IOS programming 4th Edition

11.camera
Gold Challenge
问题：利用UIImagePickerController 中cameraOverlayView属性。使其在取景视图的正中显示一个十字。
代码如下：
//添加照片

• (IBAction)takePicture:(id)sender {
  UIImagePickerController *imagePicker =
  [[UIImagePickerController alloc] init];

  //如果设备支持相机，就使用拍照模式
  //否则让用户从照片库中选择照片
  if ([UIImagePickerController
  isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
  imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
  imagePicker.showsCameraControls = YES;
  //相机十字显示
  UIView *crosshair = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 60, 60)];
  crosshair.backgroundColor = [UIColor clearColor];
  //横线
  UIView *line1=[[UIView alloc]initWithFrame:CGRectMake(0, 29.5, 60, 1)];
  line1.backgroundColor=[UIColor whiteColor];
  [crosshair addSubview:line1];
  //竖线
  UIView *line2=[[UIView alloc]initWithFrame:CGRectMake(29.5, 0, 1, 60)];
  line2.backgroundColor=[UIColor whiteColor];
  [crosshair addSubview:line2];

    crosshair.center = self.view.center;
    imagePicker.cameraOverlayView = crosshair;
  

  }else{
  imagePicker.sourceType =
  UIImagePickerControllerSourceTypePhotoLibrary;

  }
  //可编辑
  imagePicker.allowsEditing = YES;

  imagePicker.delegate = self;

  //以模态的形式显示UIImagePickerController对象
  [self presentViewController:imagePicker animated:YES completion:nil];
  }