I can't install apk file: App Not Installed I recently got a HTC One M9, and I wanted to replace it's gallery with my old phone's gallery because I loved one of the filters that it had. This led to me having to download a third party APK file, but when I tried to install it, it just gave me an error that said "App not installed." I first thought it's because it won't install because the current gallery is still on my phone, but after disabling the app, I still get the error message. Is there any way I can fix this?

The APK file is MIUI's Gallery app if that helps.
Generally you can't install one manufacturer's built-in apps on another manufacturer's phone anyway. The built-in apps are written to take advantage of the specific hardware on that phone and/or extra libraries the manufacturer includes in their system image. Camera apps are a particularly bad culprit because often they rely on the features of the camera chip and on a custom image-processing library.

As well as the technical problems, this is software piracy. The app is made by the phone manufacturer to give that particular phone a competitive advantage. It's only licensed for use on that phone. It's not like on Google Play where you buy an app and then can use it on any phone.