使用AssetsLibrary.Framework创建多图片选择控制器(翻译)
系统的UIImagePickerController只能让用户选择单图片，而一般情况下，我们需要上传多张图片，这时应该可以同时选择多张图片，否则用户体验会很差。因此多图片选择器就诞生了。
在类库中，苹果为我们提供了一个AssetsLibrary.Framework的库，可以通过它获取设备里的图片和视频。在使用这个类库时， 我们需要导入，且<AssetsLibrary/AssetsLibrary.h>。然后我们可以使用它来获取不同组的枚举。
1 void (^assetGroupEnumerator)
2 (struct ALAssetsGroup *, BOOL *) = ^(ALAssetsGroup *group, BOOL *stop{
3 if(group != nil) {
4 [assetGroups addObject:group];
5 NSLog(@"Number of assets in group: %d",
6 [group numberOfAssets]);
7 }
8 };
9
10 assetGroups = [[NSMutableArray alloc] init];
11 ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
12 NSUInteger groupTypes = ALAssetsGroupAll;
13
14 [library enumerateGroupsWithTypes:groupTypes
15 usingBlock:assetGroupEnumerator
16 failureBlock:^(NSError *error) {NSLog(@"A problem occurred");}];
17
18 NSLog(@"Asset groups: %@", assetGroups);
19 [library release];
1-8行，我们声明一个block，使用它来枚举所有asset group,然后将所有获取到的group放在NSMutableArray中。
1 void (^assetEnumerator)
2 (struct ALAsset *, NSUInteger, BOOL *) = ^(ALAsset *result, NSUInteger index, BOOL *stop) {
3 if(result != nil) {
4 if(![assetURLDictionaries containsObject:[result valueForProperty:ALAssetPropertyURLs]]) {
5 if(![[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypeVideo]) {
6 [assetURLDictionaries addObject:[result valueForProperty:ALAssetPropertyURLs]];
7 [assets addObject:result];
8 }
9 }
10 }
11 };
12
13 assets = [[NSMutableArray alloc] init];
14 assetURLDictionaries = [[NSMutableArray alloc] init];
15
16 NSInteger indexOfExampleGallery = NSNotFound;
17 for (ALAssetsGroup *group in assetGroups) {
18 if ([[group valueForProperty:ALAssetsGroupPropertyName]
19 isEqualToString:@"ExampleGallery"])
20 indexOfExampleGallery = [assetGroups indexOfObject:group];
21 }
22
23 if (indexOfExampleGallery != NSNotFound) {
24 [[assetGroups objectAtIndex:indexOfExampleGallery]
25 enumerateAssetsUsingBlock:assetEnumerator];
26 NSLog(@"Assets %@", assets);
27 }
28 else
29 NSLog(@"Gallery 'ExampleGallery' not found on device.");
代码中的ELCImagePickerController就是使用这个库来完成同时选择多张图片，当然视频也可以。
ELCImagePickerController的使用
1 ELCAlbumPickerController *albumController = [[ELCAlbumPickerController alloc] initWithNibName:@"ELCAlbumPickerController" bundle:[NSBundle mainBundle]];
2 ELCImagePickerController *elcPicker = [[ELCImagePickerController alloc] initWithRootViewController:albumController];
3 [albumController setParent:elcPicker];
4 [elcPicker setDelegate:self];
5
6 ELCImagePickerDemoAppDelegate *app = (ELCImagePickerDemoAppDelegate *)[[UIApplication sharedApplication] delegate];
7 [app.viewController presentModalViewController:elcPicker animated:YES];
