java - Android - 无法在启动屏幕上播放歌曲

Question

我试图在启动屏幕打开时发出声音，但 Song.start() 返回空指针异常。为什么会出现这种情况呢？我使用的是最小 API 11。

代码:

public class Splash extends Activity{

MediaPlayer song;
@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.bg);

    song = MediaPlayer.create(Splash.this, R.raw.splashmusic);
    song.start();
    Thread timer = new Thread(){//create thread to execute one class to another class within a time
        public void run(){
            try{
                sleep(5000);//5 seconds of pausing
            } catch (InterruptedException e){
                e.printStackTrace();
            }finally{
                Intent openMain = new Intent("com.example.hapshare.DashboardActivity"); 
                startActivity(openMain);
            }
        }
    };
    timer.start();
}

@Override
protected void onPause() {
    // TODO Auto-generated method stub
    super.onPause();
    song.release();
    finish();
}

日志猫:

11-19 09:42:02.631: E/AndroidRuntime(20289): FATAL EXCEPTION: main
11-19 09:42:02.631: E/AndroidRuntime(20289): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.hapshare/com.example.hapshare.Splash}: java.lang.NullPointerException
11-19 09:42:02.631: E/AndroidRuntime(20289):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2517)
11-19 09:42:02.631: E/AndroidRuntime(20289):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2574)
11-19 09:42:02.631: E/AndroidRuntime(20289):    at android.app.ActivityThread.access$600(ActivityThread.java:162)
11-19 09:42:02.631: E/AndroidRuntime(20289):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1413)
11-19 09:42:02.631: E/AndroidRuntime(20289):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-19 09:42:02.631: E/AndroidRuntime(20289):    at android.os.Looper.loop(Looper.java:158)
11-19 09:42:02.631: E/AndroidRuntime(20289):    at android.app.ActivityThread.main(ActivityThread.java:5789)
11-19 09:42:02.631: E/AndroidRuntime(20289):    at java.lang.reflect.Method.invokeNative(Native Method)

Answer 1

看起来您的 MediaPlayer 未正确创建(来自 MediaPlayer create() 的文档):

Returns a MediaPlayer object, or null if creation failed

所以检查一下你的 R.raw.splashmusic

再次来自文档:

In this case, a "raw" resource is a file that the system does not try to parse in any particular way. However, the content of this resource should not be raw audio. It should be a properly encoded and formatted media file in one of the supported formats.

您还可以通过这种方式创建 MediaPlayer 对象:

try {
    AssetFileDescriptor afd = this.getResources().openRawResourceFd(R.raw.splashmusic);

    song = new MediaPlayer();
    song.reset();
    song.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getDeclaredLength());
    song.setAudioStreamType(AudioManager.STREAM_MUSIC);
    song.prepare(); // might take long! (for buffering, etc)

    song.start();
} catch (IllegalStateException e) {
    e.printStackTrace();

} catch (IOException e) {
    e.printStackTrace(); 
}

但请记住，prepare() 可能需要很长时间，因此在 UI 线程上创建 MediaPlayer 并不是一个好主意。您这里有 2 个选择:

• 创建另一个线程并在那里生成 MP
• 使用prepareAsync()，准备完成后，调用通过setOnPreparedListener()配置的MediaPlayer.OnPreparedListener的onPrepared()方法。

请阅读有关 MediaPlayer 的更多信息 here

此外，在创建 Intent 时，而不是:

Intent openMain = new Intent("com.example.hapshare.DashboardActivity"); 

这样做:

Intent openMain = new Intent(this, DashboardActivity.class);