Three20通过三种方式加载图片

self.photoSource = [[MockPhotoSource alloc]
                        initWithType:MockPhotoSourceNormal
                        title:@"Flickr Photos"
                        pictures:[[NSArray alloc] initWithObjects:

                                  [[[MockPhoto alloc]
                                    initWithURL:@"http://farm4.static.flickr.com/3081/3164978791_3c292029f2.jpg?v=0"
                                    smallURL:@"documents://xxxx.png"
                                    size:CGSizeMake(320, 480)] autorelease]

1.@"bundle://pictures/abc/1234.jpg"
2.@"documents://xxxx.png"
3.@"http://farm4.static.flickr.com/3081/3164978791_3c292029f2.jpg?v=0"