在Android的静音流 [英] Muting streams in Android

问题描述

我已经建立了一个小的应用程序使用类 AudioManager 的静音/取消静音的音乐流。 事实上，它的工作，直到我关闭应用程序。即我静音sream，我关闭应用程序，我重新启动应用程序和按钮不会取消静音的流了。我已经搜查了网，但似乎没有人遇到这个问题。

下面是我的code：

 公共类ControlloVolume延伸活动{
切换按钮tb_mute;
按钮btn_mute;
AudioManager mAudioManager;
布尔静音;

@覆盖
公共无效的onCreate（包savedInstanceState）{
    super.onCreate（savedInstanceState）;
    的setContentView（R.layout.activity_controllo_volume）;

    tb_mute =（切换按钮）findViewById（R.id.tb_mute）;
    btn_mute =（按钮）findViewById（R.id.btn_mute）;
    mAudioManager =（AudioManager）getSystemService（Context.AUDIO_SERVICE）;

    如果（mAudioManager.getStreamVolume（AudioManager.STREAM_MUSIC）== 0）{
        静音= TRUE;
        tb_mute.setChecked（静音）;
    }其他{
        静音=假;
        tb_mute.setChecked（静音）;
    }

    }

公共无效onButtonClicked（查看视图）{
    如果（！静音）{
        mAudioManager.setStreamMute（AudioManager.STREAM_MUSIC，真正的）;
        tb_mute.setChecked（真正的）;
        静音= TRUE;
    }其他{
        mAudioManager.setStreamMute（AudioManager.STREAM_MUSIC，假）;
        tb_mute.setChecked（假）;
        静音=假;
    }
}
 

解决方案

首先，要注意的我们不推荐

  

对于一个更好的用户体验，应用程序必须取消静音静音流   在的onPause（），并在适当时在onResume再次静音（）。

不过，我假设你知道你在做什么，所以在这里我们去。

请注意这条线从文档上 setStreamMute

  

静音命令进行保护，防止客户端进程死亡：如果一个   工艺与流活跃静音要求死，这个流将   被自动取消静音。

我检查我的设备上而事实上，当我刚离开我的活动，流保持静音。但只要我杀的过程中，静音消失。 看看活动周期。

由于您目前的做法将不能可靠地工作，你可以写一个前台服务将触发静音 - 开始从活动的服务。 另外你可能会需要 setStreamSolo 。

二重要的东西。

1. 音量== 0 和静音是不一样的事情。即流可以带有音量== 0，但可以没有静音。但如果流的是的静音，音量将始终为0
2. 静音的要求是累积的。即如果你已经设置静音两次，你必须取消静音，以及两倍 - 你的code不处理

作为一个侧面说明，对于这样的应用程序，你可能会想使用的小部件，而不是活动。

---

题外话。这似乎令人惊讶的很多人没有完全得到布尔值是如何工作的。 当我看到code，如你regulary，这里是一个有点流线型重写。

  @覆盖
公共无效的onCreate（包savedInstanceState）{
    // ...设置就像你一样

    //布尔就像任何其他类型的。你不仅可以分配
    //常量，但EX pressions太
    静音=（mAudioManager.getStreamVolume（AudioManager.STREAM_MUSIC）== 0）;
    tb_mute.setChecked（静音）;
}

公共无效onButtonClicked（查看视图）{
    静音=静音！; //反转值
    mAudioManager.setStreamMute（AudioManager.STREAM_MUSIC，静音）;
    tb_mute.setChecked（静音）;
}
 

I've built a small app that mutes/unmute the music stream using the class AudioManager. In fact, it works until I close the application. i.e. I've muted the sream, I close the app, I restart the app and the button doesn't unmute the stream any more. I've searched in the net but no one seems to have met this problem.

Here's my code:

public class ControlloVolume extends Activity {
ToggleButton tb_mute;
Button btn_mute;
AudioManager mAudioManager;
boolean mute;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_controllo_volume);

    tb_mute = (ToggleButton) findViewById(R.id.tb_mute);
    btn_mute = (Button) findViewById(R.id.btn_mute);
    mAudioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);

    if(mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC)==0){
        mute = true;
        tb_mute.setChecked(mute);
    }else{
        mute = false;
        tb_mute.setChecked(mute);
    }

    }

public void onButtonClicked(View view){
    if(!mute){
        mAudioManager.setStreamMute(AudioManager.STREAM_MUSIC, true);
        tb_mute.setChecked(true);
        mute = true;
    }else{
        mAudioManager.setStreamMute(AudioManager.STREAM_MUSIC, false);
        tb_mute.setChecked(false);
        mute = false;
    }
}

解决方案

First, beware it's not recommended

For a better user experience, applications MUST unmute a muted stream in onPause() and mute it again in onResume() if appropriate.

But I assume you know what you're doing, so here we go.

Note this line from the docs on setStreamMute

The mute command is protected against client process death: if a process with an active mute request on a stream dies, this stream will be unmuted automatically.

I've checked on my device and indeed, when I just exit my activity, stream stays muted. But as soon as I kill the process, mute goes away. Take a look at activity lifecycle.

As your current approach will not work reliably, you could write a foreground service which will trigger the mute - start that service from your activity. Also you would likely need to setStreamSolo.

Two important things.

1. Volume==0 and muted are NOT the same thing. I.e. stream can have volume==0 but be not muted. Though if stream is muted, volume will always be 0
2. mute requests are cumulative. I.e. if you've set mute twice, you must unmute twice as well - your code doesn't handle that

As a side note, for such app you would probably want to use widget instead of activity.

---

Off topic. It seems surprisingly lot of people don't quite get how booleans work. And as I see code such as yours regulary, here is a bit streamlined rewrite.

@Override
public void onCreate(Bundle savedInstanceState) {
    // ... setup just like you did

    // boolean is just like any other type. You can assign not only
    // constants, but expressions too
    mute = (mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC)==0);
    tb_mute.setChecked(mute);
}

public void onButtonClicked(View view){
    mute = !mute; // invert value
    mAudioManager.setStreamMute(AudioManager.STREAM_MUSIC, mute);
    tb_mute.setChecked(mute);
}

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