android4.2导航键显示位置

@Override
    public void beginLayoutLw(boolean isDefaultDisplay, int displayWidth, int displayHeight,
                              int displayRotation) {
        mUnrestrictedScreenLeft = mUnrestrictedScreenTop = 0;
        mUnrestrictedScreenWidth = displayWidth;
        mUnrestrictedScreenHeight = displayHeight;
        mRestrictedScreenLeft = mRestrictedScreenTop = 0;
        mRestrictedScreenWidth = displayWidth;
        mRestrictedScreenHeight = displayHeight;
        mDockLeft = mContentLeft = mStableLeft = mStableFullscreenLeft
                = mSystemLeft = mCurLeft = 0;
        mDockTop = mContentTop = mStableTop = mStableFullscreenTop
                = mSystemTop = mCurTop = 0;
        mDockRight = mContentRight = mStableRight = mStableFullscreenRight
                = mSystemRight = mCurRight = displayWidth;
        mDockBottom = mContentBottom = mStableBottom = mStableFullscreenBottom
                = mSystemBottom = mCurBottom = displayHeight;
        mDockLayer = 0x10000000;
        mStatusBarLayer = -1;
        // start with the current dock rect, which will be (0,0,displayWidth,displayHeight)
        final Rect pf = mTmpParentFrame;
        final Rect df = mTmpDisplayFrame;
        final Rect vf = mTmpVisibleFrame;
        pf.left = df.left = vf.left = mDockLeft;
        pf.top = df.top = vf.top = mDockTop;
        pf.right = df.right = vf.right = mDockRight;
        pf.bottom = df.bottom = vf.bottom = mDockBottom;
        if (isDefaultDisplay) {
            // For purposes of putting out fake window up to steal focus, we will
            // drive nav being hidden only by whether it is requested.
            boolean navVisible = (mLastSystemUiFlags&View.SYSTEM_UI_FLAG_HIDE_NAVIGATION) == 0;
            // When the navigation bar isn't visible, we put up a fake
            // input window to catch all touch events.  This way we can
            // detect when the user presses anywhere to bring back the nav
            // bar and ensure the application doesn't see the event.
            if (navVisible) {
                if (mHideNavFakeWindow != null) {
                    mHideNavFakeWindow.dismiss();
                    mHideNavFakeWindow = null;
                }
            } else if (mHideNavFakeWindow == null) {
                mHideNavFakeWindow = mWindowManagerFuncs.addFakeWindow(
                        mHandler.getLooper(), mHideNavInputEventReceiverFactory,
                        "hidden nav", WindowManager.LayoutParams.TYPE_HIDDEN_NAV_CONSUMER,
                        0, false, false, true);
            }
            // For purposes of positioning and showing the nav bar, if we have
            // decided that it can't be hidden (because of the screen aspect ratio),
            // then take that into account.
            navVisible |= !mCanHideNavigationBar;
            if (mFocusedWindow != null) {
                final int fl = mFocusedWindow.getAttrs().flags;
                if ((fl & View.SYSTEM_UI_FLAG_SHOW_FULLSCREEN) != 0) {
                    navVisible = false;
                }
            }
            if (mNavigationBar != null && ((mLastSystemUiFlags & View.SYSTEM_UI_FLAG_SHOW_FULLSCREEN) == 0)) {
                // Force the navigation bar to its appropriate place and
                // size.  We need to do this directly, instead of relying on
                // it to bubble up from the nav bar, because this needs to
                // change atomically with screen rotations.
                mNavigationBarOnBottom = (!mNavigationBarCanMove || displayWidth < displayHeight);//关键位置
                if (mNavigationBarOnBottom) {
                    // It's a system nav bar or a portrait screen; nav bar goes on bottom.
                    int top = displayHeight - mNavigationBarHeightForRotation[displayRotation];
                    mTmpNavigationFrame.set(0, top, displayWidth, displayHeight);
                    mStableBottom = mStableFullscreenBottom = mTmpNavigationFrame.top;
                    if (navVisible) {
                        mNavigationBar.showLw(true);
                        mDockBottom = mTmpNavigationFrame.top;
                        mRestrictedScreenHeight = mDockBottom - mDockTop;
                    } else {
                        // We currently want to hide the navigation UI.
