android - 第一次单击时，Android App不会录制声音

Question

因此，我有一个基于此wesbite中的代码的外观非常酷的Spartan应用程序

这样做的目的是，当用户单击“录制”按钮时，它将提示他或她输入文件名，然后录制声音。用户可以录制任意数量的声音，直到返回主菜单。

但是，当我第一次启动该程序时，单击“录制”按钮将不会发生任何事情。当我第二次点击它时，它将在名称提示下开始记录。

这是什么问题？在代码中，我怀疑问题是我将保存文件名的字符串变量初始化为null，但是在用户单击“取消”的情况下这样做了，因此程序不会将声音记录到名为null的声音文件中。用户在首次尝试启动程序时给它起了一个名字，是否不可以通过null检查？

另外，根据我的代码，程序是否不应该等到名称设置好后再启动记录器？

编码:

import java.io.IOException;


import android.media.MediaRecorder;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.app.ActionBar;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class RecordASound extends Activity {


    Button start;
    Button stop;
    Button mainMenu;
    private MediaRecorder myRecorder;
    private String outputFile = null;
    private String value = null;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_record_asound);



        start = (Button)findViewById(R.id.Record);
        start.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                startRecord(v);
            }
          });

          stop = (Button)findViewById(R.id.StopRecord);
          stop.setEnabled(false);
          stop.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                stopRecord(v);
            }
          });

          mainMenu = (Button)findViewById(R.id.MainMenu);
          mainMenu.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                    mainMenu(v);    
            }
          });


        // Make sure we're running on Honeycomb or higher to use ActionBar APIs
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            // For the main activity, make sure the app icon in the action bar
            // does not behave as a button
            ActionBar actionBar = getActionBar();
            actionBar.setHomeButtonEnabled(false);
        }//end if

    }//end onCreate

    public void startRecord(View view){

        AlertDialog.Builder alert = new AlertDialog.Builder(this);

        alert.setTitle("Name of Sound File");
        alert.setMessage("Please give your sound file a name.");

        // Set an EditText view to get user input 
        final EditText input = new EditText(this);
        alert.setView(input);

        alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int whichButton) {
         value = input.getText().toString();

          }
        });

        alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
          public void onClick(DialogInterface dialog, int whichButton) {
              value = null;

          }
        });

        alert.show();

            //if the user hit cancel on the prompt, back out of the recorder
        if (value == null){
            return;
        }//end if
        else{
            outputFile = Environment.getExternalStorageDirectory().
                    getAbsolutePath() + "/" +  value + ".3gpp";

            myRecorder = new MediaRecorder();
            myRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
            myRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
            myRecorder.setAudioEncoder(MediaRecorder.OutputFormat.AMR_NB);
            myRecorder.setOutputFile(outputFile);


            try {
                  myRecorder.prepare();
                  myRecorder.start();
         } catch (IllegalStateException e) {
                  // start:it is called before prepare()
                  // prepare: it is called after start() or before setOutputFormat()
                          e.printStackTrace();
                     } catch (IOException e) {
             // prepare() fails
                   e.printStackTrace();
                }

               start.setEnabled(false);
               stop.setEnabled(true);

               Toast.makeText(getApplicationContext(), "Start recording...",
                               Toast.LENGTH_SHORT).show();

        }//end else



    }//end startRecord

    public void stopRecord(View view){
        try { // TODO Auto-generated method stub
            myRecorder.stop();
            myRecorder.release();

            myRecorder = null;

            stop.setEnabled(false);
            start.setEnabled(true);

            Toast.makeText(getApplicationContext(), "Stop recording...",
                    Toast.LENGTH_SHORT).show();
        } catch (IllegalStateException e) {

            e.printStackTrace();
        } catch (RuntimeException e){
            //no valid audio/video data was collected
            e.printStackTrace();

        }//end catch

    }//end stopRecord

    public void mainMenu(View view){

        startActivity(new Intent(RecordASound.this, MainActivity.class));

    }//end mainMenu 


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.record_asound, menu);
        return true;
    }//end onCreateOptionsMenu

}//end class

Answer 1

将AlertDialog显示为Android中的对话框是异步的后，将代码放在setPositiveButton中，而不要进行检查。