在iOS中，我们调用摄像头和选择相册中的资源，我们可以使用：UIImagePickerController类来完成。

当然，我们也可以不使用UI的形式来访问iOS设备的相册资源。

那就是使用：ALAssetsLibrary

一、ALAssetsLibrary是什么

可以说，是一个桥梁把。连接了我们应用程序和相册之间的访问。

ALAssetsLibrary提供了我们对iOS设备中的相片、视频的访问。

ALAssetsLibrary被封装在 框架中。所以，我们在使用时，需要引入该框架。

贴：

self.view.backgroundColor = [UIColor whiteColor];

    self.assetsLibrary = [[ALAssetsLibrary alloc] init];

    dispatch_queue_t dispatchQueue =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_async(dispatchQueue, ^(void) {

        // 遍历所有相册

        [self.assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAll

                                          usingBlock:^(ALAssetsGroup *group, BOOL*stop) {

                                              // 遍历每个相册中的项ALAsset

                                              [group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index,BOOL *stop) {

                                                  

                                                  __block BOOL foundThePhoto =NO;

                                                  if (foundThePhoto){

                                                      *stop = YES;

                                                  }

                                                  // ALAsset的类型

                                                  NSString *assetType = [resultvalueForProperty:ALAssetPropertyType];

                                                  if ([assetTypeisEqualToString:ALAssetTypePhoto]){

                                                      foundThePhoto = YES;

                                                      *stop = YES;

                                                      ALAssetRepresentation*assetRepresentation =[result defaultRepresentation];

                                                      CGFloat imageScale = [assetRepresentation scale];

                                                      UIImageOrientationimageOrientation = (UIImageOrientation)[assetRepresentation orientation];

                                                     dispatch_async(dispatch_get_main_queue(), ^(void) {

                                                          CGImageRefimageReference = [assetRepresentation fullResolutionImage];

                                                          // 对找到的图片进行操作

                                                          UIImage *image =[[UIImage alloc] initWithCGImage:imageReference scale:imageScaleorientation:imageOrientation];

                                                          if (image != nil){

                                                              self.imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];

                                                             self.imageView.contentMode = UIViewContentModeScaleAspectFit;

                                                             self.imageView.image = image;

                                                              [self.viewaddSubview:self.imageView];

                                                          } else {

                                                              NSLog(@"Failed to create the image.");

                                                          } });

                                                  }

                                              }];

                                          }

                                          failureBlock:^(NSError *error) {

                                              NSLog(@"Failed to enumerate the asset groups.");

                                          }];

        

    });

乱啊，没办法，在xCode中是OK的。

需要解释的几点：

1.流程：该代码的流程，就是先遍历所有相册，然后，遍历每个相册中的第一张图片。

2.ALAssetsGroup：指代一个相册。

3.ALAsset：每一个ALAsset代表一个单一资源文件（也就是一张图片，或者一个视频文件）

4.ALAssetRepresentation：ALAssetRepresentation封装了ALAsset，包含了一个资源文件中的很多属性。（可以说是ALAsset的不同的表示方式，本质上都表示同一个资源文件）