媒体层图形技术之AssetsLibrary 学习笔记

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1.ALAsset

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

Asset Properties

Accessing Representations

Setting New Image and Video Data

Saving to the Saved Photos Album

保存video到Saved Photos album的指定路径

//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];

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);                        }];

2.ALAssetRepresentation

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。

ALAssetRepresentation

---------------------------------------------------------------------------

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

一个在资源库中给定的asset可能有不止一个陈述。比如，如果一个相机提供RAW和JPEG格式的图像版本，

asset将有两个陈述版本，一个是RAW的,一个是JPEG的。

Getting Image Representations

`– CGImageWithOptions:`
`– fullResolutionImage（完全分辨率的图片）`
`– fullScreenImage（满屏的图片）`

Getting Image Attributes

`– orientation（文件方向）`
`– scale（长宽比例）`
`– filename（文件名字）`

Getting Raw Data

`– size（文件尺寸，以byte为单位）`
`– getBytes:fromOffset:length:error:`

Getting Metadata

– UTI

– metadata

Getting an URL
– url

 //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]);

3.ALAssetsFilter

过滤器筛选出想要展现的资源：图片资源、视频资源

// Get all photos assets in the assets group.+ (ALAssetsFilter *)allPhotos;// Get all video assets in the assets group.+ (ALAssetsFilter *)allVideos;// Get all assets in the group.+ (ALAssetsFilter *)allAssets;

4.ALAssetsGroup

Enumerating Assets（遍历资源）

- (void)setupAssets{    self.title = [self.assetsGroup valueForProperty:ALAssetsGroupPropertyName];        if (!self.assets)        self.assets = [[NSMutableArray alloc] init];    else        [self.assets removeAllObjects];        ALAssetsGroupEnumerationResultsBlock resultsBlock = ^(ALAsset *asset, NSUInteger index, BOOL *stop) {        if (asset)        {            [self.assets addObject:asset];                        NSString *type = [asset valueForProperty:ALAssetPropertyType];                        if ([type isEqual:ALAssetTypePhoto])                self.numberOfPhotos ++;            if ([type isEqual:ALAssetTypeVideo])                self.numberOfVideos ++;        }                else if (self.assets.count > 0)        {            [self.collectionView reloadData];            [self.collectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForItem:self.assets.count-1 inSection:0]                                        atScrollPosition:UICollectionViewScrollPositionTop                                                animated:YES];        }    };        [self.assetsGroup enumerateAssetsUsingBlock:resultsBlock];}

Adding Assets（添加资源）

Filtering（过滤）

Accessing Properties（访问属性）

5.ALAssetsLibrary

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。

 //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

    //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) {

    }];

利用资源库得枚举函数把资源组分类，代码如下：

- (void)setupGroup{    if (!self.assetsLibrary)        self.assetsLibrary = [self.class defaultAssetsLibrary];        if (!self.groups)        self.groups = [[NSMutableArray alloc] init];    else        [self.groups removeAllObjects];        CTAssetsPickerController *picker = (CTAssetsPickerController *)self.navigationController;    ALAssetsFilter *assetsFilter = picker.assetsFilter;        ALAssetsLibraryGroupsEnumerationResultsBlock resultsBlock = ^(ALAssetsGroup *group, BOOL *stop) {                if (group)        {            [group setAssetsFilter:assetsFilter];                        if (group.numberOfAssets > 0)                [self.groups addObject:group];                    }        else        {            [self reloadData];        }    };            ALAssetsLibraryAccessFailureBlock failureBlock = ^(NSError *error) {                [self showNotAllowed];    };        // Enumerate Camera roll first    [self.assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos                                      usingBlock:resultsBlock                                    failureBlock:failureBlock];    // Then all other groups    NSUInteger type =    ALAssetsGroupLibrary | ALAssetsGroupAlbum | ALAssetsGroupEvent |    ALAssetsGroupFaces | ALAssetsGroupPhotoStream;        [self.assetsLibrary enumerateGroupsWithTypes:type                                      usingBlock:resultsBlock                                    failureBlock:failureBlock];}

其中得[self.classdefaultAssetsLibrary]为单列形式：

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

    //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);
    }];

详情请参考demon：http://download.csdn.net/detail/choudang/7446365

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