android中使用MediaRecoder录制声音

package com.test.mediarecorder;

import java.io.File;

import android.media.MediaRecorder;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity implements OnClickListener {

    private Button start, stop;
    private MediaRecorder recorder;
    private File soundFile;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        start = (Button) findViewById(R.id.start);
        stop = (Button) findViewById(R.id.stop);
        
        start.setOnClickListener(this);
        stop.setOnClickListener(this);
        recorder = new MediaRecorder();
        System.out.println(Environment.getExternalStorageDirectory());
    }

    @Override
    public void onClick(View v) {

      try {
          
          switch (v.getId()) {
        case R.id.start:
            if (!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                Toast.makeText(this, "SD not exists", Toast.LENGTH_LONG).show();
                return;
            } 
            // create file to save sound
            soundFile = new File(Environment.getExternalStorageDirectory().getCanonicalFile() + "/sound.amr");
            // set the sound source
            recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
            // set the sound output type it must before set sound encoding
            recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
            //set sound encoding
            recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
            recorder.setOutputFile(soundFile.getAbsolutePath());
            recorder.prepare();
            // start record sound
            recorder.start();
            break;
        case R.id.stop:
            if (soundFile != null && soundFile.exists()) {
                // stop record
                recorder.stop();
                recorder.release();
                recorder = null;
            }
            break;
        }
      }catch (Exception e) {
          e.printStackTrace();
      }
        
    }

}