Android--NavigationView基本使用及源码分析

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="Hello World!" />

    <android.support.design.widget.NavigationView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:headerLayout="@layout/layout_header"
        app:menu="@menu/menu"></android.support.design.widget.NavigationView>

</android.support.v4.widget.DrawerLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical">

    <ImageView
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:src="@drawable/ic_account_circle_black_24dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="登录" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:icon="@drawable/ic_account_circle_black_24dp"
        android:title="我的" />
    <item
        android:icon="@drawable/ic_account_circle_black_24dp"
        android:title="安全" />
    <item
        android:icon="@drawable/ic_account_circle_black_24dp"
        android:title="收藏" />
    <item
        android:icon="@drawable/ic_account_circle_black_24dp"
        android:title="设置" />
</menu>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:icon="@drawable/ic_account_circle_black_24dp"
        android:title="我的" />
    <item
        android:icon="@drawable/ic_account_circle_black_24dp"
        android:title="安全" />

    <group android:id="@+id/gp">
        <item
            android:icon="@drawable/ic_account_circle_black_24dp"
            android:title="收藏" />
        <item
            android:icon="@drawable/ic_account_circle_black_24dp"
            android:title="设置" />
    </group>
</menu>

nv_slide.setItemIconTintList(null);

    private final NavigationMenu mMenu;
    private final NavigationMenuPresenter mPresenter = new NavigationMenuPresenter();

    public NavigationView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        ThemeUtils.checkAppCompatTheme(context);

        // Create the menu
        mMenu = new NavigationMenu(context);

        // Custom attributes
        TintTypedArray a = TintTypedArray.obtainStyledAttributes(context, attrs,
                R.styleable.NavigationView, defStyleAttr,
                R.style.Widget_Design_NavigationView);

        ViewCompat.setBackground(
                this, a.getDrawable(R.styleable.NavigationView_android_background));
        if (a.hasValue(R.styleable.NavigationView_elevation)) {
            ViewCompat.setElevation(this, a.getDimensionPixelSize(
                    R.styleable.NavigationView_elevation, 0));
        }
        ViewCompat.setFitsSystemWindows(this,
                a.getBoolean(R.styleable.NavigationView_android_fitsSystemWindows, false));

        mMaxWidth = a.getDimensionPixelSize(R.styleable.NavigationView_android_maxWidth, 0);

        final ColorStateList itemIconTint;
        if (a.hasValue(R.styleable.NavigationView_itemIconTint)) {
            itemIconTint = a.getColorStateList(R.styleable.NavigationView_itemIconTint);
        } else {
            itemIconTint = createDefaultColorStateList(android.R.attr.textColorSecondary);
        }

        boolean textAppearanceSet = false;
        int textAppearance = 0;
        if (a.hasValue(R.styleable.NavigationView_itemTextAppearance)) {
            textAppearance = a.getResourceId(R.styleable.NavigationView_itemTextAppearance, 0);
            textAppearanceSet = true;
        }

        ColorStateList itemTextColor = null;
        if (a.hasValue(R.styleable.NavigationView_itemTextColor)) {
            itemTextColor = a.getColorStateList(R.styleable.NavigationView_itemTextColor);
        }

        if (!textAppearanceSet && itemTextColor == null) {
            // If there isn't a text appearance set, we'll use a default text color
            itemTextColor = createDefaultColorStateList(android.R.attr.textColorPrimary);
        }

        final Drawable itemBackground = a.getDrawable(R.styleable.NavigationView_itemBackground);

        mMenu.setCallback(new MenuBuilder.Callback() {
            @Override
            public boolean onMenuItemSelected(MenuBuilder menu, MenuItem item) {
                return mListener != null && mListener.onNavigationItemSelected(item);
            }

