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我已经实现了一种使用 Alassetslibrary 正确检索图像信息的方法。如您所知，它是异步工​​作的，但在我的情况下，我需要它同步工作。我只需阅读有关图像的信息并返回该方法。我的应用程序只是一个不需要刷新的视图。如何修改我的方法？目前这行“return xmlList;” 结果始终为空，但我知道资产在块中被正确读取，因为我使用了 NSlog。

-(NSString *) getPhotos{

NSMutableArray *idList = [[NSMutableArray alloc] init];
NSMutableArray *widthList = [[NSMutableArray alloc] init];
NSMutableArray *heightList = [[NSMutableArray alloc] init];
NSMutableArray *orientationList = [[NSMutableArray alloc] init];
NSMutableArray *dateList = [[NSMutableArray alloc] init];

__block XMLWriter* xmlWriter = [[XMLWriter alloc]init];
__block NSString *xmlList;
__block NSString *test;
__block ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
__block NSString *description = [[NSString alloc] init];
[library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    if (group) {
        [group setAssetsFilter:[ALAssetsFilter allPhotos]];
        [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop){
            if (asset){
                NSString *description = [asset description];
                NSRange first = [description rangeOfString:@"URLs:"];
                NSRange second = [description rangeOfString:@"?id="];
                NSString *path = [description substringWithRange: NSMakeRange(first.location + first.length, second.location - (first.location + first.length))];
                [idList addObject:path];

                NSDictionary *data = [[asset defaultRepresentation] metadata];

                NSNumber *width = [[[asset defaultRepresentation] metadata] objectForKey:@"PixelWidth"];
                NSString *widthString = [NSString stringWithFormat:@"%@", width];
                [widthList addObject:widthString];

                NSNumber *height = [[[asset defaultRepresentation] metadata] objectForKey:@"PixelHeight"];
                NSString *heightString = [NSString stringWithFormat:@"%@", height];
                [heightList addObject:heightString];

                NSNumber *orientation = [[[asset defaultRepresentation] metadata] objectForKey:@"Orientation"];
                NSString *orientationString = [NSString stringWithFormat:@"%@", orientation];
                if(orientationString != NULL){
                    [orientationList addObject:orientationString];
                } else {
                    NSString *noOrientation = [[NSString alloc] init];
                    noOrientation = @"No orientation avaiable";
                    [dateList addObject:noOrientation];
                }

                NSString *dateString = [[[asset defaultRepresentation] metadata] objectForKey:@"DateTime"];
                if(dateString != NULL){
                    [dateList addObject:dateString];
                } else {
                    NSString *noDate = [[NSString alloc] init];
                    noDate = @"No date avaiable";
                    [dateList addObject:noDate];
                }
            }
        }];
    }
    if (group == nil){
        [xmlWriter writeStartDocumentWithEncodingAndVersion:@"UTF-8" version:@"1.0"];
        [xmlWriter writeStartElement:@"Data"];
        int i = 0;
        for(i = 0; i<=[idList count]-1; i++){
            [xmlWriter writeStartElement:@"Photo"];
            [xmlWriter writeAttribute:@"Id" value:[idList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Width" value:[widthList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Height" value:[heightList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Orientation" value:[orientationList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Date" value:[dateList objectAtIndex:i]];
            [xmlWriter writeEndElement:@"Photo"];
        }
        [xmlWriter writeEndElement:@"Data"];
        [xmlWriter writeEndDocument];
        xmlList = [xmlWriter toString];
    }

} failureBlock:^(NSError *error) {
    NSLog(@"error enumerating AssetLibrary groups %@\n", error);
}];

return xmlList;

