android - 为什么连接到mediaBrowser时未调用connectionCallback.onConnected()？

Question

我只是想教自己关于Android音频开发的知识，而对于为什么在这里既不调用connectionCallback的onConnected方法也不对onConnectionFailed方法感到困惑。实例化PodcastService并调用其onGetRoot方法，但不调用回调。没有给出错误信息；根本不调用回调。任何帮助将是巨大的!
MainActivity.kt:

package com.davidwillett.audioapp

import android.content.ComponentName
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.support.v4.media.MediaBrowserCompat

class MainActivity : AppCompatActivity() {
    private val connectionCallback = object : MediaBrowserCompat.ConnectionCallback() {
        override fun onConnected() {
            println("ConnectionCallback.onConnected")
            super.onConnected()
        }

        override fun onConnectionFailed() {
            println("ConnectionCallback.onConnectionFailed")
            super.onConnectionFailed()
        }
    }

    private lateinit var mediaBrowser: MediaBrowserCompat

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

        mediaBrowser = MediaBrowserCompat(
            this,
            ComponentName(this, PodcastService::class.java),
            connectionCallback,
            null)
    }

    override fun onStart() {
        println("MainActivity.onStart")
        super.onStart()
        mediaBrowser.connect()
    }

    override fun onStop() {
        println("MainActivity.onStop")
        super.onStop()
        mediaBrowser.disconnect()
    }
}

PodcastService.kt:

package com.davidwillett.audioapp

import android.os.Bundle
import android.support.v4.media.MediaBrowserCompat
import androidx.media.MediaBrowserServiceCompat

class PodcastService : MediaBrowserServiceCompat() {
    override fun onGetRoot(
        clientPackageName: String,
        clientUid: Int,
        rootHints: Bundle?
    ): BrowserRoot? {
        println("PodcastService.onGetRoot")
        return BrowserRoot("root", null)
    }

    override fun onLoadChildren(
        parentId: String,
        result: Result<MutableList<MediaBrowserCompat.MediaItem>>
    ) {
        TODO("Not yet implemented")
    }
}

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.davidwillett.audioapp">

    <application
        android:allowBackup="false"
        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=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service android:name=".PodcastService"
            android:exported="false">
            <intent-filter>
                <action android:name="android.media.browse.MediaBrowserService" />
            </intent-filter>
        </service>
    </application>

</manifest>

Answer 1

抱歉，我的研究不够好!
UAMP演示项目中的注释指出:“为了调用MediaBrowserCompat.ConnectionCallback.onConnected，需要在MediaBrowserServiceCompat上设置MediaSessionCompat.Token。”
因此，这将是所缺少的!