) HKHealthStore *healthStore;
@end

@implementation InterfaceController

- (void)awakeWithContext:(id)context {
    [super awakeWithContext:context];

    HKWorkoutSession *session = [[HKWorkoutSession alloc] initWithActivityType:HKWorkoutActivityTypeRunning  locationType:HKWorkoutSessionLocationTypeOutdoor];
    session.delegate = self;
    [self.healthStore startWorkoutSession:session];

    CMMotionManager *motionMgr = [[CMMotionManager alloc] init];
    if([motionMgr isAccelerometerAvailable])
        NSLog(@"Apple Watch: Accelerometer is available");
    if([motionMgr isGyroAvailable])
        NSLog(@"Apple Watch: Gyroscope is available");
    if([motionMgr isMagnetometerAvailable])
        NSLog(@"Apple Watch: Magnetometer is available");
    if([motionMgr isDeviceMotionAvailable])
        NSLog(@"Apple Watch: Device motion identification is available");
}

- (void)willActivate {
    // This method is called when watch view controller is about to be visible to user
    [super willActivate];

    WCSession* session = [WCSession defaultSession];
    session.delegate = self;
    [session activateSession];

    _manager = [[CMMotionManager alloc] init];
    if (_manager.accelerometerAvailable) {
        NSLog(@"accelerometer Available");
        _manager.accelerometerUpdateInterval = 0.1;
        [_manager startAccelerometerUpdatesToQueue:[[NSOperationQueue alloc] init] withHandler:^(CMAccelerometerData * _Nullable accelerometerData, NSError * _Nullable error) {
            CMAcceleration acc = accelerometerData.acceleration;
            //NSLog(@"%f,%f,%f",acc.x,acc.y,acc.x);
            NSString* x = [NSString stringWithFormat:@"x:%lf",acc.x];
            NSString* y = [NSString stringWithFormat:@"y:%lf",acc.y];
            NSString* z = [NSString stringWithFormat:@"z:%lf",acc.z];

            dispatch_async(dispatch_get_main_queue(), ^{

                [self.xLabel setText:x];
                [self.yLabel setText:y];
                [self.zLabel setText:z];
            });
        }];
    }
}

- (void)didDeactivate {
    // This method is called when watch view controller is no longer visible
    [super didDeactivate];
}

- (void)session:(WCSession *)session didReceiveMessage:(NSDictionary<NSString *,id> *)message {

}

- (void)workoutSession:(HKWorkoutSession *)workoutSession didFailWithError:(NSError *)error {

}

我們知道iPhone的感應器有4個都能使用：

• Accelerometer
• Gyroscope
• Magnetometer
• Device motion

然而Watch目前只開放2個：

• Accelerometer
• Device motion

期待未來Apple大發慈悲心，讓我開發者可以盡情發揮Watch的潛力！像是watchOS 4開放存取即時心率，藍芽功能也開放更多功能的權限！

有空在Watch上寫支遊戲App，就使用感應器來操作，想必一定很有趣：Ｄ～

參考：A Guide to Develop a Fall Detection Application in Apple Watch、iOS/WatchOS 加速度數據獲取、Core Motion Framework。