Android6.0 源碼修改之屏蔽導航欄虛擬按鍵（Home和RecentAPP）/動態顯示和隱藏NavigationBar

場景分析，
為了完全實現沉浸式效果，在進入特定的app后可以將導航欄移除，當退出app后再次將導航欄恢復。（下面將采用發送廣播的方式來移除和恢復導航欄）

ps：不修改源碼的情況下，簡單的沉浸式效果實現代碼如下，在ACitivy中添加即可（此種做法的缺點是當界面彈出對話框時或者點擊的屏幕的頂部或底部邊緣，會再次出現導航欄和狀態欄）

@Override
public void onWindowFocusChanged(boolean hasFocus) {//new add
    super.onWindowFocusChanged(hasFocus);

    if (hasFocus && Build.VERSION.SDK_INT >= 19) {
        View decorView = getWindow().getDecorView();
        decorView.setSystemUiVisibility(
                //hide title&navigation
                View.SYSTEM_UI_FLAG_FULLSCREEN
                        |View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
                        |View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);
	}
}

一、屏蔽導航欄虛擬按鍵（Home和RecentAPP）

我們先來分析下底部導航欄所處的控件,
所見即所得，既然是虛擬按鍵，必定有相對應的View，要么是xml的布局文件，要么是自定義View，基於此思路，打開AS中的Tools菜單下Android-->Android Device Monitor-->Hierarchy View ,不會用的童鞋可以自己參考這篇Hierarchy View，這里就不再寫了。

我們發現Home按鍵對應的id為 @+id/home, 有了id我們就已經成功的揪出它了，接下來通過搜索命令

grep -nr 命令

通過搜索，我們發現了Home按鍵的 源碼位置

frameworks\base\packages\SystemUI\res\layout-sw600dp\navigation_bar.xml
frameworks\base\packages\SystemUI\res\layout\navigation_bar.xml

     <!--2018-10-13 cczheng set home KeyButton  visibility  invisible-->
        <com.android.systemui.statusbar.policy.KeyButtonView android:id="@+id/home"
            android:layout_width="162dp" android:paddingStart="42dp" android:paddingEnd="42dp"
            android:layout_height="match_parent"
            android:src="@drawable/ic_sysbar_home"
            android:scaleType="centerInside"
            systemui:keyCode="3"
            systemui:keyRepeat="true"
            android:layout_weight="0"
            android:contentDescription="@string/accessibility_home"
            android:visibility="invisible"
            />
      <!--2018-10-13 cczheng set recent KeyButton  visibility  invisible-->
        <com.android.systemui.statusbar.policy.KeyButtonView android:id="@+id/recent_apps"
            android:layout_width="162dp" android:paddingStart="42dp" android:paddingEnd="42dp"
            android:layout_height="match_parent"
            android:src="@drawable/ic_sysbar_recent"
            android:scaleType="centerInside"
            android:layout_weight="0"
            android:contentDescription="@string/accessibility_recent"
            android:visibility="invisible"
            />

此處說下為什么用invisible，而不用gone, 如果使用gone，剩下的按鍵將自動居中，這並不是我們想要的效果，當你以為按照上面的代碼屏蔽后就可以安心的交差了，那你真是too young too simple了。

繼續搜索 R.id.home,我們接下來查找在java代碼中的引用，找到位置

frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java

public View getBackButton() {
    ImageView view = (ImageView) mCurrentView.findViewById(R.id.back);
    view.setImageDrawable(mNavBarPlugin.getBackImage(view.getDrawable()));
    return view;
}

很明顯通過getBackButton()方法能獲取到該View，就能對View進行操作，繼續查看調用getBackButton()的地方

找到當前類中

public void setDisabledFlags(int disabledFlags, boolean force) {
    if (!force && mDisabledFlags == disabledFlags) return;

    mDisabledFlags = disabledFlags;
	...

	getBackButton().setVisibility(disableBack ? View.INVISIBLE : View.VISIBLE);
    getHomeButton().setVisibility(disableHome ? View.INVISIBLE : View.VISIBLE);
    getRecentsButton().setVisibility(disableRecent ? View.INVISIBLE : View.VISIBLE);