            @Override
            public void onMenuModeChange(MenuBuilder menu) {}
        });
        mPresenter.setId(PRESENTER_NAVIGATION_VIEW_ID);
        mPresenter.initForMenu(context, mMenu);
        mPresenter.setItemIconTintList(itemIconTint);
        if (textAppearanceSet) {
            mPresenter.setItemTextAppearance(textAppearance);
        }
        mPresenter.setItemTextColor(itemTextColor);
        mPresenter.setItemBackground(itemBackground);
        mMenu.addMenuPresenter(mPresenter);
        addView((View) mPresenter.getMenuView(this));

        if (a.hasValue(R.styleable.NavigationView_menu)) {
            inflateMenu(a.getResourceId(R.styleable.NavigationView_menu, 0));
        }

        if (a.hasValue(R.styleable.NavigationView_headerLayout)) {
            inflateHeaderView(a.getResourceId(R.styleable.NavigationView_headerLayout, 0));
        }

        a.recycle();
    }

    @Override
    public void initForMenu(Context context, MenuBuilder menu) {
        mLayoutInflater = LayoutInflater.from(context);
        mMenu = menu;
        Resources res = context.getResources();
        mPaddingSeparator = res.getDimensionPixelOffset(
                R.dimen.design_navigation_separator_vertical_padding);
    }

    @Override
    public MenuView getMenuView(ViewGroup root) {
        if (mMenuView == null) {
            mMenuView = (NavigationMenuView) mLayoutInflater.inflate(
                    R.layout.design_navigation_menu, root, false);
            if (mAdapter == null) {
                mAdapter = new NavigationMenuAdapter();
            }
            mHeaderLayout = (LinearLayout) mLayoutInflater
                    .inflate(R.layout.design_navigation_item_header,
                            mMenuView, false);
            mMenuView.setAdapter(mAdapter);
        }
        return mMenuView;
    }

public class NavigationMenuView extends RecyclerView implements MenuView {

    public NavigationMenuView(Context context) {
        this(context, null);
    }

    public NavigationMenuView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public NavigationMenuView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setLayoutManager(new LinearLayoutManager(context, LinearLayoutManager.VERTICAL, false));
    }

    @Override
    public void initialize(MenuBuilder menu) {

    }

    @Override
    public int getWindowAnimations() {
        return 0;
    }

}

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2015 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
-->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:id="@+id/navigation_header_container"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical"
      android:paddingBottom="@dimen/design_navigation_separator_vertical_padding" />

    public NavigationView(Context context, AttributeSet attrs, int defStyleAttr) {
        ...

        if (a.hasValue(R.styleable.NavigationView_menu)) {
            inflateMenu(a.getResourceId(R.styleable.NavigationView_menu, 0));
        }

        if (a.hasValue(R.styleable.NavigationView_headerLayout)) {
            inflateHeaderView(a.getResourceId(R.styleable.NavigationView_headerLayout, 0));
        }

        a.recycle();
    }

    /**
     * Inflate a menu resource into this navigation view.
     *
     * <p>Existing items in the menu will not be modified or removed.</p>
     *
     * @param resId ID of a menu resource to inflate
     */
    public void inflateMenu(int resId) {
        mPresenter.setUpdateSuspended(true);
        getMenuInflater().inflate(resId, mMenu);
        mPresenter.setUpdateSuspended(false);
        mPresenter.updateMenuView(false);
    }

    /**
     * Inflate a menu hierarchy from the specified XML resource. Throws
     * {@link InflateException} if there is an error.
     *
     * @param menuRes Resource ID for an XML layout resource to load (e.g.,
     *            <code>R.menu.main_activity</code>)
     * @param menu The Menu to inflate into. The items and submenus will be
     *            added to this Menu.
     */
    public void inflate(@MenuRes int menuRes, Menu menu) {
        XmlResourceParser parser = null;
        try {
            parser = mContext.getResources().getLayout(menuRes);
            AttributeSet attrs = Xml.asAttributeSet(parser);

            parseMenu(parser, attrs, menu);
        } catch (XmlPullParserException e) {
            throw new InflateException("Error inflating menu XML", e);
        } catch (IOException e) {
            throw new InflateException("Error inflating menu XML", e);
        } finally {
            if (parser != null) parser.close();
        }
    }

    /**
     * Called internally to fill the given menu. If a sub menu is seen, it will
     * call this recursively.
     */
    private void parseMenu(XmlPullParser parser, AttributeSet attrs, Menu menu)
            throws XmlPullParserException, IOException {
        MenuState menuState = new MenuState(menu);

        int eventType = parser.getEventType();
        String tagName;
        boolean lookingForEndOfUnknownTag = false;
        String unknownTagName = null;

