fix display problems when image fails to load

[jsfu]

Summary

When the image resource is changed and the new image resource fails to load, we expect the display image to fail to load, but the image still shows the image that was successfully loaded last time.

Changelog

[iOS] [Fixed] - fix display problems when image fails to load

Test Plan

I found that the old image resource of ImageView was not cleaned up when the image failed to load, so I added the cleanup of the old resource in the logic of image loading failure.

- (void)imageLoaderLoadedImage:(UIImage *)loadedImage error:(NSError *)error forImageSource:(RCTImageSource *)source partial:(BOOL)isPartialLoad
{
  if (![source isEqual:_pendingImageSource]) {
    // Bail out if source has changed since we started loading
    return;
  }

  if (error) {
    if (_onError) {
      _onError(@{ @"error": error.localizedDescription });
    }
    if (_onLoadEnd) {
      _onLoadEnd(nil);
    }
    return;
  }
  ……
}

Before fix：

After fix:

[sammy-SC]

Could you explain me why this condition is necessary? I am having hard time understanding why it is needed.

Otherwise
You can get rid of . absoluteString as NSURL has isEqual defined (https://developer.apple.com/documentation/foundation/nsurl/1806686-isequal?language=objc).

Also I don't think we have to check whether _pendingImageSource.request and _imageSource.request are nils.

[jsfu]

I think the Image should really show whether the image is loaded successfully. If the loading fails and the URL is not equal to the previous one, then the previous image should not be displayed again, because the developer expects to display the new image, But the new image fails to load. . Usually developers can use onError's callbacks to handle failures, but when the developer doesn't handle the error, the image displayed is actually wrong.

Also, thank you for your suggestion. I got a new skill : )

[sammy-SC]

Thank you for taking your time to work on this!

[facebook-github-bot]

@sammy-SC has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by jsfu in 71d7d68.

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