ios 用户相册

 ## 获得自定义的所有相簿

 // 获得所有的自定义相簿
 PHFetchResult<PHAssetCollection *> *assetCollections = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
 // 遍历所有的自定义相簿
 for (PHAssetCollection *assetCollection in assetCollections) {

 }

 ## 获得相机胶卷相簿

 // 获得相机胶卷
 PHAssetCollection *cameraRoll = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeSmartAlbumUserLibrary options:nil].lastObject;

 ## 获得某个相簿的缩略图

 PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
 // 同步获得图片, 只会返回1张图片
 options.synchronous = YES;

 // 获得某个相簿中的所有PHAsset对象
 PHFetchResult<PHAsset *> *assets = [PHAsset fetchAssetsInAssetCollection:assetCollection options:nil];
 for (PHAsset *asset in assets) {
     CGSize size = CGSizeZero;

     // 从asset中获得图片
     [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:size contentMode:PHImageContentModeDefault options:options resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
         NSLog(@"%@", result);
     }];
 }

 ## 获得某个相簿的原图

 PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
 // 同步获得图片, 只会返回1张图片
 options.synchronous = YES;

 // 获得某个相簿中的所有PHAsset对象
 PHFetchResult<PHAsset *> *assets = [PHAsset fetchAssetsInAssetCollection:assetCollection options:nil];
 for (PHAsset *asset in assets) {
     CGSize size = CGSizeMake(asset.pixelWidth, asset.pixelHeight);

     // 从asset中获得图片
     [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:size contentMode:PHImageContentModeDefault options:options resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
         NSLog(@"%@", result);
     }];
 }

 ## 利用UIImagePickerController挑选图片

 // UIImagePickerController : 可以从系统自带的App(照片\相机)中获得图片

 // 判断相册是否可以打开
 if (![UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary]) return;

 UIImagePickerController *ipc = [[UIImagePickerController alloc] init];
 // 打开照片应用(显示所有相簿)
 ipc.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
 // 打开照片应用(只显示"时刻"这个相簿)
 // ipc.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
 // 照相机
 // ipc.sourceType = UIImagePickerControllerSourceTypeCamera;
 ipc.delegate = self;
 [self presentViewController:ipc animated:YES completion:nil];

 #pragma mark - <UIImagePickerControllerDelegate>
 - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
 {
     // 销毁控制器
     [picker dismissViewControllerAnimated:YES completion:nil];

     // 设置图片
     self.imageView.image = info[UIImagePickerControllerOriginalImage];
 }

 ## NaN错误
 - 错误起因:0被当做除数, 比如  / 

 ## 最简单的方法保存图片到相机胶卷

 UIImageWriteToSavedPhotosAlbum(self.imageView.image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);

 /**
  *  通过UIImageWriteToSavedPhotosAlbum函数写入图片完毕后就会调用这个方法
  *
  *  @param image       写入的图片
  *  @param error       错误信息
  *  @param contextInfo UIImageWriteToSavedPhotosAlbum函数的最后一个参数
  */
 - (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo
 {
     if (error) {
         [SVProgressHUD showErrorWithStatus:@"图片保存失败!"];
     } else {
         [SVProgressHUD showSuccessWithStatus:@"图片保存成功!"];
     }
 }

 ## 保存图片到自定义相册

 - (IBAction)save {
     /*
      PHAuthorizationStatusNotDetermined,     用户还没有做出选择
      PHAuthorizationStatusDenied,            用户拒绝当前应用访问相册(用户当初点击了"不允许")
      PHAuthorizationStatusAuthorized         用户允许当前应用访问相册(用户当初点击了"好")
      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)
      */

     // 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")
         MKLog(@"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!"];;
             }
         }];
     }];
 }

 /**
  *  获得相簿
  */
 - (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];
     });
 }

 ## Xcode插件的安装路径

 /Users/用户名/Library/Application Support/Developer/Shared/Xcode/Plug-ins