        // This loop will skip to the menu start tag
        do {
            if (eventType == XmlPullParser.START_TAG) {
                tagName = parser.getName();
                if (tagName.equals(XML_MENU)) {
                    // Go to next tag
                    eventType = parser.next();
                    break;
                }

                throw new RuntimeException("Expecting menu, got " + tagName);
            }
            eventType = parser.next();
        } while (eventType != XmlPullParser.END_DOCUMENT);

        boolean reachedEndOfMenu = false;
        while (!reachedEndOfMenu) {
            switch (eventType) {
                case XmlPullParser.START_TAG:
                    if (lookingForEndOfUnknownTag) {
                        break;
                    }

                    tagName = parser.getName();
                    if (tagName.equals(XML_GROUP)) {
                        menuState.readGroup(attrs);
                    } else if (tagName.equals(XML_ITEM)) {
                        menuState.readItem(attrs);
                    } else if (tagName.equals(XML_MENU)) {
                        // A menu start tag denotes a submenu for an item
                        SubMenu subMenu = menuState.addSubMenuItem();
                        registerMenu(subMenu, attrs);

                        // Parse the submenu into returned SubMenu
                        parseMenu(parser, attrs, subMenu);
                    } else {
                        lookingForEndOfUnknownTag = true;
                        unknownTagName = tagName;
                    }
                    break;

                case XmlPullParser.END_TAG:
                    tagName = parser.getName();
                    if (lookingForEndOfUnknownTag && tagName.equals(unknownTagName)) {
                        lookingForEndOfUnknownTag = false;
                        unknownTagName = null;
                    } else if (tagName.equals(XML_GROUP)) {
                        menuState.resetGroup();
                    } else if (tagName.equals(XML_ITEM)) {
                        // Add the item if it hasn't been added (if the item was
                        // a submenu, it would have been added already)
                        if (!menuState.hasAddedItem()) {
                            if (menuState.itemActionProvider != null &&
                                    menuState.itemActionProvider.hasSubMenu()) {
                                registerMenu(menuState.addSubMenuItem(), attrs);
                            } else {
                                registerMenu(menuState.addItem(), attrs);
                            }
                        }
                    } else if (tagName.equals(XML_MENU)) {
                        reachedEndOfMenu = true;
                    }
                    break;

                case XmlPullParser.END_DOCUMENT:
                    throw new RuntimeException("Unexpected end of document");
            }

            eventType = parser.next();
        }
    }

    @Override
    public void updateMenuView(boolean cleared) {
        if (mAdapter != null) {
            mAdapter.update();
        }
    }

    public NavigationView(Context context, AttributeSet attrs, int defStyleAttr) {
       ...

        if (a.hasValue(R.styleable.NavigationView_headerLayout)) {
            inflateHeaderView(a.getResourceId(R.styleable.NavigationView_headerLayout, 0));
        }

        a.recycle();
    }

    /**
     * Inflates a View and add it as a header of the navigation menu.
     *
     * @param res The layout resource ID.
     * @return a newly inflated View.
     */
    public View inflateHeaderView(@LayoutRes int res) {
        return mPresenter.inflateHeaderView(res);
    }

    public View inflateHeaderView(@LayoutRes int res) {
        View view = mLayoutInflater.inflate(res, mHeaderLayout, false);
        addHeaderView(view);
        return view;
    }

    public void addHeaderView(@NonNull View view) {
        mHeaderLayout.addView(view);
        // The padding on top should be cleared.
        mMenuView.setPadding(0, 0, 0, mMenuView.getPaddingBottom());
    }

    private class NavigationMenuAdapter extends RecyclerView.Adapter<ViewHolder> {

        private static final String STATE_CHECKED_ITEM = "android:menu:checked";

        private static final String STATE_ACTION_VIEWS = "android:menu:action_views";
        private static final int VIEW_TYPE_NORMAL = 0;
        private static final int VIEW_TYPE_SUBHEADER = 1;
        private static final int VIEW_TYPE_SEPARATOR = 2;
        private static final int VIEW_TYPE_HEADER = 3;

        private final ArrayList<NavigationMenuItem> mItems = new ArrayList<>();
        private MenuItemImpl mCheckedItem;
        private boolean mUpdateSuspended;

