当参数具有默认值时，为什么我不能使用导航组件将参数传递给片段？

Question

I am using navigation component and I don't understand why I get an error passing the argument to the method below if the argument is defined. I am using SafeArgs and I only get this error when I define a default value for this argument.

Could someone explain me why this happens and how can I solve it?

Here is a part of the code of the navigation graph.

<fragment
        android:id="@+id/sleepTrackerFragment"
        android:name="com.example.sleeptracker.fragments.sleep_tracker.SleepTrackerFragment"
        android:label="fragment_sleep_tracker"
        tools:layout="@layout/fragment_sleep_tracker" >
        <action
            android:id="@+id/action_sleepTrackerFragment_to_sleepQualityFragment"
            app:destination="@id/sleepQualityFragment" />
        <argument
            android:name="qualityLastSleep"
            app:argType="integer"
            android:defaultValue="-1" />
    </fragment>
    <fragment
        android:id="@+id/sleepQualityFragment"
        android:name="com.example.sleeptracker.fragments.sleep_quality.SleepQualityFragment"
        android:label="fragment_sleep_quality"
        tools:layout="@layout/fragment_sleep_quality" >
        <action
            android:id="@+id/action_sleepQualityFragment_to_sleepTrackerFragment"
            app:destination="@id/sleepTrackerFragment" >
        </action>
    </fragment>

Answer 1

seems like what you really want is destination level argument:

Try the following:

<fragment
        android:id="@+id/sleepTrackerFragment"
        android:name="com.example.sleeptracker.fragments.sleep_tracker.SleepTrackerFragment"
        android:label="fragment_sleep_tracker"
        tools:layout="@layout/fragment_sleep_tracker" >
        <action
            android:id="@+id/action_sleepTrackerFragment_to_sleepQualityFragment"
            app:destination="@id/sleepQualityFragment" />
    </fragment>
    <fragment
        android:id="@+id/sleepQualityFragment"
        android:name="com.example.sleeptracker.fragments.sleep_quality.SleepQualityFragment"
        android:label="fragment_sleep_quality"
        tools:layout="@layout/fragment_sleep_quality" >
        <action
            android:id="@+id/action_sleepQualityFragment_to_sleepTrackerFragment"
            app:destination="@id/sleepTrackerFragment" >
            <argument
               android:name="qualityLastSleep"
               app:argType="integer"
               android:defaultValue="-1" />
        </action>
    </fragment>

You can also Ctrl+Click on actionSleepQualityFragmentToSleepTrackerFragment() to check if the generated function accepts an argument.

Do try clean and rebuild if IDE complains about argument passing

Doc link: https://developer.android.com/guide/navigation/navigation-pass-data#override_a_destination_argument_in_an_action

Let me know if this does not work for you

Answer 2

As mentioned in documentation

Destination-level arguments and default values are used by all actions that navigate to the destination. If needed, you can override the default value of an argument (or set one if it doesn't already exist) by defining an argument at the action level. This argument must be of the same name and type as the argument declared in the destination.

so you have to override this value to do so you can follow any of the both solutions below

solution one

 val action =  SleepQualityFragmentDirections.actionSleepQualityFragmentToSleepTrackerFragment()
 action.qualityLastSleep = 5 // your value
 findNavController().navigate(action)

---

solution two

<fragment
    android:id="@+id/sleepTrackerFragment"
    android:name="com.example.sleeptracker.fragments.sleep_tracker.SleepTrackerFragment"
    android:label="fragment_sleep_tracker"
    tools:layout="@layout/fragment_sleep_tracker" >
   <argument
           android:name="qualityLastSleep"
           app:argType="integer"
           android:defaultValue="-1" />
    <action
        android:id="@+id/action_sleepTrackerFragment_to_sleepQualityFragment"
        app:destination="@id/sleepQualityFragment" />
</fragment>
<fragment
    android:id="@+id/sleepQualityFragment"
    android:name="com.example.sleeptracker.fragments.sleep_quality.SleepQualityFragment"
    android:label="fragment_sleep_quality"
    tools:layout="@layout/fragment_sleep_quality" >
    
    <action
        android:id="@+id/action_sleepQualityFragment_to_sleepTrackerFragment"
        app:destination="@id/sleepTrackerFragment" >
     <argument
           android:name="qualityLastSleep"
           app:argType="integer"
           android:defaultValue="-1" />
       
    </action>
</fragment>

and then you can call your navigation like this

findNavController().navigate(SleepQualityFragmentDirections.actionSleepQualityFragmentToSleepTrackerFragment(5))