当该参数具有默认值时，为什么我不能使用导航组件将参数传递给片段? [英] Why can't I pass an argument to fragment using navigation component when that argument has a default value?

问题描述

我正在使用导航组件，但我不明白为什么如果定义了参数，我会在将参数传递给下面的方法时出现错误.我正在使用 SafeArgs，但只有在为此参数定义默认值时才会出现此错误.

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.

谁能解释一下为什么会发生这种情况，我该如何解决?

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

这是导航图的一部分代码.

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>

推荐答案

如文档中所述

目标级别的参数和默认值由导航到目标的所有操作使用.如果需要，您可以通过在操作级别定义参数来覆盖参数的默认值(如果尚不存在则设置一个).此参数必须与目标中声明的参数具有相同的名称和类型.

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.

因此您必须覆盖此值才能执行以下任一解决方案

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

解决方案一

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

---

方案二

<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>

然后你可以像这样调用你的导航

and then you can call your navigation like this

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

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