ALAssetsgroup

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Enumerating Assets（遍历资源）

• – enumerateAssetsUsingBlock:（用一个block来遍历组里的资源）
• 用一个block来遍历组里的资源）
• 用一个block来遍历组里特定index的资源）
• 
  

Adding Assets（添加资源）

• – addAsset:（添加一个已存在的asset到接收者。返回yes成功；反之，失败。）
• property（指示程序是否可以编辑组，只读属性，打印看了一下，系统自带的是不能编辑的，其它可以编辑）
• 
  

Filtering（过滤）

• – numberOfAssets（返回组过滤器条件下的资源个数，若没有设置过滤器，则返回组里的资源个数）
• – setAssetsFilter:（设置组的过滤器）
• 
  

Accessing Properties（访问属性）

• – valueForProperty:（通过组属性名称，获取组属性：组名称，组类型，组永久性ID,组URL）
• – posterImage（组的封面）

ALAsset

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Asset Properties

• – valueForProperty:
•   (1.ALAssetPropertyType 资源的类型（照片，视频）
•    2.ALAssetPropertyLocation 资源地理位置（无位置信息返回null）
•    3.ALAssetPropertyDuation 播放时长（照片返回ALErorInvalidProperty)
•    4.ALAssetPropertyOrientation 方向（共有8个方向，参见：ALAssetOrientation)
•    5.ALAssetPropertyDate 拍摄时间（包含了年与日时分秒）
•    6.ALAssetPropertyRepresentations 描述（打印看了下，只有带后缀的名称）
•    7.ALAssetPropertyURLs（返回一个字典，键值分别是文件名和文件的url）
•    8.ALAssetPropertyAssetURL 文件的url )
• property（指示资源是否可以编辑，只读属性)
•  property（原始资源。若没有保存修改后资源，则原始资源为nil）
• 
  

Accessing Representations

• – defaultRepresentation
• – representationForUTI:
• – thumbnail（小正方形的缩略图）
• – aspectRatioThumbnail（按原始资源长宽比例的缩略图）
• 


Setting New Image and Video Data

• – setImageData:metadata:completionBlock: 
• 用给定的image data 替换接收者的image data。
• – setVideoAtPath:completionBlock: 
• 用给定的URL的video 替换接收者的video data。
  

Saving to the Saved Photos Album

• – writeModifiedImageDataToSavedPhotosAlbum:metadata:completionBlock:
• 保存image data到Saved Photos album
• – writeModifiedVideoAtPathToSavedPhotosAlbum:completionBlock: 

 保存video到Saved Photos album的指定路径

ALAssetRepresentation

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        ALAssetRepresentation对象封装了一个给定ALAsset对象的陈述。

-(void)getGroup
{
    @autoreleasepool
    {
        ALAssetsLibraryAccessFailureBlock failureblock =
        ^(NSError *myerror)
        {
            NSLog(@"相册访问失败 =%@", [myerror localizedDescription]);
            if ([myerror.localizedDescription rangeOfString:@"Global denied access"].location!=NSNotFound) {
                NSLog(@"无法访问相册.请在'设置->定位服务'设置为打开状态.");
            }else{
                NSLog(@"相册访问失败.");
            }
        };
        
        ALAssetsLibraryGroupsEnumerationResultsBlock
        libraryGroupsEnumeration = ^(ALAssetsGroup* group,BOOL* stop)
        {
            if (group!=nil)
            {
                [self.groupArray addObject:group];
            }
            else
            {
                if (!_groupTable)
                {
                    _groupTable = [[UITableView alloc] initWithFrame:EZRECT(0, 0, SCREEN_SIZE_WIDTH, SCREEN_SIZE_HEIGHT - 44)
                                                               style:UITableViewStylePlain];
                    _groupTable.delegate = self;
                    _groupTable.dataSource = self;
                    [self.view addSubview:_groupTable];
                }
                [_groupTable performSelectorOnMainThread:@selector(reloadData) withObject:nil waitUntilDone:NO];
            }
        };
        [[DataCenter defaultAssetsLibrary] enumerateGroupsWithTypes:ALAssetsGroupAll
                                                         usingBlock:libraryGroupsEnumeration
                                                       failureBlock:failureblock];
    }
}

       由于分组在添加到groupArray中，后面要在外面的函数中调用，这样会发生警告，所以，将ALAssetsLibrary的获取写成一个单例

+ (ALAssetsLibrary *)defaultAssetsLibrary
{
    static dispatch_once_t pred = 0;
    static ALAssetsLibrary *library = nil;
    dispatch_once(&pred,
                  ^{
                      library = [[ALAssetsLibrary alloc] init];
                  });
    return library;
}

