PHPhotoLibrary的简单使用--保存图片、视频到相册

不知道你们有没有这样的侥幸心理：Apple更新了新的框架API，旧的虽然被标为废弃了但还是能用，就一直用着旧的偷懒不去改最新的。有句话说得好：不是不报，时候未到。我最近遇到了要报的懒。

在iOS里，保存图片到相册有一个简单的UIImage的方法：
UIImageWriteToSavedPhotosAlbum(_image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);
然后需要实现上面SEL里的回调，一个系统的方法：

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo {
      if (error) {
          NSLog(@"保存失败");
      } else {
          NSLog(@"保存成功");
      }
  }

当然这个只能简单的保存图片到默认的系统相册中，如果要创建自己的相册，就需要用ALAssetsLibrary框架：

// 先保存图片
- (void)saveImage:(UIImage*)image toAlbum:(NSString *)albumName{  
    ALAssetsLibrary *assetsLibrary = [[ALAssetsLibrary alloc]init];  
    [assetsLibrary writeImageToSavedPhotosAlbum:[image CGImage] orientation:(ALAssetOrientation)image.imageOrientation completionBlock:^(NSURL *assetURL, NSError *error) {  
        if (error) {  
            NSLog(@"Save image fail：%@",error);  
        }else{  
            NSLog(@"Save image succeed."); 
            [self addAssetURL:assetURL toAlbum:albumName withAssestLibrary:assetsLibrary completionBlock:(SaveRecordCompletion)completionBlock failBlock:(void(^)(NSError *error))failBlock] ;
        }  
    }];  

// 再添加到指定相册
-(void)addAssetURL:(NSURL*)assetURL toAlbum:(NSString*)albumName withAssestLibrary:(ALAssetsLibrary *)assetsLibrary completionBlock:(SaveRecordCompletion)completionBlock failBlock:(void(^)(NSError *error))failBlock
{
    __block BOOL albumWasFound = NO;
    
    //遍历所有的相册
    [assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAlbum usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
        //compare the names of the albums
        if ([albumName compare: [group valueForProperty:ALAssetsGroupPropertyName]] == NSOrderedSame)
        {
            //找到名字为albumName的相册
            albumWasFound = YES;
            
            //get a hold of the photo's asset instance
            [assetsLibrary assetForURL: assetURL resultBlock:^(ALAsset *asset) {
                //add photo to the target album
                //NSAssert(asset != nil, @"asset不能为空");
                [group addAsset: asset];
            } failureBlock: nil];
            *stop = YES;
        }
        
        if (group==nil && albumWasFound==NO)
        {
            __weak ALAssetsLibrary* weakAssetsLibrary = assetsLibrary;
            
            [self addAssetsGroupAlbumWithName:albumName resultBlock:^(ALAssetsGroup *group) {
                
                [weakAssetsLibrary assetForURL: assetURL resultBlock:^(ALAsset *asset)
                 {
                     NSAssert(asset != nil, @"asset不能为空");
                     //add photo to the newly created album
                     [group addAsset: asset];

                 } failureBlock: nil];
                
            } failureBlock: nil];
            *stop = YES;
        }
    } failureBlock:failBlock];
}

因为ALAssetsLibrary的API在iOS9之后被标位弃用了，所以会有出错的风险。我遇到的问题是，当开启使用iCloud图库时，图片只会保存在系统默认的相册下，保存不到我们应用的相册下，关闭iCloud时就不会有这种问题（在iOS10、11下出现的）。所以怀疑到应该是在开启iCloud时，苹果做了一些操作导致旧的框架不支持了。

下面主要看下在iOS8后出现的Photos框架的简单使用。

首先，我们可以创建一个helpe类，用来单独做对相册的操作（比如我的叫SRHPhotoHelper，当然你可以按照自己的想法随意写）。
直接上代码：

+ (void)srh_saveImage:(UIImage *)image completionHandle:(void (^)(NSError *, NSString *))completionHandler {
    // 1. 获取照片库对象
    PHPhotoLibrary *library = [PHPhotoLibrary sharedPhotoLibrary];
    
    // 假如外面需要这个 localIdentifier ，可以通过block传出去
    __block NSString *localIdentifier = @"";
    
    // 2. 调用changeblock
    [library performChanges:^{
        
        // 2.1 创建一个相册变动请求
        PHAssetCollectionChangeRequest *collectionRequest = [self getCurrentPhotoCollectionWithAlbumName:SRHAlbumName];
        
        // 2.2 根据传入的照片，创建照片变动请求
        PHAssetChangeRequest *assetRequest = [PHAssetChangeRequest creationRequestForAssetFromImage:image];
        
        // 2.3 创建一个占位对象
        PHObjectPlaceholder *placeholder = [assetRequest placeholderForCreatedAsset];
        localIdentifier = placeholder.localIdentifier;
        
        // 2.4 将占位对象添加到相册请求中
        [collectionRequest addAssets:@[placeholder]];
        
    } completionHandler:^(BOOL success, NSError * _Nullable error) {
        
        if (error) {
            [iConsole log:@"保存照片出错>>>%@", [error description]];
            completionHandler(error, nil);
        } else {
            completionHandler(nil, localIdentifier);
        }
    }];
}

+ (PHAssetCollectionChangeRequest *)getCurrentPhotoCollectionWithAlbumName:(NSString *)albumName {
    // 1. 创建搜索集合
    PHFetchResult *result = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    
    // 2. 遍历搜索集合并取出对应的相册，返回当前的相册changeRequest
    for (PHAssetCollection *assetCollection in result) {
        if ([assetCollection.localizedTitle containsString:albumName]) {
            PHAssetCollectionChangeRequest *collectionRuquest = [PHAssetCollectionChangeRequest changeRequestForAssetCollection:assetCollection];
            return collectionRuquest;
        }
    }
    
    // 3. 如果不存在，创建一个名字为albumName的相册changeRequest
    PHAssetCollectionChangeRequest *collectionRequest = [PHAssetCollectionChangeRequest creationRequestForAssetCollectionWithTitle:albumName];
    return collectionRequest;
}

具体的讲解可以自己去查API或者看一下这篇文章、这篇文章。后续我会把取相册图片、视频的代码分享出来，包括完整的demo。