我们知道，在iPhone中获取照片库常用的方法如下：

UIImagePickerController *m_imagePicker = [[UIImagePickerController alloc] init];
    if ([UIImagePickerController isSourceTypeAvailable:
         UIImagePickerControllerSourceTypePhotoLibrary]) {
        m_imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        m_imagePicker.delegate = self;
        //        [m_imagePicker.navigationBar.subviews];
        [m_imagePicker setAllowsEditing:NO];
        //m_imagePicker.allowsImageEditing = NO;
        [self presentModalViewController:m_imagePicker animated:YES];
        [m_imagePicker release];
    }else {
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:nil message:@"Error accessing photo library!" delegate:nil cancelButtonTitle:@"Close" otherButtonTitles:nil];
        [alert show];
        [alert release];
    }

这对iPhone的操作是没有问题的。但是当我们在iPad环境中却有问题了，当我们运行时会报如下错误：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'On iPad, UIImagePickerController must be presented via UIPopoverController'

所以我们必须通过UIPopoverController来实现才行。具体实现如下：

UIImagePickerController *m_imagePicker = [[UIImagePickerController alloc] init];
    if ([UIImagePickerController isSourceTypeAvailable:
         UIImagePickerControllerSourceTypePhotoLibrary]) {
        m_imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        m_imagePicker.delegate = self;
        [m_imagePicker setAllowsEditing:NO];
        UIPopoverController *popover = [[UIPopoverController alloc] initWithContentViewController:m_imagePicker];
        self.popoverController = popover;
        //popoverController.delegate = self;
        
        [popoverController presentPopoverFromRect:CGRectMake(0, 0, 300, 300) inView:self.view permittedArrowDirections:UIPopoverArrowDirectionAny animated:YES];
        
        //[self presentModalViewController:m_imagePicker animated:YES];
        [popover release];
        [m_imagePicker release];
    }else {
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:nil message:@"Error accessing photo library!" delegate:nil cancelButtonTitle:@"Close" otherButtonTitles:nil];
        [alert show];
        [alert release];
    }
这里需要注意，对局部UIPopoverController对象popover我们赋给了一个全局的UIPopoverController对象popoverController。而不能直接调用popover。因为在popover对象还可见时，是不能够被释放的。

from:http://blog.csdn.net/fxj281314/article/details/6050588