    //2018-10-13 cczheng add recent KeyButton  visibility  invisible
    getHomeButton().setVisibility(View.INVISIBLE);  
    getRecentsButton().setVisibility(View.INVISIBLE);
    //2018-10-13 cczheng add recent KeyButton  visibility  invisible

 	 ...
}

另外一處位於
frameworks\base\packages\SystemUI\src\com\android\systemui\statusbar\phone\PhoneStatusBar.java

private void prepareNavigationBarView() {
    mNavigationBarView.reorient();

    mNavigationBarView.getRecentsButton().setOnClickListener(mRecentsClickListener);
    mNavigationBarView.getRecentsButton().setOnTouchListener(mRecentsPreloadOnTouchListener);
    mNavigationBarView.getRecentsButton().setLongClickable(true);
    mNavigationBarView.getRecentsButton().setOnLongClickListener(mLongPressBackRecentsListener);
    mNavigationBarView.getBackButton().setLongClickable(true);
    mNavigationBarView.getBackButton().setOnLongClickListener(mLongPressBackRecentsListener);
    mNavigationBarView.getHomeButton().setOnTouchListener(mHomeActionListener);
    mNavigationBarView.getHomeButton().setOnLongClickListener(mLongPressHomeListener);
    mAssistManager.onConfigurationChanged();

    //2018-10-13 cczheng set recent KeyButton  visibility  invisible
    mNavigationBarView.getHomeButton().setVisibility(View.INVISIBLE);  
    mNavigationBarView.getRecentsButton().setVisibility(View.INVISIBLE);
    //2018-10-13 cczheng set recent KeyButton  visibility  invisible

	....
 }

ok，大功告成，重新mm，編譯替換SystemUI.apk重啟查看效果。

二、動態顯示和隱藏NavigationBar

文章開頭提到將以廣播的方式來實現動態顯示和隱藏NavigationBar這一功能，那么我們改從哪里入手呢？細心的你可能已經發現了上面的一個方法，prepareNavigationBarView()在PhoneStatusBar.java中，從方法名字就能猜到它和NavigationBar的加載有關。查找prepareNavigationBarView()引用

// For small-screen devices (read: phones) that lack hardware navigation buttons
private void addNavigationBar() {
    if (DEBUG) Log.v(TAG, "addNavigationBar: about to add " + mNavigationBarView);
    if (mNavigationBarView == null) return;

    prepareNavigationBarView();

    mWindowManager.addView(mNavigationBarView, getNavigationBarLayoutParams());
}

private void repositionNavigationBar() {
    if (mNavigationBarView == null || !mNavigationBarView.isAttachedToWindow()) return;

    prepareNavigationBarView();

    mWindowManager.updateViewLayout(mNavigationBarView, getNavigationBarLayoutParams());
}

共有兩處引用，很明顯找對地方了，在addNavigationBar()中，核心方法是通過mWindowManager.addView()添加的。看到這你應該明白了，導航欄其實就是一個在window最底部添加的View，既然有addView，對應就有removeView，查找源碼中並未發現提供了removeView方法。看來需要我們自己來實現這個方法。

PS:如果想實現屏蔽整個NavigationBar的效果，可直接將addNavigationBar()方法注釋

@Override
public void start() {
    mDisplay = ((WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE))
            .getDefaultDisplay();
    updateDisplaySize();
    mScrimSrcModeEnabled = mContext.getResources().getBoolean(
            R.bool.config_status_bar_scrim_behind_use_src);

    super.start(); // calls createAndAddWindows()

    mMediaSessionManager
            = (MediaSessionManager) mContext.getSystemService(Context.MEDIA_SESSION_SERVICE);
    // TODO: use MediaSessionManager.SessionListener to hook us up to future updates
    // in session state

    //"anotation this can hide navigationbar" 注釋此處的addNavigationBar即可
    addNavigationBar();

