为什么在停止MediaRecorder时会收到IllegalStateException？

Question

[为了更好地理解Android中的音频记录和播放，我在android dev教程https://developer.android.com/guide/topics/media/mediarecorder#sample-code中实现了代码的克隆。>

开始录制时没有错误，但是，我还没有验证是否正在实际进行录制。然后，当我停止录制时，应用程序崩溃到上一个活动，并且在随后的尝试中，“应用程序崩溃”对话框弹出，并且该应用程序退出。

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$000(RecordActivity.java:21)
        at xx.xxxxxxx.xxxxxx.xxxxxxx.RecordActivity$RecordButton$1.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.access$3600(View.java:886)
        at android.view.View$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，我可以提供任何其他相关代码或详细信息

编辑请求具有以下权限：

    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();

    }
和onCreate（）内：

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

[为了更好地理解Android中的音频录制和播放，我在android dev教程https：//developer.android.com/guide/topics/media / ...中实现了代码的克隆。

Answer 1

媒体播放器

在下面的flowchart中，stop()的有效状态是{Prepared, Started, Stopped, Paused, PlaybackCompleted}。其他状态（空闲，初始化，错误）是NOT