     利用获得的分组再来获取资源文件：

-(void)filterImageWithGroup:(ALAssetsGroup *)group
{
    [self.images removeAllObjects];
    ALAssetsGroupEnumerationResultsBlock groupEnumerAtion =
    ^(ALAsset *result,NSUInteger index, BOOL *stop)
    {
        if (result!=NULL)
        {
            if ([[result valueForProperty:ALAssetPropertyType]isEqualToString:ALAssetTypePhoto])
            {
                [self.images addObject:result];
            }
        }
        else
        {
            //主线程中刷新UI
        }
        
    };
    [group enumerateAssetsUsingBlock:groupEnumerAtion];
}

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ALAssetsLibrary类是代表系统中整个资源库，使用它可以访问资源库中的资源和保存照片，视频等功能。

    _library = [[ALAssetsLibrary alloc]init];
    //判断当前应用是否能访问相册资源
    /*
     typedef NS_ENUM(NSInteger, ALAuthorizationStatus) {
     ALAuthorizationStatusNotDetermined = 0, 用户尚未做出了选择这个应用程序的问候
     ALAuthorizationStatusRestricted,        此应用程序没有被授权访问的照片数据。可能是家长控制权限。

     ALAuthorizationStatusDenied,            用户已经明确否认了这一照片数据的应用程序访问.
     ALAuthorizationStatusAuthorized         用户已授权应用访问照片数据.
     }
     */
    int author = [ALAssetsLibrary authorizationStatus];
    NSLog(@"author type:%d",author);
    //关闭监听共享照片流产生的频繁通知信息
    [ALAssetsLibrary disableSharedPhotoStreamsSupport];
    
    //创建一个相册到相册资源中，并通过block返回创建成功的相册ALAssetsGroup
    [_library addAssetsGroupAlbumWithName:@"test" resultBlock:^(ALAssetsGroup *group) {
        //NSString *const ALAssetsGroupPropertyName;
        //NSString *const ALAssetsGroupPropertyType;
        //NSString *const ALAssetsGroupPropertyPersistentID;
        //NSString *const ALAssetsGroupPropertyURL;
        //查看相册的名字
        NSLog(@"ALAssetsGroupPropertyName:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
        //查看相册的类型
        NSLog(@"ALAssetsGroupPropertyType:%@",[group valueForProperty:ALAssetsGroupPropertyType]);
        //查看相册的存储id
        NSLog(@"ALAssetsGroupPropertyPersistentID:%@",[group valueForProperty:ALAssetsGroupPropertyPersistentID]);
        //查看相册存储的位置地址
        NSLog(@"ALAssetsGroupPropertyURL:%@",[group valueForProperty:ALAssetsGroupPropertyURL]);
        groupURL = [group valueForProperty:ALAssetsGroupPropertyURL];

    } failureBlock:^(NSError *error) {
        
    }];

新添加了一个名为test的相册

    [NSThread sleepForTimeInterval:0.5];
    //通过url地址在相册资源中获取该地址的资源文件ALAsset，有可能是相片或视频
    [_library assetForURL:[NSURL URLWithString:@""] resultBlock:^(ALAsset *asset) {
        /*
         NSString *const ALAssetPropertyType;
         NSString *const ALAssetPropertyLocation;
         NSString *const ALAssetPropertyDuration;
         NSString *const ALAssetPropertyOrientation;
         NSString *const ALAssetPropertyDate;
         NSString *const ALAssetPropertyRepresentations;
         NSString *const ALAssetPropertyURLs;
         NSString *const ALAssetPropertyAssetURL;
         */
        //查看资源的地理位置信息
        NSLog(@"ALAssetPropertyLocation:%@",[asset valueForProperty:ALAssetPropertyLocation]);
        //如果资源是视频，查看视频的时长
        NSLog(@"ALAssetPropertyDuration:%@",[asset valueForProperty:ALAssetPropertyDuration]);
        //查看资源的方向，图片的旋转方向
        NSLog(@"ALAssetPropertyOrientation:%@",[asset valueForProperty:ALAssetPropertyOrientation]);
        //查看资源的创建时间
        NSLog(@"ALAssetPropertyDate:%@",[asset valueForProperty:ALAssetPropertyDate]);
        //查看资源的描述信息
        NSLog(@"ALAssetPropertyRepresentations:%@",[asset valueForProperty:ALAssetPropertyRepresentations]);
        NSLog(@"ALAssetPropertyURLs:%@",[asset valueForProperty:ALAssetPropertyURLs]);
        //查看资源的url路径
        NSLog(@"ALAssetPropertyAssetURL:%@",[asset valueForProperty:ALAssetPropertyAssetURL]);
    } failureBlock:^(NSError *error) {
        
