如何检查iPad当前版本的相机操作？

if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])
{
    UIImagePickerController *picker = [[UIImagePickerController alloc] init];
    picker.sourceType = sourceType;
    picker.delegate = self;
    if(sourceType == UIImagePickerControllerSourceTypeCamera)
        [picker takePicture];
    [self presentModalViewController:picker animated:YES];
    [picker release];
}

picker.cameraDevice = UIImagePickerControllerCameraDeviceFront;

picker.cameraDevice = UIImagePickerControllerCameraDeviceRear;