        NavigationMenuAdapter() {
            prepareMenuItems();
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public int getItemCount() {
            return mItems.size();
        }

        @Override
        public int getItemViewType(int position) {
            NavigationMenuItem item = mItems.get(position);
            if (item instanceof NavigationMenuSeparatorItem) {
                return VIEW_TYPE_SEPARATOR;
            } else if (item instanceof NavigationMenuHeaderItem) {
                return VIEW_TYPE_HEADER;
            } else if (item instanceof NavigationMenuTextItem) {
                NavigationMenuTextItem textItem = (NavigationMenuTextItem) item;
                if (textItem.getMenuItem().hasSubMenu()) {
                    return VIEW_TYPE_SUBHEADER;
                } else {
                    return VIEW_TYPE_NORMAL;
                }
            }
            throw new RuntimeException("Unknown item type.");
        }

        @Override
        public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            switch (viewType) {
                case VIEW_TYPE_NORMAL:
                    return new NormalViewHolder(mLayoutInflater, parent, mOnClickListener);
                case VIEW_TYPE_SUBHEADER:
                    return new SubheaderViewHolder(mLayoutInflater, parent);
                case VIEW_TYPE_SEPARATOR:
                    return new SeparatorViewHolder(mLayoutInflater, parent);
                case VIEW_TYPE_HEADER:
                    return new HeaderViewHolder(mHeaderLayout);
            }
            return null;
        }

        @Override
        public void onBindViewHolder(ViewHolder holder, int position) {
            switch (getItemViewType(position)) {
                case VIEW_TYPE_NORMAL: {
                    NavigationMenuItemView itemView = (NavigationMenuItemView) holder.itemView;
                    itemView.setIconTintList(mIconTintList);
                    if (mTextAppearanceSet) {
                        itemView.setTextAppearance(mTextAppearance);
                    }
                    if (mTextColor != null) {
                        itemView.setTextColor(mTextColor);
                    }
                    ViewCompat.setBackground(itemView, mItemBackground != null ?
                            mItemBackground.getConstantState().newDrawable() : null);
                    NavigationMenuTextItem item = (NavigationMenuTextItem) mItems.get(position);
                    itemView.setNeedsEmptyIcon(item.needsEmptyIcon);
                    itemView.initialize(item.getMenuItem(), 0);
                    break;
                }
                case VIEW_TYPE_SUBHEADER: {
                    TextView subHeader = (TextView) holder.itemView;
                    NavigationMenuTextItem item = (NavigationMenuTextItem) mItems.get(position);
                    subHeader.setText(item.getMenuItem().getTitle());
                    break;
                }
                case VIEW_TYPE_SEPARATOR: {
                    NavigationMenuSeparatorItem item =
                            (NavigationMenuSeparatorItem) mItems.get(position);
                    holder.itemView.setPadding(0, item.getPaddingTop(), 0,
                            item.getPaddingBottom());
                    break;
                }
                case VIEW_TYPE_HEADER: {
                    break;
                }
            }

        }

        @Override
        public void onViewRecycled(ViewHolder holder) {
            if (holder instanceof NormalViewHolder) {
                ((NavigationMenuItemView) holder.itemView).recycle();
            }
        }

        public void update() {
            prepareMenuItems();
            notifyDataSetChanged();
        }

