iOS7应用开发17：摄像、Core Motion和应用实例的代理

1、关于iOS设备上的摄像头

实现在摄像头上获取图像的方法：使用UIImagePickerController。这个视图控制器不使用storyboard生成，因此需要使用alloc、init方法手动建立。显示这个ViewController的方法需要调用presentViewController::animated:completion。执行步骤：①建立视图控制器实例，并设置代理；②配置（数据源、媒体类型、是否可编辑）；③显示视图控制器；④完成获取图像后有代理的方法响应。

具体实现例子：

UIImagePickerControllerSourceType sourceType = UIImagePickerControllerSourceTypeCamera; //表示希望通过摄像头拍摄图像
if(![UIImagePickerController isSourceTypeAvailable:sourceType])//检测当前设备是否支持获取指定媒体类型的数据
{
	sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
}

UIImagePickerController *imagePickerController = [[UIImagePickerController alloc] init];//新建UIIPC实例
imagePickerController.delegate = self;   // 设置委托为当前类
imagePickerController.sourceType = sourceType;//指定媒体类型
imagePickerController.allowsEditing = YES;//设置为可以编辑
[self presentViewController:imagePickerController animated:YES completion:nil];  //需要以模态的形式展示
[imagePickerController release];

拍摄（或读取）图像完成后，还需调用delegate方法执行后续操作：

#pragma mark -
#pragma mark UIImagePickerController Method
//完成拍照
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    [picker dismissViewControllerAnimated:YES completion:^{}];
    UIImage *image = [info objectForKey:UIImagePickerControllerEditedImage];
    if (image == nil)
        image = [info objectForKey:UIImagePickerControllerOriginalImage];

    [self performSelector:@selector(saveImage:) withObject:image];

}
//用户取消拍照
-(void)imagePickerControllerDidCancel:(UIImagePickerController *)picker
{
    [picker dismissViewControllerAnimated:YES completion:nil];
}

//将照片保存到disk上
-(void)saveImage:(UIImage *)image
{

    NSData *imageData = UIImagePNGRepresentation(image);
    if(imageData == nil)
    {
        imageData = UIImageJPEGRepresentation(image, 1.0);
    }

    NSDate *date = [NSDate date];

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"yyyyMMddHHmmss"];
    _fileName = [[[formatter stringFromDate:date] stringByAppendingPathExtension:@"png"] retain];

    NSURL *saveURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:_fileName];

    [imageData writeToURL:saveURL atomically:YES];
}

2、Core Motion简介

Core Motion代表了iOS设备中的陀螺仪等模块，其提供的API可以调用设备的动作传感器，检测当前设备的动作状态。实现该功能的类为CMMotionManager，该类同样适用alloc、init创建，但是一个app中只能有一个该类的实例。该对象可认为是一个全局资源。

适用方法：①检测硬件是否支持；②启动传感器获取数据；③检测是否正在获取数据；④停止传感器；

(1)加速度

//获取三维加速度
    CMAccelerometerData *newestAccel = motionManager.accelerometerData;
    double accelerationX = newestAccel.acceleration.x;
    double accelerationY = newestAccel.acceleration.y;
    double accelerationZ = newestAccel.acceleration.z;

(2)各个方向的重力以及设备倾斜角

    double gravityX = motionManager.deviceMotion.gravity.x;
    double gravityY = motionManager.deviceMotion.gravity.y;
    double gravityZ = motionManager.deviceMotion.gravity.z;
    double zTheta = atan2(gravityZ,sqrtf(gravityX*gravityX+gravityY*gravityY))/M_PI*180.0;//与水平面的角度
    double xyTheta = atan2(gravityX,gravityY)/M_PI*180.0;//设备自身旋转的角度

(3)陀螺仪数据

角速度：

    CMRotationRate rotationRate = motionManager.deviceMotion.rotationRate;
    double rotationX = rotationRate.x;
    double rotationY = rotationRate.y;
    double rotationZ = rotationRate.z;

空间位置的欧拉角

    double roll    = motionManager.deviceMotion.attitude.roll;
    double pitch   = motionManager.deviceMotion.attitude.pitch;
    double yaw     = motionManager.deviceMotion.attitude.yaw;

空间位置的四元数

   double w = motionManager.deviceMotion.attitude.quaternion.w;
   double wx = motionManager.deviceMotion.attitude.quaternion.x;
   double wy = motionManager.deviceMotion.attitude.quaternion.y;
   double wz = motionManager.deviceMotion.attitude.quaternion.z;

3、应用的状态

当应用UI开始/停止接收消息时，应用的代理会分别调用以下方法：

- (void)applicationDidBecomeActive:(UIApplication *)sender;
- (void)applicationWillResignActive:(UIApplication *)sender;

同时将会发送两条广播消息：UIApplicationDidBecomeActiveNotification和UIApplicationWillResignActiveNotification。可以使用这两个消息用于暂停和重启应用。

当应用进入后台时/从后台重启时，会调用：

- (void)applicationDidEnterBackground:(UIApplication *)sender;
- (void)applicationWillEnterForgound:(UIApplication *)sender;

并发送UIApplicationDidEnterBackgroundNotification和UIApplicationWillEnterForgroundNotification。
除此之外还有其他代理方法，如本地消息、UI恢复状态、数据保护、打开URL等。