android - 按下音量调低会延迟调用 onKeyDown(而音量调高会及时调用)

Question

我在一个非常简单的 Activity 中实现了 onKeyDown 和 onKeyUp，并注意到降低音量键有奇怪的行为。

代码如下:

    public boolean onKeyDown(int keyCode, KeyEvent event) 
{
    if ((keyCode == KeyEvent.KEYCODE_VOLUME_DOWN))
    {
        B9=true;
        Log.w("Alon", "Volume_down Down "+SystemClock.elapsedRealtime());
    }
    else if ((keyCode == KeyEvent.KEYCODE_VOLUME_UP))
    {
        B10=true;
        Log.w("Alon", "Volume_up Down "+SystemClock.elapsedRealtime());
    }
    else 
           return super.onKeyDown(keyCode, event);

    return true;
}
public boolean onKeyUp (int keyCode, KeyEvent event) 
{
    if ((keyCode == KeyEvent.KEYCODE_VOLUME_DOWN))
    {
        B9=false;
        Log.w("Alon", "Volume_down Up "+SystemClock.elapsedRealtime());
    }
    else if ((keyCode == KeyEvent.KEYCODE_VOLUME_UP))
    {
        B10=false;
        Log.w("Alon", "Volume_up Up "+SystemClock.elapsedRealtime());
    }
    else 
       return super.onKeyDown(keyCode, event);
    return true;
}

点击音量调高并尽可能快地放手会产生正确的结果:

12-15 17:43:22.215: W/Alon(751): Volume_up Down 74650325
12-15 17:43:22.265: W/Alon(751): Volume_up Up 74650374
12-15 17:43:22.705: W/Alon(751): Volume_up Down 74650818
12-15 17:43:22.765: W/Alon(751): Volume_up Up 74650878
12-15 17:43:23.566: W/Alon(751): Volume_up Down 74651675
12-15 17:43:23.656: W/Alon(751): Volume_up Up 74651768
12-15 17:43:24.107: W/Alon(751): Volume_up Down 74652222
12-15 17:43:24.177: W/Alon(751): Volume_up Up 74652284

对降低音量做同样的事情不会:

12-15 17:44:13.139: W/Alon(751): Volume_down Down 74701252
12-15 17:44:13.139: W/Alon(751): Volume_down Up 74701253
12-15 17:44:13.840: W/Alon(751): Volume_down Down 74701950
12-15 17:44:13.840: W/Alon(751): Volume_down Up 74701950
12-15 17:44:14.751: W/Alon(751): Volume_down Down 74702863
12-15 17:44:14.761: W/Alon(751): Volume_down Up 74702865
12-15 17:44:15.431: W/Alon(751): Volume_down Down 74703546
12-15 17:44:15.431: W/Alon(751): Volume_down Up 74703547
12-15 17:44:16.673: W/Alon(751): Volume_down Down 74704785
12-15 17:44:16.673: W/Alon(751): Volume_down Up 74704785

我在两部手机(Nexus 4 和 Galaxy S)上进行了测试并得到了相同的结果。这是 Android 中的已知问题吗？我做错了什么吗？

Answer 1

VOLUME_DOWN + POWER_KEY 是触发截图的特殊组合键。

当按下 VOLUME_DOWN 键时，事件在 PhoneWindowManager 派发之前被拦截。

PhoneWindowManager 告诉调度员在调度之前稍等(150 毫秒)，以防用户触发屏幕截图……这就是调度员所做的:他等待…… .

...然后 VOLUME_DOWN 键上升。调度程序可以立即调度 VOLUME_DOWN up 事件(即在这种情况下:PhoneWindowManager 没有任何理由告诉调度程序等待)。

但是:队列中有待处理的 VOLUME_DOWN。因此，调度程序在 VOLUME_DOWN 上升之后立即下降 VOLUME_DOWN。

PhoneWindowManager 中的一些代码:

    // If we think we might have a volume down & power key chord on the way
    // but we're not sure, then tell the dispatcher to wait a little while and
    // try again later before dispatching.
    if (mScreenshotChordEnabled && (flags & KeyEvent.FLAG_FALLBACK) == 0) {
        if (mVolumeDownKeyTriggered && !mPowerKeyTriggered) {
            final long now = SystemClock.uptimeMillis();
            final long timeoutTime = mVolumeDownKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS;
            if (now < timeoutTime) {
                return timeoutTime - now;
            }
        }
        if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN
                && mVolumeDownKeyConsumedByScreenshotChord) {
            if (!down) {
                mVolumeDownKeyConsumedByScreenshotChord = false;
            }
            return -1;
        }
    }