java在Android TTS中没有声音错误的上下文？

Question

我有一个类DistanceAnnouncer，它使用Android文本到语音引擎来宣布两个位置之间的距离。它的构造如下：

public class DistanceAnnouncer {
    private TextToSpeech speaker;

    public DistanceAnnouncer(Context context) {
        speaker = new TextToSpeech(context, new TextToSpeech.OnInitListener() { 
        ...

通过以下方法向用户传达距离：

public void speak(Location targetLocation, Location currentLocation) {
   float distanceInMeters = targetLocation.distanceTo(currentLocation);
   speaker.speak(String.valueOf(distanceInMeters) + " meters",TextToSpeech.QUEUE_FLUSH,null);

在我的MainActivity中，我创建了一个类级对象

protected void onCreate(Bundle savedInstanceState) {

    distanceAnnouncer = new DistanceAnnouncer(this);

单击对话框按钮时，将在匿名方法中使用，如下所示。这个很好用。但现在我想重构代码以使用更少的内存，并想去掉类级变量。为了测试它，我创建了一个新的测试对象，并将其MainActivity.this作为上下文（与构造函数中接收this的类级对象相反）。旧对象仍然有效，新对象则无效。没有抛出异常。代码被执行，但没有声音

代码：

    public void NewTargetButtonClicked(View view) {
        final EditText entryEditText = new EditText(this);

        AlertDialog.Builder alert = new AlertDialog.Builder(this);
        alert.setTitle(R.string.enter_coordinates_prompt);
        alert.setView(entryEditText);
        alert.setCancelable(true);
        alert.setPositiveButton(R.string.ok_button_text, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                if (entryEditText.getText() == null) return;

                Location newLocation = getLocationFromCoords(entryEditText.getText().toString());
                //pagaidām protam apstrādāt tikai decimālgrādus
                if (!(newLocation == null)) {
                    mTargetLocation = newLocation;
                    refreshDistance();
                    Button targetButton = (Button) MainActivity.this.findViewById(R.id.newTargetButton);
                    targetButton.setText(R.string.set_new_target);

                    DistanceAnnouncer newDistanceAnnouncer = new DistanceAnnouncer(MainActivity.this);
                    //THIS DOESN'T WORK:                    
                    newDistanceAnnouncer.speak(mTargetLocation,mCurrentLocation);

                    //THIS WORKS:
                    distanceAnnouncer.speak(mTargetLocation,mCurrentLocation);

                    CheckBox speakCheckbox = (CheckBox) MainActivity.this.findViewById(R.id.speakDistanceCheckbox);
                    speakCheckbox.setVisibility(View.VISIBLE);
                }
            }
        });
        AlertDialog alertDialog = alert.create();

        alertDialog.show();
    }

我怀疑这是语境问题，但在这种情况下，两种语境之间的区别是什么？它们应该是一样的，不是吗

编辑：全距离播音员课程代码：

package com.blueit.audioguide;

import 安卓.app.Activity;
import 安卓.content.Context;
import 安卓.location.Location;
import 安卓.speech.tts.TextToSpeech;

import java.util.Locale;

/**
 * Created by janeks on 23.04.2016..
 */
public class DistanceAnnouncer {
    private TextToSpeech speaker;

    public DistanceAnnouncer(Context context) {
        speaker = new TextToSpeech(context, new TextToSpeech.OnInitListener() {
            @Override
            public void onInit(int status) {
                if(status != TextToSpeech.ERROR) {
                    speaker.setLanguage(Locale.ENGLISH);
                }
            }
        });
    }

    public void speak(Location targetLocation, Location currentLocation) {
        if (targetLocation == null) return;
        if (currentLocation == null) return;

        if ((!(targetLocation == null)) && (!(currentLocation == null))) {
            float distanceInMeters = targetLocation.distanceTo(currentLocation);
            if (distanceInMeters < 1000) {
                distanceInMeters = Math.round(distanceInMeters);
                speaker.speak(String.valueOf(distanceInMeters) + " meters",TextToSpeech.QUEUE_FLUSH,null);
            } else if ((distanceInMeters >= 1000) && (distanceInMeters <= 100000)) {
                float distanceInKilometers = distanceInMeters / 1000;
                distanceInKilometers = Math.round(distanceInKilometers * 10) / 10;
                speaker.speak(String.valueOf(distanceInKilometers) + " kilometers",TextToSpeech.QUEUE_FLUSH,null);
            }  else if (distanceInMeters > 100000) {
                float distanceInKilometers = distanceInMeters / 1000;
                distanceInKilometers = Math.round(distanceInKilometers);
                speaker.speak(String.valueOf(distanceInKilometers) + " kilometers",TextToSpeech.QUEUE_FLUSH,null);
            }
        } else {

        }
    }
}

编辑2：应用程序日志，通过TextToSpeech过滤：

04-23 16:00:03.911 30815-30815/com.blueit.audioguide I/TextToSpeech: Sucessfully bound to com.google.安卓.tts
04-23 16:00:03.988 30815-30815/com.blueit.audioguide I/TextToSpeech: Connected to ComponentInfo{com.google.安卓.tts/com.google.安卓.tts.service.GoogleTTSService}
04-23 16:00:03.995 30815-30932/com.blueit.audioguide I/TextToSpeech: Set up connection to ComponentInfo{com.google.安卓.tts/com.google.安卓.tts.service.GoogleTTSService}
04-23 16:01:35.048 30815-30815/com.blueit.audioguide I/TextToSpeech: Sucessfully bound to com.google.安卓.tts
04-23 16:01:44.346 30815-30815/com.blueit.audioguide W/TextToSpeech: speak failed: not bound to TTS engine

似乎系统将第一个连接到系统TTS服务，但没有连接第二个。但原因是什么？我还尝试删除第一个，只留下第二个（可能每个活动不允许有几个TTS？），但没有成功

Answer 1

只需将一个DistanceAnnouncer实例作为MainActivity的成员变量

总是在AlertDialog中创建一个新实例的问题是TTS引擎不能立即可用。现在你打电话给

DistanceAnnouncer newDistanceAnnouncer = new DistanceAnnouncer(MainActivity.this);

//THIS DOESN'T WORK:                    
newDistanceAnnouncer.speak(mTargetLocation,mCurrentLocation);

。。。然后在正确初始化之前，即在onInit()运行之前，尝试通过TTS引擎说话