UIImagePickerController

UIImagePickerController:
1. 有三种工作模式：

//打开图片库根目录选择
UIImagePickerControllerSourceTypePhotoLibrary
//使用相机选择
UIImagePickerControllerSourceTypeCamera
//打开SavedPhoto目录选择
UIImagePickerControllerSourceTypeSavedPhotosAlbum

2. //用此方法可以判断，设备是否有拍照功能。
if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
       
        //用模式窗体转换到图片选取界面。
        UIImagePickerController *aImagePickerController = [[UIImagePickerController alloc] init];
        aImagePickerController.delegate = self;
        aImagePickerController.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        BarStreetAppDelegate *delegate = [[UIApplication sharedApplication] delegate];
        [delegate.navController presentModalViewController:aImagePickerController animated:YES];
        [aImagePickerController release];
}

3. //两个主要的委托方法
#pragma mark UIImagePickerController Delegate Methods
//返回选取的图片
- (void)imagePickerController:(UIImagePickerController *)picker
        didFinishPickingImage:(UIImage *)image
                  editingInfo:(NSDictionary *)editingInfo {
    aImageView.image=image;
    [picker dismissModalViewControllerAnimated:YES];  
}
//选取结束时调用
- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {
    [picker dismissModalViewControllerAnimated:YES]; 
}

4. iPhone Simulator获取获取图片方法。
  a. 使用safari，按住图片，选择保存；
  b.（来自http://stackoverflow.com/questions/468879/adding-images-to-iphone-simulator）Go to ~/Library/Application Support/iPhone Simulator/User/Media/DCIM/100APPLE/ and add IMG_nnnn.THM and IMG_nnnn.JPG. It doesn't matter if they are not JPEGs - they can both be PNGs, but it appears that both of them must be present for it to work. You may need to create DCIM if it doesn't already exist, and in that case you should start nnnn from 0001. The JPG files are the fullsize version, while the THM files are the thumbnail, and are 75x75 pixels in size. I wrote a script to do this, but there's a better documented one over here.
You can also add photos from safari in the simulator, by Tapping and Holding on the image. If you drag an image (or any other file, like a PDF) to the simulator, it will immediately open Safari and display the image, so this is quite an easy way of getting images to it.