    // Lastly, call to the icon policy to install/update all the icons.
    mIconPolicy = new PhoneStatusBarPolicy(mContext, mCastController, mHotspotController,
            mUserInfoController, mBluetoothController);
    mIconPolicy.setCurrentUserSetup(mUserSetup);
    mSettingsObserver.onChange(false); // set up
}

完整的通過廣播動態顯示和隱藏NavigationBar的代碼如下所示：

////2018-10-13 cczheng hide or show navigationbat by broadcast 
private NotifyChangeNavigationBarBroadcast mNotifyChangeNavigationBarBroadcast;
private static final String SHOW_NAVIGATION = "cc.intent.systemui.shownavigation";
private static final String HIDE_NAVIGATION = "cc.intent.systemui.hidenavigation";


@Override
public void start() {
    mDisplay = ((WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE))
            .getDefaultDisplay();
    updateDisplaySize();
    mScrimSrcModeEnabled = mContext.getResources().getBoolean(
            R.bool.config_status_bar_scrim_behind_use_src);

	....

	//2018-10-13 cczheng hide or show navigationbat by broadcast 
    mNotifyChangeNavigationBarBroadcast = new NotifyChangeNavigationBarBroadcast();
    IntentFilter mfilter = new IntentFilter();
    mfilter.addAction(HIDE_NAVIGATION);
    mfilter.addAction(SHOW_NAVIGATION);
    mContext.registerReceiver(mNotifyChangeNavigationBarBroadcast, mfilter);

}


private void prepareNavigationBarView() {
    mNavigationBarView.reorient();

    mNavigationBarView.getRecentsButton().setOnClickListener(mRecentsClickListener);
    mNavigationBarView.getRecentsButton().setOnTouchListener(mRecentsPreloadOnTouchListener);
    mNavigationBarView.getRecentsButton().setLongClickable(true);
    mNavigationBarView.getRecentsButton().setOnLongClickListener(mLongPressBackRecentsListener);
    mNavigationBarView.getBackButton().setLongClickable(true);
	.....
	//2018-10-13 cczheng hide or show navigationbat by broadcast start
    if (!isNavigationShow) {
        int newVal = mSystemUiVisibility;
        mSystemUiVisibility = View.SYSTEM_UI_FLAG_VISIBLE;
        setSystemUiVisibility(newVal, /*SYSTEM_UI_VISIBILITY_MASK*/Color.TRANSPARENT);
        int hints = mNavigationIconHints;
        mNavigationIconHints = 0;
        setNavigationIconHints(hints);
        topAppWindowChanged(mShowMenu);
    }
    //2018-10-13 cczheng hide or show navigationbat by broadcast end

}

//2018-10-13 cczheng hide or show navigationbat by broadcast start
private static boolean isNavigationShow = true ;
class NotifyChangeNavigationBarBroadcast extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        Log.i(TAG, "NotifyChangeNavigationBarBroadcast: action =" + action); 
        if (HIDE_NAVIGATION.equals(action)) {
            isNavigationShow = false;
            hideNavigationBar();
        }else if (SHOW_NAVIGATION.equals(action)) {
            if (isNavigationShow) return;

            showNavigationBar();
        }
    }
};

private void showNavigationBar() {
    mNavigationBarView =(NavigationBarView) View.inflate(mContext, R.layout.navigation_bar, null);
    mNavigationBarView.setBar(this);
    
    addNavigationBar();
    isNavigationShow = true;

    // mNavigationBarView.setBackgroundColor(Color.TRANSPARENT);
}

private void hideNavigationBar() {
    Log.d(TAG, "hideNavigationBar: about to remove"  + mNavigationBarView);
    if (mNavigationBarView == null) return;

    mWindowManager.removeView(mNavigationBarView);
    mNavigationBarView = null;
}
//2018-10-13 cczheng hide or show navigationbat by broadcast end

ok, 動態顯示和隱藏NavigationBar的功能也搞定了。

三、總結

Hierarchy View是一個非常好用的利器，不僅是對源碼分析查找，當你要查看借鑒別人的app時也會是一個非常好用的扳手。So，多研究研究吧。

下一篇將介紹在不修改源碼的情況下，通過兩種方式實現加載loading對話框的功能(不退出沉浸式效果)

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