如何比较PHAsset和UIImage

Question

我已将一些转换PHAsset为UIImage:

 PHImageManager *manager = [PHImageManager defaultManager];
            [manager requestImageForAsset:asset
                               targetSize:PHImageManagerMaximumSize
                              contentMode:PHImageContentModeDefault
                                  options:requestOptions
                            resultHandler:^void(UIImage *image, NSDictionary *info) {
                                convertedImage = image;
                                [images addObject:convertedImage];
                            }];

现在我想做那样的事情:

[selectedAssets removeObject:image];

其中selectedAssets是的阵列PHAsset和image是UIImage

所以我已经实现了isEqual:

- (BOOL)isEqual:(id)other {
    if (other == self)
        return YES;
    if (!other || ![[other class] isEqual:[self class]])
        return NO;

    NSData *data1 = UIImagePNGRepresentation(self.image);
    NSData *data2 = UIImagePNGRepresentation(((TINSelectedImage*)other).image);

    return   [data1 isEqual:data2];
}

但它不起作用!

Answer 1

您不应该比较图像,而应该比较PHAssets或它们唯一有用的部分名为localIdentifier.

您正在寻找区分资产的东西称为PHAsset的localIdentifier属性.

Apple Docs将其定义为:

A unique string that persistently identifies the object. (read-only)

对不起,这个答案有点宽泛,因为我不喜欢你的方法.

如果我是你,我会这样做:

首先创建一个自定义类,我们将其命名为PhotoInfo.(如果您不想保留有关照片的大量信息,则不必执行此操作.如果是这种情况,请根据需要直接使用PHAssets的PFFetchResults.但我会使用CustomClass).

在PhotoInfo.h中:

#import <Foundation/Foundation.h>
@interface PhotoInfo : NSObject

@property NSString *localIdentifier;

@end  

现在不使用图像数组,而是使用您创建的包含localIdentifier的自定义类.像这样:

PhotoInfo *photo = [[PhotoInfo alloc] init];
photo.localIdentifier = asset.localIdentifier;

假设您想要从图库中获取图像,您可以执行以下操作:

-(PHFetchResult*) getAssetsFromLibrary
{
    PHFetchResult *allPhotos;
    PHFetchOptions *allPhotosOptions = [[PHFetchOptions alloc] init];
    allPhotosOptions.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:NO]]; //Get images sorted by creation date

    allPhotos = [PHAsset fetchAssetsWithMediaType:PHAssetMediaTypeImage options:allPhotosOptions];

    return allPhotos;
}

要填充dataSource,您可以执行以下操作:

NSMutableArray *yourPhotoDataSource = [[NSMutableArray alloc] init];
PHFetchResult * assets = [self getAssetsFromLibrary];
 for(PHAsset *asset in assets)
        {
            PhotoInfo *photo = [PhotoInfo new];
            photo.localIndentifier = asset.localIdentifier;
            [yourPhotoDataSource addObject:photo];

        }

现在让我们假设您必须在某处显示这些图像,并且您需要一个实际图像,以便您可以执行以下操作来获取图像:

-(void) getImageForAsset: (PHAsset *) asset andTargetSize: (CGSize) targetSize andSuccessBlock:(void (^)(UIImage * photoObj))successBlock {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        PHImageRequestOptions *requestOptions;

        requestOptions = [[PHImageRequestOptions alloc] init];
        requestOptions.resizeMode   = PHImageRequestOptionsResizeModeFast;
        requestOptions.deliveryMode = PHImageRequestOptionsDeliveryModeFastFormat;
        requestOptions.synchronous = true;
        PHImageManager *manager = [PHImageManager defaultManager];
        [manager requestImageForAsset:asset
                           targetSize:targetSize
                          contentMode:PHImageContentModeDefault
                              options:requestOptions
                        resultHandler:^void(UIImage *image, NSDictionary *info) {
                            @autoreleasepool {

                                if(image!=nil){
                                    successBlock(image);
                                }
                            }
                        }];
    });

}

现在假设您正在tableView中显示这些图像,在您的cellForRowAtIndexPath中,调用上面提到的方法如下:

  //Show a spinner
  // Give a customizable size for image. Why load the memory with full image if you don't need to show it?
 [self getImageForAsset:asset andTargetSize:yourDesiredCGSizeOfImage andSuccessBlock:^(UIImage *photoObj) {
            dispatch_async(dispatch_get_main_queue(), ^{
                //Update UI of cell
                //Hide the spinner
                cell.thumbNail.image = photoObj;
            });
        }];

现在,您可以通过平滑的用户体验异步加载图像,并通过仅显示所需的图像而不是存储所有图像来节省内存.(通过引入缓存可以使性能更好,但这不是重点).

最后回答您的问题,要删除某个图像,您只需要localIdentifier,因为它对每个PHAsset或Index都是唯一的.

假设您正在删除tableView上的某个单元格,该单元格显示您现在要删除的特定图像.

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {

if (editingStyle == UITableViewCellEditingStyleDelete) {
    PhotoInfo *photo = [yourPhotoDataSource objectAtIndex:indexPath.row];
    [yourPhotoDataSource removeObject:photo];
    [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                     withRowAnimation:UITableViewRowAnimationFade];


}
}

如果您没有使用TableView/CollectionView并且不知道对象的索引,则可以在数组上使用快速枚举,但是您必须知道要删除的对象的localIdentifier:

-(void) deletePhotoWithIdentifier:(NSString *) identifierStr{
NSMutableArray *dummyArray = [[NSMutableArray alloc] initWithArray:yourPhotoDataSource]; //created because we can't modify the array we are iterating on. Otherwise it crashes. 
[dummyArray enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(PhotoInfo *p, NSUInteger index, BOOL *stop) {
    if ([p.localIndentifier isEqualToString:idenfierStr]) {
        [yourPhotoDataSource removeObjectAtIndex:index];
    }
}];

}