    }];
    //通过url地址获取相册资源中的一个相册
    [_library groupForURL:groupURL resultBlock:^(ALAssetsGroup *group) {
        NSLog(@"ALAssetsGroupPropertyName:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
    } failureBlock:^(NSError *error) {
    
    }];
    //根据选择的类型遍历相册资源中的相对应类型的所有相册，其中stop行参是指针，表示是否停止迭代，当赋值为false则停止
    /*
     enum {
     ALAssetsGroupLibrary        = (1 << 0),
     ALAssetsGroupAlbum          = (1 << 1),
     ALAssetsGroupEvent          = (1 << 2),
     ALAssetsGroupFaces          = (1 << 3),
     ALAssetsGroupSavedPhotos    = (1 << 4),
     ALAssetsGroupPhotoStream    = (1 << 5),
     ALAssetsGroupAll            = 0xFFFFFFFF,
     };
     */
    [_library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
        NSLog(@"group name:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
    } failureBlock:^(NSError *error) {
        
    }];
    //保存图片到系统默认的相册中，使用nsdata的形式，并返回照片的url地址
    [_library writeImageDataToSavedPhotosAlbum:nil metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
        
    }];
    //保存图片到系统默认的相册中，使用cgimageref的形式，并返回照片的url地址
    [_library writeImageToSavedPhotosAlbum:nil metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
        
    }];
    
    //保存图片到系统默认的相册中，使用cgimageref的形式，并且选择图片以什么旋转方向的形式保存，并返回照片的url地址
    /*
     typedef enum {
     ALAssetOrientationUp,            // default orientation
     ALAssetOrientationDown,          // 180 deg rotation
     ALAssetOrientationLeft,          // 90 deg CCW
     ALAssetOrientationRight,         // 90 deg CW
     ALAssetOrientationUpMirrored,    // as above but image mirrored along other axis. horizontal flip
     ALAssetOrientationDownMirrored,  // horizontal flip
     ALAssetOrientationLeftMirrored,  // vertical flip
     ALAssetOrientationRightMirrored, // vertical flip
     } ALAssetOrientation;
     */
    UIImage* image = [UIImage imageNamed:@"test.png"];
    [_library writeImageToSavedPhotosAlbum:[image CGImage] orientation:ALAssetOrientationLeft completionBlock:^(NSURL *assetURL, NSError *error) {
        NSLog(@"save image:%@",assetURL);
    }];

ALAssetsGroup类是系统用于映射相册资源中的每个相册，可以通过该类获取相册中的资源文件，并且能向相册中添加资源文件

    //保存图片到系统默认的相册中，使用cgimageref的形式，并且选择图片以什么旋转方向的形式保存，并返回照片的url地址

    /*
     typedef enum {
     ALAssetOrientationUp,            // default orientation
     ALAssetOrientationDown,          // 180 deg rotation
     ALAssetOrientationLeft,          // 90 deg CCW
     ALAssetOrientationRight,         // 90 deg CW
     ALAssetOrientationUpMirrored,    // as above but image mirrored along other axis. horizontal flip
     ALAssetOrientationDownMirrored,  // horizontal flip
     ALAssetOrientationLeftMirrored,  // vertical flip
     ALAssetOrientationRightMirrored, // vertical flip
     } ALAssetOrientation;
     */
    UIImage* image = [UIImage imageNamed:@"test.png"];
    [_library writeImageToSavedPhotosAlbum:[image CGImage] orientation:ALAssetOrientationLeft completionBlock:^(NSURL *assetURL, NSError *error) {
        NSLog(@"save image:%@",assetURL);
        //通过ALAssetsLibrary迭代取出所有相册
        [_library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
            NSString* groupname = [group valueForProperty:ALAssetsGroupPropertyName];
            //如果相册的名称是test的时候，对其进行操作
            if ([groupname isEqualToString:@"test"]) {
                //设置相册组的筛选条件，ALAssetsFilter类表示筛选条件，allPhotos代表相册只包含相片，allVideos代表只包含视频，allAssets代表包含所有资源
                [group setAssetsFilter:[ALAssetsFilter allPhotos]];
                //通过刚保存的照片的url，把保存到默认相册的照片也保存到test相册中
                [_library assetForURL:assetURL resultBlock:^(ALAsset *asset) {
                    //添加资源到指定的相册
                    [group addAsset:asset];
                    //获取相册中一共的资源数量
                    int count = [group numberOfAssets];
                    NSLog(@"count:%d",count);
                    dispatch_queue_t main = dispatch_get_main_queue();
                    dispatch_async(main, ^{
                        //获取相册的封面图片
                        CGImageRef poster = [group posterImage];
                        [imageView setImage:[UIImage imageWithCGImage:poster]];
                    });
                    //NSString *const ALAssetsGroupPropertyName;
                    //NSString *const ALAssetsGroupPropertyType;
                    //NSString *const ALAssetsGroupPropertyPersistentID;
                    //NSString *const ALAssetsGroupPropertyURL;
                    //查看相册的名字
                    NSLog(@"ALAssetsGroupPropertyName:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
                    //查看相册的类型
                    NSLog(@"ALAssetsGroupPropertyType:%@",[group valueForProperty:ALAssetsGroupPropertyType]);
                    //查看相册的存储id
                    NSLog(@"ALAssetsGroupPropertyPersistentID:%@",[group valueForProperty:ALAssetsGroupPropertyPersistentID]);
                    //查看相册存储的位置地址
                    NSLog(@"ALAssetsGroupPropertyURL:%@",[group valueForProperty:ALAssetsGroupPropertyURL]);
                    //按遍历顺序获取指定索引的资源，遍历顺序可以是先序或倒序
                    /*
                     enum {
                     NSEnumerationConcurrent = (1UL << 0),
                     NSEnumerationReverse = (1UL << 1),
                     };
                     typedef NSUInteger NSEnumerationOptions;
                     */
                    [group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:0] options:NSEnumerationConcurrent usingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                        
                    }];
                    //按顺便遍历获取相册中所有的资源，index代表资源的索引，stop赋值为false时，会停止遍历
                    [group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                        
                    }];
                     //按顺便遍历获取相册中所有的资源，遍历顺序可以是先序或倒序，index代表资源的索引，stop赋值为false时，会停止遍历
                    [group enumerateAssetsWithOptions:NSEnumerationReverse usingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                        
                    }];
                    
