/* 一般扫描二维码的代码 (iOS7之后的)*/
 
// 创建AVCaptureSession
AVCaptureSession *captureSession = [[AVCaptureSession alloc] init];
self.session = captureSession;
// 配置输入设备
AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *inputDevice = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:nil];

[captureSession addInput:inputDevice];

// 配置输出模式
AVCaptureMetadataOutput *captureOutput = [[AVCaptureMetadataOutput alloc] init];
[captureOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[captureSession addOutput:captureOutput];
[captureOutput setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];

// 添加显示内容的layer
self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:captureSession];
self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
self.previewLayer.frame = self.view.bounds;
[self.view.layer addSublayer:self.previewLayer];

/* 该部分代码整理自互联网 */

AVCaptureConnection *previewLayerConnection = self.previewLayer.connection;

// 获得当前屏幕方向
    UIInterfaceOrientation interfaceOrientation = [UIApplication sharedApplication].statusBarOrientation;
// 判断是否允许设置
    if ([previewLayerConnection isVideoOrientationSupported]) {
        // 根据当前屏幕方向来设置摄像头方向
        switch (interfaceOrientation) {
            case UIInterfaceOrientationPortrait:
                [previewLayerConnection setVideoOrientation:AVCaptureVideoOrientationPortrait];
                //竖屏，Home键在底部
                break;
            case UIInterfaceOrientationLandscapeRight:
                [previewLayerConnection setVideoOrientation:AVCaptureVideoOrientationLandscapeRight]; 
                //横屏，Home键在右边 
                break;
            case UIInterfaceOrientationLandscapeLeft:
                [previewLayerConnection setVideoOrientation:AVCaptureVideoOrientationLandscapeLeft]; 
                //横屏，Home键在左边 
                break;
            default:
                [previewLayerConnection setVideoOrientation:AVCaptureVideoOrientationPortrait]; 
                //其他方向都设置成竖屏
                break;
        }
    }

/*
Student 类声明了一个name属性和一个对象方法study
*/
Student * student = [[Student alloc] init];
student.name = @"Jack"; // 这句相当于[student setName:@"Jack"];
NSString * studentName = student.name; // 这句相当于 NSString * studentName = [student name];
student.study; // 相当于 [student study];

// 这是一个错误写法，会产生死循环
- (void)setName:(NSString *)name {
    self.name = name; // 相当于[self setName:name];
    // 所以就会一直递归调用setName:方法，导致死循环了
}

// 这也是一个错误写法，原因也是一样，会一直递归调用name方法，导致死循环
- (NSString *)name {
    return self.name; // 相当于return [self name];
}