Open a custom type of file from mail attachment

Hello folks!

This is a copy-paste of a question I first asked on StackOverflow, I hope that maybe someone here would know the answer ^^ I’ll keep both posts here and on SO updated if I find the solution to my problem :wink:

I’m developing a small Ionic app that needs some data to be processed and displayed in a certain way. The data are originally stored in a file under XLSX format, then the file’s extension is changed to a custom one, let’s say .myext (for those who wonder: I do that so all .xlsx files are not automatically opened with my app, which needs a certain data structuration).

I managed, like you can see in a previous post I made about this app on StackOverflow, to make my app able to open XLSX files, and then able to open .myext files. Though, I can only open a .myext file with my app automatically when opening it via a file system explorer on my Android device (in my case File Commander). I want the device to automatically open .myext files with my app when the user receive such file in his/her mail inbox (whether dedicated app or browser); when I try to do so, I got a warning saying that no app capable to open such files is available on my device (the file is downloaded anyway and I still can open it via device file system explorer).

I tried to change my intent declaration in the AndroidManifest, without any luck for now (note the android:scheme lines; I tried several combinations, using one, two, three, or all of them at the same time):

<activity android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale" android:label="@string/activity_name" android:launchMode="singleTop" android:name="MainActivity" android:theme="@android:style/Theme.Black.NoTitleBar" android:windowSoftInputMode="adjustResize">
    <intent-filter android:label="@string/launcher_name">
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />
        <data android:scheme="file" />
        <data android:scheme="http" />
        <data android:scheme="https" />
        <data android:scheme="content" />
        <data android:mimeType="*/*" />
        <data android:pathPattern=".*\\.myext" />
        <data android:host="*" />

I feel like I’m missing something, or that is not possible to open custom file extension via mail attachment. Do you have any idea to do so?