                } failureBlock:^(NSError *error) {
                    
                }];
            }
        } failureBlock:^(NSError *error) {
            
        }];
    }];

ALAsset类代表相册中的每个资源文件，可以通过它获取资源文件的相关信息还能修改和新建资源文件，ALAssetRepresentation类代表相册中每个资源文件的详细信息，可以通过它获取资源的大小，名字，路径等详细信息。

                        //通过ALAsset获取相对应的资源，获取图片的等比缩略图，原图的等比缩略
                        CGImageRef ratioThum = [asset aspectRatioThumbnail];
                        //获取相片的缩略图，该缩略图是相册中每张照片的poster图
                        CGImageRef thum = [asset thumbnail];
                        UIImage* rti = [UIImage imageWithCGImage:ratioThum];
                        UIImage* ti = [UIImage imageWithCGImage:thum];
                        UIImageView* v1 = [[UIImageView alloc]initWithFrame:CGRectMake(20, 100, 120, 200)];
                        v1.image = rti;
                        v1.contentMode = UIViewContentModeScaleAspectFit;
                        UIImageView* v2 = [[UIImageView alloc]initWithFrame:CGRectMake(180, 100, 120, 200)];
                        v2.image = ti;
                        v2.contentMode = UIViewContentModeScaleAspectFit;
                        [self.view addSubview:v1];
                        [self.view addSubview:v2];

左侧为等比缩略图效果，右侧为poster效果的缩略图

                        UIImage* ni = [UIImage imageNamed:@"new.png"];
                        //修改指定路径的图片资源内容，替换掉原来的内容
                        [asset setImageData:UIImageJPEGRepresentation(ni, 1.0) metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
                            NSLog(@"new:%@",assetURL);
                        }];
                        //根据给定的图片内容，重新生成一张新图
                        [asset writeModifiedImageDataToSavedPhotosAlbum:UIImageJPEGRepresentation(ni, 1.0) metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
                            NSLog(@"new:%@",assetURL);
                        }];
                        //获取资源图片的详细资源信息
                        ALAssetRepresentation* representation = [asset defaultRepresentation];
                        //获取资源图片的长宽
                        CGSize dimension = [representation dimensions];
                        //获取资源图片的高清图
                        [representation fullResolutionImage];
                        //获取资源图片的全屏图
                        [representation fullScreenImage];
                        //获取资源图片的名字
                        NSString* filename = [representation filename];
                        NSLog(@"filename:%@",filename);
                        //缩放倍数
                        [representation scale];
                        //图片资源容量大小
                        [representation size];
                        //图片资源原数据
                        [representation metadata];
                        //旋转方向
                        [representation orientation];
                        //资源图片url地址，该地址和ALAsset通过ALAssetPropertyAssetURL获取的url地址是一样的
                        NSURL* url = [representation url];
                        NSLog(@"url:%@",url);
                        //资源图片uti，唯一标示符
                        NSLog(@"uti:%@",[representation UTI]);