正确的进口方式是什么；从iPhone相册中保存照片？

我正在将照片从iPhone相册导入应用程序的documents文件夹。这是我的密码

for (int j=0; j<[assetArray count]; j++) {

    ALAsset *assest = [assetArray objectAtIndex:j];
    CGImageRef imageRef = assest.defaultRepresentation.fullResolutionImage;
    UIImage *image = [UIImage imageWithCGImage:imageRef];
    NSData *imageData = UIImageJPEGRepresentation(image);
    [imageData writeToFile:documentsPath atomically:YES];
}

---

for（int j=0；j我使用的是ELCImagePicker，在使用asselts从照片库一次导入多张照片时遇到了相同的问题。我们无法减少导入所需的时间，但崩溃问题将得到解决

for (int j=0; j<[assetArray count]; j++) 
{
    @autoreleasepool // This is compiler level feature so will only work on xcode 4.1 or above
    {
         ALAsset *assest = [assetArray objectAtIndex:j];
         CGImageRef imageRef = assest.defaultRepresentation.fullResolutionImage;
         UIImage *image = [UIImage imageWithCGImage:imageRef];
         NSData *imageData = UIImagePNGRepresentation(image);
         [imageData writeToFile:documentsPath atomically:YES];
    }
}

出于以下几个原因，将fullResolutionImage用于此任务是危险的。
一些评论：

对于大型图像，可能会出现内存问题。使用fullResolutionImage方法时。请注意，照片库（至少在iPad上）也可能包含原始图像
性能不太理想，因为从imagefile ImageIO内部首先创建一个CGImageRef，然后将其转换为JPEG。这需要时间
资产库还可以包含视频。在这种情况下，fullResolutionImage只返回视频的预览图像，而不返回实际视频
存储实际的资产对象没有问题，因为它们在内存中很小
将图像写入documents目录的更好方法是使用AlassetRepresentation的getBytes方法。这应该更快、更高效。它还提供原始图像文件（包括元数据），也适用于视频

然后重写的示例代码如下所示：

//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];

    }
}

//读取原始图像
对于（int j=0；jWe可以缩短时间。我看到这个应用程序导入速度非常快。在设备而不是模拟器中导入照片需要多少时间？请添加更多细节，如照片数量分辨率？autoreleasepool修复了崩溃…谢谢..但我不知道如何缩短时间…我已经测试了导入时间taken用上面的代码导入1.7 MB大小的文件大约需要2到2.3秒。对于大小不同的2个文件（1.7 MB和0.8 MB），最长4秒也有同样的问题，但我通过将资源URL保存在数据库中解决了这个问题。当我需要在documents目录中存储图像时，我会逐个获取资源并将图像存储在documents目录中。一个原因可能是您正在将资产保存在数组save asset url中，还有一件事是在自动释放池中运行此for循环，这将减少内存问题。谢谢您，它工作得非常好。但是我如何将缩略图和全屏图像复制到documents文件夹？或者是否有其他方法可以从集合中获取这些图像S文档文件夹中的演示文稿？我修改了源代码，包括读取全屏图像和缩略图。对于这两幅图像，您可以使用以前的方法，因为它们的大小有限，与fullResolutionImage相比，只消耗可预测的内存量。根据您想做的事情，您可能会考虑呃，将全屏图像保存为JPEG而不是PNG，但这只是一个小的代码更改。谢谢。我们的应用程序一直崩溃，但现在没有。documentPath在这里是什么
//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];

    }
}