判断是否允许使用相机

注意：此方法只对ios7以上的系统有用，刚才用“我查查”试了下，如果是在ios6的系统的话就直接崩溃了，况且ios6上也没有“设置--隐私--相机” 那一项

if(IOS7)
    {
        AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
        if (authStatus == AVAuthorizationStatusNotDetermined)
        {
            [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
                if(granted){
                    UIImagePickerController *pickerController = [[UIImagePickerController alloc] init];
                    pickerController.delegate = self;
                    pickerController.sourceType = UIImagePickerControllerSourceTypeCamera;
                    pickerController.allowsEditing = NO;
                    [self presentViewController:pickerController animated:YES completion:^{
                    }];
                }
                else
                {
                    return;
                }
            }];
        }
        else if (authStatus == AVAuthorizationStatusDenied)
        {
            UIAlertView* alert = [[UIAlertView alloc] initWithTitle: nil
                                                            message:@"请在iPhone的\"设置-隐私-相机\"选项中,允许xx访问你的相机。"
                                                           delegate:nil
                                                  cancelButtonTitle: @"确定"
                                                  otherButtonTitles:nil, nil];
            [alert show];
        }
        else if (authStatus == AVAuthorizationStatusAuthorized)
        {
            UIImagePickerController *pickerController = [[UIImagePickerController alloc] init];
            pickerController.delegate = self;
            pickerController.sourceType = UIImagePickerControllerSourceTypeCamera;
            pickerController.allowsEditing = NO;
            [self presentViewController:pickerController animated:YES completion:^{
            }];
        }
        else if (authStatus == AVAuthorizationStatusRestricted)
        {
            UIAlertView* alert = [[UIAlertView alloc] initWithTitle: nil
                                                            message:@"请在iPhone的\"设置-隐私-相机\"选项中,允许xx访问你的相机。"
                                                           delegate:nil
                                                  cancelButtonTitle: @"确定"
                                                  otherButtonTitles:nil, nil];
            [alert show];
        }
        
    }
    else
    {
        UIImagePickerController *pickerController = [[UIImagePickerController alloc] init];
        pickerController.delegate = self;
        pickerController.sourceType = UIImagePickerControllerSourceTypeCamera;
        pickerController.allowsEditing = NO;
        [self presentViewController:pickerController animated:YES completion:^{
        }];
    }