How can i get original nsdata of uiimage?

问题:

In my app, user can select a pic from album or camera where i can get uiimage representation. Since the album may have pic from web, the file type is not only jpg. Then i need to sent it to the server without convertion. Here i can only use nsdata.
I know UIImageJPEGRepresentation and UIImagePNGRepresentation, but i think this two method may convert the original image. Maybe when quality set to 1 UIImageJPEGRepresentation can get original pic?
Is there any method to get the original uiimage nsdata?

回答1:

You can use the ALAssetsLibrary and ALAssetRepresentation to get the original data. Example:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    NSURL *imageURL = [info objectForKey:UIImagePickerControllerReferenceURL];
    ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];
    [library assetForURL:imageURL resultBlock:^(ALAsset *asset) {
        ALAssetRepresentation *repr = [asset defaultRepresentation];
        NSUInteger size = repr.size;
        NSMutableData *data = [NSMutableData dataWithLength:size];
        NSError *error;
        [repr getBytes:data.mutableBytes fromOffset:0 length:size error:&error];
            /* Now data contains the image data, if no error occurred */
    } failureBlock:^(NSError *error) {
        /* handle error */
    }];
}

But there are some things to consider:

• assetForURL: works asynchronously.
• On the device, using assetForURL: will cause a confirmation dialog, which might be irritating the user:

"Your App" would like to use your current location. This allows access to location information in photos and videos.

• If the user denies access, assetForURL: calls the failure block.
• The next time you use this method, assetForURL: will fail without asking the user again. Only if you reset the location warnings in System Settings, the user is asked again.

So you should be prepared that this method fails and use UIImageJPEGRepresentation or UIImagePNGRepresentation as a fallback. But in that case you will not get the original data, e.g. the metadata (EXIF etc.) are missing.

回答2:

On iOS 8.0+ use PHImageManager.default().requestImageData() after you locate the corresponding asset in the assets (you can get to assets with PHAsset.fetchAssets().

See more info and example code in my answer to very similar question How to upload image that was taken from UIImagePickerController.