1.保存图片---判断当前状态(用户是否允许访问相册)

- (IBAction)save:(UIButton *)sender {
    
    // 判断授权状态
    PHAuthorizationStatus status = [PHPhotoLibrary authorizationStatus];
    if (status == PHAuthorizationStatusRestricted) { // 因为家长控制, 导致应用无法方法相册(跟用户的选择没有关系)
        [SVProgressHUD showErrorWithStatus:@"因为系统原因, 无法访问相册"];
    } else if (status == PHAuthorizationStatusDenied) { // 用户拒绝当前应用访问相册(用户当初点击了"不允许")
       NSLog(@"提醒用户去[设置-隐私-照片-xxx]打开访问开关");
    } else if (status == PHAuthorizationStatusAuthorized) { // 用户允许当前应用访问相册(用户当初点击了"好")
        [self saveImage];
    } else if (status == PHAuthorizationStatusNotDetermined) { // 用户还没有做出选择
        // 弹框请求用户授权
        [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
            if (status == PHAuthorizationStatusAuthorized) { // 用户点击了好
                [self saveImage];
            }
        }];
    }
}

(void)saveImage
{
    // PHAsset : 一个资源, 比如一张图片\一段视频
    // PHAssetCollection : 一个相簿
    
    // PHAsset的标识, 利用这个标识可以找到对应的PHAsset对象(图片对象)
    __block NSString *assetLocalIdentifier = nil;
    
    // 如果想对"相册"进行修改(增删改), 那么修改代码必须放在[PHPhotoLibrary sharedPhotoLibrary]的performChanges方法的block中
    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
        // 1.保存图片A到"相机胶卷"中
        // 创建图片的请求
        assetLocalIdentifier = [PHAssetCreationRequest creationRequestForAssetFromImage:self.imageView.image].placeholderForCreatedAsset.localIdentifier;
    } completionHandler:^(BOOL success, NSError * _Nullable error) {
        if (success == NO) {
            [self showError:@"保存图片失败!"];
            return;
        }

2.获得相簿

        PHAssetCollection *createdAssetCollection = [self createdAssetCollection];
        if (createdAssetCollection == nil) {
            [self showError:@"创建相簿失败!"];
            return;
        }
        
        [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
            // 3.添加"相机胶卷"中的图片A到"相簿"D中
            
            // 获得图片
            PHAsset *asset = [PHAsset fetchAssetsWithLocalIdentifiers:@[assetLocalIdentifier] options:nil].lastObject;
            
            // 添加图片到相簿中的请求
            PHAssetCollectionChangeRequest *request = [PHAssetCollectionChangeRequest changeRequestForAssetCollection:createdAssetCollection];
            
            // 添加图片到相簿
            [request addAssets:@[asset]];
        } completionHandler:^(BOOL success, NSError * _Nullable error) {
            if (success == NO) {
                [self showError:@"保存图片失败!"];;
            } else {
                [self showSuccess:@"保存图片成功!"];;
            }
        }];
    }];
}

 -(PHAssetCollection *)createdAssetCollection
{
    // 从已存在相簿中查找这个应用对应的相簿
    PHFetchResult<PHAssetCollection *> *assetCollections = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    for (PHAssetCollection *assetCollection in assetCollections) {
        if ([assetCollection.localizedTitle isEqualToString:XMGAssetCollectionTitle]) {
            return assetCollection;
        }
    }
    
    // 没有找到对应的相簿, 得创建新的相簿
    
    // 错误信息
    NSError *error = nil;
    
    // PHAssetCollection的标识, 利用这个标识可以找到对应的PHAssetCollection对象(相簿对象)
    __block NSString *assetCollectionLocalIdentifier = nil;
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        // 创建相簿的请求
        assetCollectionLocalIdentifier = [PHAssetCollectionChangeRequest creationRequestForAssetCollectionWithTitle:XMGAssetCollectionTitle].placeholderForCreatedAssetCollection.localIdentifier;
    } error:&error];
    
    // 如果有错误信息
    if (error) return nil;
    
    // 获得刚才创建的相簿
    return [PHAssetCollection fetchAssetCollectionsWithLocalIdentifiers:@[assetCollectionLocalIdentifier] options:nil].lastObject;
}

  - (void)showSuccess:(NSString *)text
{
    dispatch_async(dispatch_get_main_queue(), ^{
        [SVProgressHUD showSuccessWithStatus:text];
    });
}

 - (void)showError:(NSString *)text
{
    dispatch_async(dispatch_get_main_queue(), ^{
        [SVProgressHUD showErrorWithStatus:text];
    });
}