如何深入理解Android播放器的源码结构？

Android播放器源码涉及到的内容较多，这里给出一个简单的示例，使用ExoPlayer库实现一个基本的音频播放器，首先需要在项目的build.gradle文件中添加ExoPlayer依赖：

dependencies {
    implementation 'com.google.android.exoplayer:exoplayer:2.X.X'
}

然后创建一个名为AudioPlayerActivity的Activity，并在布局文件中添加一个播放按钮和一个暂停按钮：

<! activity_audio_player.xml >
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/resauto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".AudioPlayerActivity">
    <Button
        android:id="@+id/play_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Play" />
    <Button
        android:id="@+id/pause_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Pause" />
</LinearLayout>

接下来在AudioPlayerActivity中初始化ExoPlayer并设置播放和暂停按钮的点击事件：

import androidx.appcompat.app.AppCompatActivity;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import com.google.android.exoplayer2.ExoPlayerFactory;
import com.google.android.exoplayer2.SimpleExoPlayer;
import com.google.android.exoplayer2.source.MediaSource;
import com.google.android.exoplayer2.source.ProgressiveMediaSource;
import com.google.android.exoplayer2.trackselection.DefaultTrackSelector;
import com.google.android.exoplayer2.upstream.DefaultDataSourceFactory;
import com.google.android.exoplayer2.util.Util;
import java.io.IOException;
public class AudioPlayerActivity extends AppCompatActivity {
    private SimpleExoPlayer player;
    private boolean playWhenReady = true;
    private int currentWindow = 0;
    private long playbackPosition = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_audio_player);
        findViewById(R.id.play_button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                play();
            }
        });
        findViewById(R.id.pause_button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                pause();
            }
        });
    }
    private void initPlayer() {
        if (player == null) {
            player = ExoPlayerFactory.newSimpleInstance(this, new DefaultTrackSelector());
        }
    }
    private void releasePlayer() {
        if (player != null) {
            player.release();
            player = null;
        }
    }
    private void play() {
        initPlayer();
        player.setPlayWhenReady(true);
    }
    private void pause() {
        if (player != null) {
            player.setPlayWhenReady(false);
        }
    }
    @Override
    protected void onStart() {
        super.onStart();
        if (Util.SDK_INT > 23) {
            initializePlayer();
        }
    }
    @Override
    protected void onResume() {
        super.onResume();
        hideSystemUi();
        if (Util.SDK_INT <= 23 || player == null) {
            initializePlayer();
        }
    }
    @Override
    protected void onPause() {
        super.onPause();
        if (Util.SDK_INT <= 23) {
            releasePlayer();
        }
    }
    @Override
    protected void onStop() {
        super.onStop();
        if (Util.SDK_INT > 23) {
            releasePlayer();
        }
    }
    private void initializePlayer() {
        if (player == null) {
            initPlayer();
        }
        player.seekTo(currentWindow, playbackPosition);
        player.setPlayWhenReady(playWhenReady);
    }
}

代码实现了一个简单的音频播放器，可以播放和暂停音频，要实现更复杂的功能，如播放列表、进度条、音量控制等，可以参考ExoPlayer官方文档和示例。