Automatically trigger pipeline by new Docker images in Google Artifact Registry (GAR)

Hi community,

I am new to Azure DevOps. I want to build a pipeline that is automatically triggered by Google Artifact Registry (GAR, not by Azure Container Registry or Docker Hub). Is that possible? I am following this document. I have tried many times, changed a lot of formats, variables and still cannot get it done correctly. So I want to know if a pipeline can be triggered when a new image is pushed to GAR or not? If so, how should I set it up? 

Thanks!