[Xamarin.Android.Build.Tasks] emit exported="true" for MainLauncher activities

[jonathanpeppers]

Context: https://aster.cloud/2021/02/23/lets-be-explicit-about-our-intent-filters/
Fixes: #6196

An important change is coming to Android 12 that improves both app
and platform security. This change affects all apps that target
Android 12.

Activities, services, and broadcast receivers with declared
intent-filters now must explicitly declare whether they should be
exported or not.

For example:

<activity android:icon="@mipmap/icon" android:label="HelloWorld" android:name="example.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

Should become:

<activity android:exported="true" android:icon="@mipmap/icon" android:label="HelloWorld" android:name="example.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

Update our AndroidManifest.xml generation & related code so that
when MainLauncher=true, we also automatically set exported=true.

I updated a test to verify the contents of the generated
AndroidManifest.xml.

[jonpryor]

@jonathanpeppers wrote:

For example:

<activity android:icon="@mipmap/icon" android:label="HelloWorld" android:name="example.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

Should become:

<activity android:icon="@mipmap/icon" android:label="HelloWorld" android:name="example.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" android:exported="true" />
    <category android:name="android.intent.category.LAUNCHER" android:exported="true" />
  </intent-filter>
</activity>

I don't think this is correct. There is no //action/@android:exported attribute (<action/> docs), nor is there a //category/@android:exported attribute (<category/> docs). Nor is there an //intent-filter/@android:exported attribute, not that you're using one (<intent-filter/> docs).

What you should be emitting is the //activity/@android:exported attribute, which is documented.

Thus, you should be emitting:

<activity android:exported="true" android:icon="@mipmap/icon" android:label="HelloWorld" android:name="example.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

This also matches the blog post you linked to:

<activity
    android:name=”.PlayVideoActivity”
    android:exported=”false”>
    <intent-filter>
        <action android:name=”android.intent.action.VIEW” />
        <data
            android:mimeType=”video/*”
            android:scheme=”content” />
    </intent-filter>
</activity>

[jonathanpeppers]

<activity android:exported="true" android:icon="@mipmap/icon" android:label="HelloWorld" android:name="example.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

Thanks, I don't know how I got confused about the wrong element before.

Now I get:

    <activity android:icon="@mipmap/icon" android:label="HelloWorld" android:name="example.MainActivity" android:exported="true">
      <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
      </intent-filter>
    </activity>
    <activity android:label="Library Activity" android:name="mono.samples.hello.LibraryActivity" />

[alihamie]

Do we want to add this for all Android versions or should we only be doing it for Android 12 + ?

[jonathanpeppers]

It does not appear that //activity/@android:exported attribute has a minimum API level. Since this is a security feature, we're probably good to set this across the board?

Usually the way new attributes work in AndroidManifest.xml, is that older Android versions just ignore the values they don't know about.

[alihamie]

oh okay awesome then ! thank you