                        mNavigationBar.hideLw(true);
                    }
                    if (navVisible && !mNavigationBar.isAnimatingLw()) {
                        // If the nav bar is currently requested to be visible,
                        // and not in the process of animating on or off, then
                        // we can tell the app that it is covered by it.
                        mSystemBottom = mTmpNavigationFrame.top;
                    }
                } else {
                    // Landscape screen; nav bar goes to the right.
                    int left = displayWidth - mNavigationBarWidthForRotation[displayRotation];
                    mTmpNavigationFrame.set(left, 0, displayWidth, displayHeight);
                    mStableRight = mStableFullscreenRight = mTmpNavigationFrame.left;
                    if (navVisible) {
                        mNavigationBar.showLw(true);
                        mDockRight = mTmpNavigationFrame.left;
                        mRestrictedScreenWidth = mDockRight - mDockLeft;
                    } else {
                        // We currently want to hide the navigation UI.
                        mNavigationBar.hideLw(true);
                    }
                    if (navVisible && !mNavigationBar.isAnimatingLw()) {
                        // If the nav bar is currently requested to be visible,
                        // and not in the process of animating on or off, then
                        // we can tell the app that it is covered by it.
                        mSystemRight = mTmpNavigationFrame.left;
                    }
                }
                // Make sure the content and current rectangles are updated to
                // account for the restrictions from the navigation bar.
                mContentTop = mCurTop = mDockTop;
                mContentBottom = mCurBottom = mDockBottom;
                mContentLeft = mCurLeft = mDockLeft;
                mContentRight = mCurRight = mDockRight;
                mStatusBarLayer = mNavigationBar.getSurfaceLayer();
                // And compute the final frame.
                mNavigationBar.computeFrameLw(mTmpNavigationFrame, mTmpNavigationFrame,
                        mTmpNavigationFrame, mTmpNavigationFrame);
                if (DEBUG_LAYOUT || true) Log.i(TAG, "mNavigationBar frame: " + mTmpNavigationFrame);
            }
            if (DEBUG_LAYOUT) Log.i(TAG, String.format("mDock rect: (%d,%d - %d,%d)",
                    mDockLeft, mDockTop, mDockRight, mDockBottom));
            // decide where the status bar goes ahead of time
            if (mStatusBar != null) {
                // apply any navigation bar insets
                pf.left = df.left = mUnrestrictedScreenLeft;
                pf.top = df.top = mUnrestrictedScreenTop;
                pf.right = df.right = mUnrestrictedScreenWidth - mUnrestrictedScreenLeft;
                pf.bottom = df.bottom = mUnrestrictedScreenHeight - mUnrestrictedScreenTop;
                vf.left = mStableLeft;
                vf.top = mStableTop;
                vf.right = mStableRight;
                vf.bottom = mStableBottom;
                mStatusBarLayer = mStatusBar.getSurfaceLayer();
                // Let the status bar determine its size.
                mStatusBar.computeFrameLw(pf, df, vf, vf);
                // For layout, the status bar is always at the top with our fixed height.
                mStableTop = mUnrestrictedScreenTop + mStatusBarHeight;
                // If the status bar is hidden, we don't want to cause
                // windows behind it to scroll.
                if (mStatusBar.isVisibleLw()) {
                    // Status bar may go away, so the screen area it occupies
                    // is available to apps but just covering them when the
                    // status bar is visible.