}
4

1 回答 1

0

好的，最后我已经解决了我的问题。我使用了 NSConditionLock 类。这里有更新的代码：

-(NSString *) getPhotos{
enum { WDASSETURL_PENDINGREADS = 1, WDASSETURL_ALLFINISHED = 0};
NSMutableArray *idList = [[NSMutableArray alloc] init];
NSMutableArray *widthList = [[NSMutableArray alloc] init];
NSMutableArray *heightList = [[NSMutableArray alloc] init];
NSMutableArray *orientationList = [[NSMutableArray alloc] init];
NSMutableArray *dateList = [[NSMutableArray alloc] init];

__block XMLWriter* xmlWriter = [[XMLWriter alloc]init];
__block NSString *xmlList;
__block NSString *test;

__block NSConditionLock * assetsReadLock = [[NSConditionLock alloc] initWithCondition:WDASSETURL_PENDINGREADS];
dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
__block ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
__block NSString *description = [[NSString alloc] init];
[library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    if (group) {
        [group setAssetsFilter:[ALAssetsFilter allPhotos]];
        [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop){
            if (asset){
                NSString *description = [asset description];
                NSRange first = [description rangeOfString:@"URLs:"];
                NSRange second = [description rangeOfString:@"?id="];
                NSString *path = [description substringWithRange: NSMakeRange(first.location + first.length, second.location - (first.location + first.length))];
                [idList addObject:path];

                NSDictionary *data = [[asset defaultRepresentation] metadata];

                NSNumber *width = [[[asset defaultRepresentation] metadata] objectForKey:@"PixelWidth"];
                NSString *widthString = [NSString stringWithFormat:@"%@", width];
                [widthList addObject:widthString];

                NSNumber *height = [[[asset defaultRepresentation] metadata] objectForKey:@"PixelHeight"];
                NSString *heightString = [NSString stringWithFormat:@"%@", height];
                [heightList addObject:heightString];

                NSNumber *orientation = [[[asset defaultRepresentation] metadata] objectForKey:@"Orientation"];
                NSString *orientationString = [NSString stringWithFormat:@"%@", orientation];
                if(orientationString != NULL){
                    [orientationList addObject:orientationString];
                } else {
                    NSString *noOrientation = [[NSString alloc] init];
                    noOrientation = @"No orientation avaiable";
                    [dateList addObject:noOrientation];
                }

                NSString *dateString = [[[asset defaultRepresentation] metadata] objectForKey:@"DateTime"];
                if(dateString != NULL){
                    [dateList addObject:dateString];
                } else {
                    NSString *noDate = [[NSString alloc] init];
                    noDate = @"No date avaiable";
                    [dateList addObject:noDate];
                }
            }
        }];
    }
    if (group == nil){
        [xmlWriter writeStartDocumentWithEncodingAndVersion:@"UTF-8" version:@"1.0"];
        [xmlWriter writeStartElement:@"Data"];
        int i = 0;
        for(i = 0; i<=[idList count]-1; i++){
            [xmlWriter writeStartElement:@"Photo"];
            [xmlWriter writeAttribute:@"Id" value:[idList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Width" value:[widthList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Height" value:[heightList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Orientation" value:[orientationList objectAtIndex:i]];
            [xmlWriter writeAttribute:@"Date" value:[dateList objectAtIndex:i]];
            [xmlWriter writeEndElement:@"Photo"];
        }
        [xmlWriter writeEndElement:@"Data"];
        [xmlWriter writeEndDocument];
        xmlList = [xmlWriter toString];
        [assetsReadLock lock];
        [assetsReadLock unlockWithCondition:WDASSETURL_ALLFINISHED];
    }

} failureBlock:^(NSError *error) {
    NSLog(@"error enumerating AssetLibrary groups %@\n", error);
    [assetsReadLock lock];
    [assetsReadLock unlockWithCondition:WDASSETURL_ALLFINISHED];
}];
});

[assetsReadLock lockWhenCondition:WDASSETURL_ALLFINISHED];
[assetsReadLock unlock];
NSLog(@"XML: %@", xmlList);
return xmlList;

}
于 2013-08-28T09:45:29.030 回答