从Samples中入门IOS开发（六）------ Photo和Album浏览

MyImagePicker展示了如何调用系统Photo和Album，并在自定义的UI中进行浏览，而这个也是很大众化的需求。

先看看这个例子的使用流程：

对于这个Sample，我主要关注两个关键点：

调用系统Photo和Album
UI组件的嵌套和组合调用系统Photo和Album

IOS提供了类ALAssetsLibrary来取得Photo下面的资源（photo, album, video等），它的主要调用方式是遍历和block回调：

- (void)viewDidLoad {        self.title = @"Photo";    UIScrollView *imageScrollView = (UIScrollView *)self.view;        [imageScrollView setBackgroundColor:[UIColor blackColor]];    [imageScrollView setDelegate:self];    [imageScrollView setBouncesZoom:YES];    ALAssetRepresentation *assetRepresentation = [asset defaultRepresentation];        UIImage *fullScreenImage = [UIImage imageWithCGImage:[assetRepresentation fullScreenImage] scale:[assetRepresentation scale] orientation:(UIImageOrientation)[assetRepresentation orientation]];    // add touch-sensitive image view to the scroll view    TapDetectingImageView *imageView = [[TapDetectingImageView alloc] initWithImage:fullScreenImage];    [imageView setDelegate:self];    [imageView setTag:ZOOM_VIEW_TAG];    [imageScrollView setContentSize:[imageView frame].size];    [imageScrollView addSubview:imageView];    [imageView release];        // calculate minimum scale to perfectly fit image width, and begin at that scale    float minimumScale = [imageScrollView frame].size.width  / [imageView frame].size.width;    [imageScrollView setMinimumZoomScale:minimumScale];        [imageScrollView zoomToRect:CGRectMake(0.0, 0.0, imageView.frame.size.width, imageView.frame.size.height) animated:NO];    }

所以从这个例子中能学习到如何灵活地嵌套和组合多种UI组件，并把事件侦听delegate出来。