首先，按下按鍵后會(huì)走到PhoneWindowManager中。

//frameworks\base\services\core\java\com\android\server\policy\PhoneWindowManager.java
public class PhoneWindowManager implements WindowManagerPolicy {
    /** {@inheritDoc} */
    @Override
    public long interceptKeyBeforeDispatching(WindowState win, KeyEvent event, int policyFlags) {
.........
else if (keyCode == KeyEvent.KEYCODE_VOLUME_UP
                || keyCode == KeyEvent.KEYCODE_VOLUME_DOWN
                || keyCode == KeyEvent.KEYCODE_VOLUME_MUTE) {
            if (mUseTvRouting || mHandleVolumeKeysInWM) {
                // On TVs or when the configuration is enabled, volume keys never
                // go to the foreground app.
                dispatchDirectAudioEvent(event);
                return -1;
            }
.........
        // Let the application handle the key.
        return 0;
    }

這里并沒(méi)有調(diào)用dispatchDirectAudioEvent，由于mUseTvRouting 和mHandleVolumeKeysInWM都為false，所以會(huì)繼續(xù)向下分發(fā)。有System UI中有定義VolumeDialogImpl，按下音量調(diào)節(jié)后會(huì)音量條視圖彈出。
如下所示。

https://blog.csdn.net/qq_25094789/article/details/90237770?depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-3&utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-3

VolumeDialogImpl中調(diào)節(jié)音量（無(wú)論是增加還是減少）是調(diào)用updateVolumeRowH，vlevel是音量，因此新增代碼是以vlevel為0為判斷條件，發(fā)送廣播。

//vendor\mediatek\proprietary\packages\apps\SystemUI\src\com\android\systemui\volume\VolumeDialogImpl.java
public class VolumeDialogImpl implements VolumeDialog, TunerService.Tunable {
     .........................

    private void updateVolumeRowH(VolumeRow row) {
        Log.i(TAG, "updateVolumeRowH s=" + row.stream);
     .........................
        // update slider
        final boolean enableSlider = !zenMuted;
        final int vlevel = row.ss.muted && (!isRingStream && !zenMuted) ? 0
                : row.ss.level;
        updateVolumeRowSliderH(row, enableSlider, vlevel);

        if(vlevel == 0){
            Intent intent = new Intent();
            intent.setAction("android.media.silent");
            mContext.sendBroadcast(intent);
        }else {
            Intent intent = new Intent();
            intent.setAction("android.media.normal");
            mContext.sendBroadcast(intent);
        }
    }

根據(jù)Android N SystemUI－狀態(tài)欄可知，狀態(tài)欄的圖標(biāo)是分成通知圖標(biāo)和系統(tǒng)圖標(biāo)的。添加靜音圖標(biāo)算是系統(tǒng)圖標(biāo)的添加。

PhoneStatusBarPolicy處理status bar的圖標(biāo)的顯示,因此需要添加2個(gè)地方1.addAction 2.mIconController.setIconVisibility
具體修改如下。

//vendor\mediatek\proprietary\packages\apps\SystemUI\src\com\android\systemui\statusbar\phone\PhoneStatusBarPolicy.java
public class PhoneStatusBarPolicy implements Callback, Callbacks,
        RotationLockControllerCallback, Listener, LocationChangeCallback,
        ZenModeController.Callback, DeviceProvisionedListener, KeyguardMonitor.Callback {
            .........................
    @VisibleForTesting
    public PhoneStatusBarPolicy(Context context, StatusBarIconController iconController) {
        mContext = context;
        mIconController = iconController;
        ......................... 
         filter.addAction(AudioManager.RINGER_MODE_CHANGED_ACTION);                        
        .........................
        filter.addAction("android.media.silent");
        filter.addAction("android.media.normal");
            .........................
     }


    @VisibleForTesting
    /*private*/ BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (action.equals(AudioManager.RINGER_MODE_CHANGED_ACTION) ||
                    action.equals(AudioManager.INTERNAL_RINGER_MODE_CHANGED_ACTION)) {
                updateVolumeZen();
            }else if (action.equals("android.media.silent")){
                mIconController.setIcon(mSlotVolume, R.drawable.stat_sys_ringer_silent, null);
                mIconController.setIconVisibility(mSlotVolume, true);
            }else if (action.equals("android.media.normal")){
                mIconController.setIconVisibility(mSlotVolume, false);
            }
            .........................
    }
}

關(guān)于Slot，可以簡(jiǎn)單參考下面的文章。
vue 里面的slot屬性

這里注意要用stat_sys_ringer_silent這個(gè)stat開(kāi)頭的圖標(biāo)，不然顯示出來(lái)，跟其他圖標(biāo)不協(xié)調(diào)。
顏色控制部分在StatusBarIconController中，涉及到xfermode的使用，具體就不展開(kāi)分析了。

//vendor\mediatek\proprietary\packages\apps\SystemUI\src\com\android\systemui\statusbar\phone\StatusBarIconController.java
        public void setTint(int color) {
            mColor = color;
            for (int i = 0; i < mGroup.getChildCount(); i++) {
                View child = mGroup.getChildAt(i);
                if (child instanceof StatusBarIconView) {
                    StatusBarIconView icon = (StatusBarIconView) child;
                    icon.setStaticDrawableColor(mColor);
                }
            }
        }

參考鏈接：
SystemUI 狀態(tài)欄 system icon 和 notification icon 的修改
狀態(tài)欄 添加 system icon
SystemUI源碼分析三(StatusBar的加載流程)
Android 8.0 SystemUI（三）：一說(shuō)頂部 StatusBar
android(cm11)狀態(tài)欄源代碼分析（一）
android 7.0 system UI之快速啟動(dòng)欄的分析（一）
Android N SystemUI－狀態(tài)欄

Android 修改系統(tǒng)音量條UI

xfermode的基本用法
Android-使用 SetColorFilter 神奇地改變圖片的顏色