为什么在导航中切换屏幕时不能将 null 作为参数？

Question

我用navigation和SafeArgs到switch screens和pass data。

在屏幕上选择数据时A，数据在屏幕切换的同时传输。

但是，有时屏幕 A 会在没有任何操作的情况下切换到屏幕 B。

我决定在这种情况下发送null。

但我不断收到以下错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.lightweight, PID: 9555
    java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130) 
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at androidx.navigation.NavArgsLazy.getValue(NavArgsLazy.kt:54)
        at androidx.navigation.NavArgsLazy.getValue(NavArgsLazy.kt:35)
        at com.example.lightweight.fragment.WriteRoutineFragment.getArgs(WriteRoutineFragment.kt:20)
        at com.example.lightweight.fragment.WriteRoutineFragment.onViewCreated(WriteRoutineFragment.kt:44)
        at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2985)

navigation.xml

<fragment
        android:id="@+id/writeRoutine"
        android:name="com.example.lightweight.fragment.WriteRoutineFragment"
        android:label="fragment_write_routine"
        tools:layout="@layout/fragment_write_routine" >
        <action
            android:id="@+id/action_writeRoutineFragment_to_workoutListTabFragment"
            app:destination="@id/workoutListTabFragment" />
        <argument
            android:name="workout"
            app:argType="string"
            app:nullable="true" />
</fragment>

在适配器中

inner class ViewHolder(itemView: View, context: Context) : RecyclerView.ViewHolder(itemView) {
        private val tv: TextView = itemView.findViewById(R.id.workout)

        init {
            tv.setOnClickListener { view ->
                val workout = tv.text.toString()
                val action: NavDirections = WorkoutListTabFragmentDirections.actionWorkoutListTabToWriteRoutine(workout)
                view.findNavController().navigate(action)
            }
        }

        fun bind(item: String) {
            tv.text = item
        }
    }

这是什么原因？

Answer 1

您应该添加解决方法参数的默认值。这里因为设置了app:nullable="true"，所以应该设置android:defaultValue="@null".

修改创建解决方法参数的方式如下：

<argument
   android:name="workout"
   app:argType="string"
   android:defaultValue="@null"
   app:nullable="true" />

更多信息：Supported argument types - Navigation

为什么在导航中切换屏幕时不能将 null 作为参数？

Why can't I get null as an argument when switching screens in navigation?

android

android-navigation

android-navigation-graph

android-safe-args