碰到一個問題：如何快速的批量儲存iphone相簿中的圖片（原始的大圖，解析度高）到本地？

儲存圖片到本地，首先得拿到這個圖片：alAsset.defaultRepresentation.fullResolutionImage.但是圖片太大了，大批量的儲存取這個圖片就得花很長的時間，再轉NSData存入本地又得很久，所以這種讀寫方式是不行的。

      我google了一下，在stack overflow找到了方法：點選開啟連結 。

      我把實現的方法貼一下（包括大圖和縮圖）：

//reading out the orginal images
    for (int j=0; j<[assetArray count]; j++) {

    ALAssetRepresentation *representation = [[assetArray objectAtIndex:j] defaultRepresentation];
    NSString* filename = [documentPath stringByAppendingPathComponent:[representation filename]];

    [[NSFileManager defaultManager] createFileAtPath:filename contents:nil attributes:nil];
    NSOutputStream *outPutStream = [NSOutputStream outputStreamToFileAtPath:filename append:YES];
    [outPutStream open];

    long long offset = 0;
    long long bytesRead = 0;

    NSError *error;
    uint8_t * buffer = malloc(131072);
    while (offset<[representation size] && [outPutStream hasSpaceAvailable]) {
        bytesRead = [representation getBytes:buffer fromOffset:offset length:131072 error:&error];
        [outPutStream write:buffer maxLength:bytesRead];
        offset = offset+bytesRead;
    }
    [outPutStream close];
    free(buffer);
}


//reading out the fullScreenImages and thumbnails
for (int j=0; j<[assetArray count]; j++) 
{
    @autoreleasepool
    {

        ALAsset *asset = [assetArray objectAtIndex:j];

         NSString *orgFilename = [representation filename];
         NSString *filenameFullScreen = [NSString stringWithFormat:@"%@_fullscreen.png",[orgFilename stringByDeletingPathExtension]]
         NSString* pathFullScreen = [documentPath stringByAppendingPathComponent:filenameFullScreen];

         CGImageRef imageRefFullScreen = [[asset defaultRepresentation] fullScreenImage];
         UIImage *imageFullScreen = [UIImage imageWithCGImage:imageRefFullScreen];
         NSData *imageDataFullScreen = UIImagePNGRepresentation(imageFullScreen);
         [imageDataFullScreen writeToFile:pathFullScreen atomically:YES];

         NSString *filenameThumb = [NSString stringWithFormat:@"%@_thumb.png",[orgFilename stringByDeletingPathExtension]]
         NSString* pathThumb = [documentPath stringByAppendingPathComponent:filenameThumb];

         CGImageRef imageRefThumb = [asset thumbnail];
         UIImage *imageThumb = [UIImage imageWithCGImage:imageRefThumb];
         NSData *imageDataThumb = UIImagePNGRepresentation(imageThumb);
         [imageDataThumb writeToFile:pathThumb atomically:YES];

    }
}
 

參考：http://stackoverflow.com/questions/9973259/what-is-the-correct-way-to-import-save-photos-from-iphone-album