How are Intent-Categories matched?

Question

I don't get the Android Intent matching concept! I must be missing something, but I read and re-read the docs and don't get it. Maybe some kind soul can shed some light on this?

I am able to start an Activity if I specify a Category filter "android.intent.category.DEFAULT" in the manifest:

    ...
    <activity 
        android:name="mmmo.android.test.ItemDetails"
        <intent-filter>
            <action android:name="android.intent.action.INSERT" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>
    ...

and if I then don't add any Category to the Intent object:

        ...
        Intent intent = new Intent(Intent.ACTION_INSERT);
        startActivity(intent);
        ...

That works. However, as soon as I define any other category than "android.intent.category.DEFAULT" I am only getting ActivityNotFoundExceptions. E.g. if I specify:

    ...
    <activity 
        android:name="mmmo.android.test.ItemDetails"
        <intent-filter>
            <action android:name="android.intent.action.INSERT" />
                    <category android:name="foo.bar" />
        </intent-filter>
    </activity>
    ...

and then try to start that Activity using:

        ...
        Intent intent = new Intent(Intent.ACTION_INSERT);
        intent.addCategory("foo.bar"); 
        startActivity(intent);
        ...

this does not work. The doc reads "... every category in the Intent object must match a category in the filter. ...". The category name I add to the Intent matches the category I specified in the filter. So why does this not match up and just throws an exception???

Michael

Answer 1

You must also add

 <category android:name="android.intent.category.DEFAULT"></category>

to the intent filter for the intent to be resolved.

See Intent:

Activities will very often need to support the CATEGORY_DEFAULT so that they can be found by Context.startActivity().