                    mDockTop = mUnrestrictedScreenTop + mStatusBarHeight;
                    mContentTop = mCurTop = mDockTop;
                    mContentBottom = mCurBottom = mDockBottom;
                    mContentLeft = mCurLeft = mDockLeft;
                    mContentRight = mCurRight = mDockRight;
                    if (DEBUG_LAYOUT) Log.v(TAG, "Status bar: " +
                        String.format(
                            "dock=[%d,%d][%d,%d] content=[%d,%d][%d,%d] cur=[%d,%d][%d,%d]",
                            mDockLeft, mDockTop, mDockRight, mDockBottom,
                            mContentLeft, mContentTop, mContentRight, mContentBottom,
                            mCurLeft, mCurTop, mCurRight, mCurBottom));
                }
                if (mStatusBar.isVisibleLw() && !mStatusBar.isAnimatingLw()) {
                    // If the status bar is currently requested to be visible,
                    // and not in the process of animating on or off, then
                    // we can tell the app that it is covered by it.
                    mSystemTop = mUnrestrictedScreenTop + mStatusBarHeight;
                }
            }
        }
    }

public void setInitialDisplaySize(Display display, int width, int height, int density) {
        mDisplay = display;
        int shortSize, longSize;
        if (width > height) {
            shortSize = height;
            longSize = width;
            mLandscapeRotation = Surface.ROTATION_0;
            mSeascapeRotation = Surface.ROTATION_180;
            if (mContext.getResources().getBoolean(
                    com.android.internal.R.bool.config_reverseDefaultRotation)) {
                mPortraitRotation = Surface.ROTATION_90;
                mUpsideDownRotation = Surface.ROTATION_270;
            } else {
                mPortraitRotation = Surface.ROTATION_270;
                mUpsideDownRotation = Surface.ROTATION_90;
            }
        } else {
            shortSize = width;
            longSize = height;
            mPortraitRotation = Surface.ROTATION_0;
            mUpsideDownRotation = Surface.ROTATION_180;
            if (mContext.getResources().getBoolean(
                    com.android.internal.R.bool.config_reverseDefaultRotation)) {
                mLandscapeRotation = Surface.ROTATION_270;
                mSeascapeRotation = Surface.ROTATION_90;
            } else {
                mLandscapeRotation = Surface.ROTATION_90;
                mSeascapeRotation = Surface.ROTATION_270;
            }
        }
        mStatusBarHeight = mContext.getResources().getDimensionPixelSize(
                com.android.internal.R.dimen.status_bar_height);
        // Height of the navigation bar when presented horizontally at bottom
        mNavigationBarHeightForRotation[mPortraitRotation] =
        mNavigationBarHeightForRotation[mUpsideDownRotation] =
                mContext.getResources().getDimensionPixelSize(
                        com.android.internal.R.dimen.navigation_bar_height);
        mNavigationBarHeightForRotation[mLandscapeRotation] =
        mNavigationBarHeightForRotation[mSeascapeRotation] =
                mContext.getResources().getDimensionPixelSize(
                        com.android.internal.R.dimen.navigation_bar_height_landscape);
        // Width of the navigation bar when presented vertically along one side
        mNavigationBarWidthForRotation[mPortraitRotation] =
        mNavigationBarWidthForRotation[mUpsideDownRotation] =
        mNavigationBarWidthForRotation[mLandscapeRotation] =
        mNavigationBarWidthForRotation[mSeascapeRotation] =
                mContext.getResources().getDimensionPixelSize(
                        com.android.internal.R.dimen.navigation_bar_width);
        // SystemUI (status bar) layout policy
        int shortSizeDp = shortSize * DisplayMetrics.DENSITY_DEFAULT / density;
        if (shortSizeDp < 600) {
            // 0-599dp: "phone" UI with a separate status & navigation bar
            mHasSystemNavBar = false;
            mNavigationBarCanMove = false;//原来的值为true
        } else if (shortSizeDp < 720) {
            // 600+dp: "phone" UI with modifications for larger screens
            mHasSystemNavBar = false;
            mNavigationBarCanMove = false;
        }