Why is no Activity found to handle Intent?

Question

Instead of going the regular getPackageManager().getLaunchIntentForPackage("com.example.app") way, I want to create the launch intent by myself.

Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
intent.setPackage("com.example.app");
startActivity(intent);

Why does Android not find the Activity, if the com.example.app is installed, enabled and has a correct manifest? (It works perfectly with getLaunchIntentForPackage.)

Answer 1

I understand that you are trying to start the Launcher activity of a known application with known package name (com.example.app). I assume you have information about the application. Thus, you can start it via explicit intent like so:

Intent intent = new Intent();
intent.setComponent(new ComponentName("com.example.app", "com.example.app.MainActivity"));
if(intent.resolveActivity(getPackageManager()) != null) {
    startActivity(intent);
}

EDIT: Doing an analysis of the two intent objects (intent1 == your own intent VS intent2 == intent created from getLaunchIntentForPackage()), the difference is

intent1:

{ act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] pkg=com.example.app }

intent2:

{ act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 pkg=com.example.app cmp=com.example.app/.MainActivity }

I will have to believe that what you have done to create your own intent object is not enough for the explicit intent to work. You will have to provide Android more information about your intent such as being specific with the component name (as shown in my answer above).

Answer 2

'To receive implicit intents, you must include the CATEGORY_DEFAULT category in the intent filter.' - Does your receiving app have this?

Example:

<activity android:name="ShareActivity">
     <intent-filter>
         <action android:name="android.intent.action.SEND"/>
         <category android:name="android.intent.category.DEFAULT"/>
         <data android:mimeType="text/plain"/>
     </intent-filter>
</activity>

Excerpt from: https://developer.android.com/guide/components/intents-filters#Receiving

You can also check to make sure there is an activity that can receive your broadcast:

 PackageManager packageManager = getPackageManager();
 List<ResolveInfo> activities = packageManager.queryIntentActivities(intent,PackageManager.MATCH_DEFAULT_ONLY);
 boolean isIntentSafe = activities.size() > 0;

Excerpt from: https://developer.android.com/training/basics/intents/sending#java