为什么在停止 MediaRecorder 时会出现 IllegalStateException？

Question

为了更好地理解 Android 中的音频录制和播放，我在 android 开发教程 https://developer.android.com/guide/topics/media/mediarecorder#sample-code

中实现了代码的克隆

开始录制时没有出现任何错误，但是，我还没有验证是否真的在进行任何录制。然后当我停止录制时，应用程序崩溃到之前的 activity 并且在随后的尝试中弹出 "app keeps crashing" 对话框并且应用程序退出。

我在 AndroidManifest

中有 <uses-permission android:name="android.permission.RECORD_AUDIO" />

private void onRecord(boolean start) {
        if (start) {
            startRecording();
        } else {
            stopRecording();   // Line 53 //
        }
    }

private void startRecording() {
        recorder = new MediaRecorder();
        recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
        recorder.setOutputFile(fileName);
        System.out.println(fileName);
        recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);

        try {
            recorder.prepare();
        } catch (IOException e) {
            Log.e(LOG_TAG, "prepare() failed");
            //e.printStackTrace();
        }
    }

private void stopRecording() {
        recorder.stop();       // Line 98 //
        recorder.release();
        recorder = null;
    }

class RecordButton extends AppCompatButton {
        boolean mStartRecording = true;

        OnClickListener clicker = new OnClickListener() {
            public void onClick(View v) {
                onRecord(mStartRecording);
                if(mStartRecording) {
                    setText(R.string.stop_recording);
                } else {
                    setText(R.string.start_recording);
                }
                mStartRecording = !mStartRecording;
            }
        };

        public RecordButton(Context ctx){
            super(ctx);
            setText(R.string.start_recording);
            setOnClickListener(clicker);
        }
    }

Logcat 输出：

2020-02-14 10:57:09.789 23619-23619/? E/Zygote: accessInfo : 1
2020-02-14 10:57:09.820 23619-23619/? E/.xxxxxx.xxxxxx: Unknown bits set in runtime_flags: 0x8000
2020-02-14 10:57:12.925 23619-23619/xx.xxxxxxx.xxxxxx.xxxxxxx E/MediaRecorder: stop called in an invalid state: 8
2020-02-14 10:57:12.927 23619-23619/xx.xxxxxxx.xxxxxx.xxxxxxx E/AndroidRuntime: FATAL EXCEPTION: main
    Process: xx.xxxxxxx.xxxxxx.xxxxxxx, PID: 23619
    java.lang.IllegalStateException
        at android.media.MediaRecorder._stop(Native Method)
        at android.media.MediaRecorder.stop(MediaRecorder.java:1440)
        at xx.xxxxxxx.xxxxxx.xxxxxxx.RecordActivity.stopRecording(RecordActivity.java:98)
        at xx.xxxxxxx.xxxxxx.xxxxxxx.RecordActivity.onRecord(RecordActivity.java:53)
        at xx.xxxxxxx.xxxxxx.xxxxxxx.RecordActivity.access[=11=]0(RecordActivity.java:21)
        at xx.xxxxxxx.xxxxxx.xxxxxxx.RecordActivity$RecordButton.onClick(RecordActivity.java:108)
        at android.view.View.performClick(View.java:7866)
        at android.widget.TextView.performClick(TextView.java:14952)
        at android.view.View.performClickInternal(View.java:7839)
        at android.view.View.access00(View.java:886)
        at android.view.View$PerformClick.run(View.java:29363)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:7811)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1076)

如果需要，我可以提供任何相关的附加代码或详细信息

编辑请求权限如下：

    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch (requestCode){
            case REQUEST_RECORD_AUDIO_PERMISSION:
                permissionToRecordAccepted  = grantResults[0] == PackageManager.PERMISSION_GRANTED;
                break;
        }
        if (!permissionToRecordAccepted ) finish();

    }

并在 onCreate() 内部：

ActivityCompat.requestPermissions(this, permissions, REQUEST_RECORD_AUDIO_PERMISSION);

编辑 2 * 我已验证正在创建录音文件，但大小为 0 B

Answer 1

媒体播放器

在下面的 flowchart 中，stop() 有效状态是 {Prepared, Started, Stopped, Paused, PlaybackCompleted}。其他状态（空闲、初始化、错误）是不有效状态，无法调用 stop()。否则，IllegalStateException 抛出。

因此，对于 Ensure，我们应该为 MediaPlayer 设置状态 listeners。因为 Prepared 状态比 setOnPreparedListener 更早初始化 player 我们可以安全地停止播放器。

...
boolean isPrepared = false;
...
recorder.setOnPreparedListener ....
{
...
isPrepared = true;
...
}
...
private void stopRecording() {
    if(isPrepared){
        player.stop();  
        ...
    }
}

为了更好理解，我做了代码总结。

媒体记录器

下面flowchart中，stop()只有在录音状态下才可用。否则，调用 stop() 会抛出 IllegalStateException.

为了安全地停止或释放记录器资源，我们必须确保记录器已经启动。

recorder.start();   // Recording is now started

针对您的特定代码

boolean isRecording = false;
private void startRecording() {
        recorder = new MediaRecorder();
        recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
        recorder.setOutputFile(fileName);
        System.out.println(fileName);
        recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);

        try {
            recorder.prepare();
            recorder.start();
            isRecording = true;
        } catch (IOException e) {
            Log.e(LOG_TAG, "prepare() failed");
            //e.printStackTrace();
        }
}
....
private void stopRecording() {
    if(isRecording){
        recorder.stop();  
    }
    recorder.reset();   // You can reuse the object by going back to setAudioSource() step
    recorder.release(); // Now the object cannot be reused
    isRecording = false;
}

如果我们处于录音状态，停止然后释放它，否则就释放它。

为什么在停止 MediaRecorder 时会出现 IllegalStateException？

Why am I getting an IllegalStateException when stopping MediaRecorder?

java

android

audio-recording

mediarecorder

媒体播放器

媒体记录器