我对Android，Java和Kotlin都很陌生，我正在尝试将我的应用程序移植到Swift上，它最初是为iOS编写的。

应用程序使用的数据是我的Speaker对象的ArrayList，来自一个JSON文件。

我的MainActivity显示一个由每个扬声器的“brand”参数填充的RecyclerView。 每一行的onClick启动BrandMenuActivity，并使用一个带有该品牌所有扬声器的RecycerView。 然后，它们的onClick显示了一个DetailView。

当使用模拟器中的“Hardware”back按钮导航时，一切都很正常，但是如果我尝试在detailView的操作栏中实现setDisplayHomeAsUpEnabled，应用程序就会崩溃，因为BrandMenuActivity的意图现在为null。

我的AndroidManifest:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.speakerskotlin">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".SpeakerDetailActivity"
        android:parentActivityName=".BrandMenuActivity">
    </activity>
    <activity android:name=".BrandMenuActivity"
        android:parentActivityName=".MainActivity" >
    </activity>
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

主要活动:

class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    setSupportActionBar(findViewById(R.id.speakerToolbar))
    supportActionBar?.title = "Speakers"
    
    val jsonFileString = getJsonDataFromAsset(applicationContext, "SpeakerData.json")

    val gson = Gson()
    val listSpeakerType = object : TypeToken<ArrayList<Speaker>>() {}.type
    val allSpeakers: ArrayList<Speaker> = gson.fromJson(jsonFileString, listSpeakerType)

    brandsRecView.layoutManager = LinearLayoutManager(this)
    brandsRecView.adapter = SpeakerBrandAdapter(allSpeakers){
        val intent = Intent(this, BrandMenuActivity::class.java)
        intent.putExtra("allSpeakers", allSpeakers)
        intent.putExtra("brand", it)
        startActivity(intent)
    }

}

品牌菜单活动:

    class BrandMenuActivity() : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_brand_menu)

    setSupportActionBar(findViewById(R.id.brandToolbar))
    supportActionBar?.title = intent.getStringExtra("brand")
    supportActionBar?.setDisplayHomeAsUpEnabled(true)

    val brand = intent.getStringExtra("brand")
    val allSpeakers: ArrayList<Speaker> = intent.getParcelableArrayListExtra("allSpeakers")

    brandMenuRecView.layoutManager = LinearLayoutManager(this.applicationContext)
    brandMenuRecView.adapter = BrandMenuAdapter(brand, allSpeakers) {
        val intent = Intent(this, SpeakerDetailActivity::class.java)
        intent.putExtra("speaker", it)
        startActivity(intent)
    }
}

详细信息活动:

    class SpeakerDetailActivity: AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_speaker_detail)

    setSupportActionBar(findViewById(R.id.detailToolbar))
    supportActionBar?.setDisplayHomeAsUpEnabled(true)

    val speaker = intent.getParcelableExtra<Speaker>("speaker")

    val modelImage = findViewById<ImageView>(R.id.imgSpeakerImage)
    val brandText = findViewById<TextView>(R.id.txtBrandName)
    val modelText = findViewById<TextView>(R.id.txtModel)

    brandText.text = speaker.brand
    modelText.text = speaker.model
    val resID = resources.getIdentifier(speaker.imgString, "drawable", packageName)
    modelImage.setImageResource(resID)

    speakerDetailRecView.layoutManager = LinearLayoutManager(this.applicationContext)
    speakerDetailRecView.adapter = SpeakerDetailAdapter(speaker)
}

崩溃时的日志:

    E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.speakerskotlin, PID: 12099
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.speakerskotlin/com.example.speakerskotlin.BrandMenuActivity}: java.lang.IllegalStateException: intent.getParcelableArrayListExtra("allSpeakers") must not be null
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
 Caused by: java.lang.IllegalStateException: intent.getParcelableArrayListExtra("allSpeakers") must not be null
    at com.example.speakerskotlin.BrandMenuActivity.onCreate(BrandMenuActivity.kt:20)
    at android.app.Activity.performCreate(Activity.java:7802)
    at android.app.Activity.performCreate(Activity.java:7791)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7356) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)