        /**
         * Flattens the visible menu items of {@link #mMenu} into {@link #mItems},
         * while inserting separators between items when necessary.
         */
        private void prepareMenuItems() {
            if (mUpdateSuspended) {
                return;
            }
            mUpdateSuspended = true;
            mItems.clear();
            mItems.add(new NavigationMenuHeaderItem());

            int currentGroupId = -1;
            int currentGroupStart = 0;
            boolean currentGroupHasIcon = false;
            for (int i = 0, totalSize = mMenu.getVisibleItems().size(); i < totalSize; i++) {
                MenuItemImpl item = mMenu.getVisibleItems().get(i);
                if (item.isChecked()) {
                    setCheckedItem(item);
                }
                if (item.isCheckable()) {
                    item.setExclusiveCheckable(false);
                }
                if (item.hasSubMenu()) {
                    SubMenu subMenu = item.getSubMenu();
                    if (subMenu.hasVisibleItems()) {
                        if (i != 0) {
                            mItems.add(new NavigationMenuSeparatorItem(mPaddingSeparator, 0));
                        }
                        mItems.add(new NavigationMenuTextItem(item));
                        boolean subMenuHasIcon = false;
                        int subMenuStart = mItems.size();
                        for (int j = 0, size = subMenu.size(); j < size; j++) {
                            MenuItemImpl subMenuItem = (MenuItemImpl) subMenu.getItem(j);
                            if (subMenuItem.isVisible()) {
                                if (!subMenuHasIcon && subMenuItem.getIcon() != null) {
                                    subMenuHasIcon = true;
                                }
                                if (subMenuItem.isCheckable()) {
                                    subMenuItem.setExclusiveCheckable(false);
                                }
                                if (item.isChecked()) {
                                    setCheckedItem(item);
                                }
                                mItems.add(new NavigationMenuTextItem(subMenuItem));
                            }
                        }
                        if (subMenuHasIcon) {
                            appendTransparentIconIfMissing(subMenuStart, mItems.size());
                        }
                    }
                } else {
                    int groupId = item.getGroupId();
                    if (groupId != currentGroupId) { // first item in group
                        currentGroupStart = mItems.size();
                        currentGroupHasIcon = item.getIcon() != null;
                        if (i != 0) {
                            currentGroupStart++;
                            mItems.add(new NavigationMenuSeparatorItem(
                                    mPaddingSeparator, mPaddingSeparator));
                        }
                    } else if (!currentGroupHasIcon && item.getIcon() != null) {
                        currentGroupHasIcon = true;
                        appendTransparentIconIfMissing(currentGroupStart, mItems.size());
                    }
                    NavigationMenuTextItem textItem = new NavigationMenuTextItem(item);
                    textItem.needsEmptyIcon = currentGroupHasIcon;
                    mItems.add(textItem);
                    currentGroupId = groupId;
                }
            }
            mUpdateSuspended = false;
        }

        private void appendTransparentIconIfMissing(int startIndex, int endIndex) {
            for (int i = startIndex; i < endIndex; i++) {
                NavigationMenuTextItem textItem = (NavigationMenuTextItem) mItems.get(i);
                textItem.needsEmptyIcon = true;
            }
        }

        public void setCheckedItem(MenuItemImpl checkedItem) {
            if (mCheckedItem == checkedItem || !checkedItem.isCheckable()) {
                return;
            }
            if (mCheckedItem != null) {
                mCheckedItem.setChecked(false);
            }
            mCheckedItem = checkedItem;
            checkedItem.setChecked(true);
        }

        public Bundle createInstanceState() {
            Bundle state = new Bundle();
            if (mCheckedItem != null) {
                state.putInt(STATE_CHECKED_ITEM, mCheckedItem.getItemId());
            }
            // Store the states of the action views.
            SparseArray<ParcelableSparseArray> actionViewStates = new SparseArray<>();
            for (int i = 0, size = mItems.size(); i < size; i++) {
                NavigationMenuItem navigationMenuItem = mItems.get(i);
                if (navigationMenuItem instanceof NavigationMenuTextItem) {
                    MenuItemImpl item = ((NavigationMenuTextItem) navigationMenuItem).getMenuItem();
                    View actionView = item != null ? item.getActionView() : null;
                    if (actionView != null) {
                        ParcelableSparseArray container = new ParcelableSparseArray();
                        actionView.saveHierarchyState(container);
                        actionViewStates.put(item.getItemId(), container);
                    }
                }
            }
            state.putSparseParcelableArray(STATE_ACTION_VIEWS, actionViewStates);
            return state;
        }

        public void restoreInstanceState(Bundle state) {
            int checkedItem = state.getInt(STATE_CHECKED_ITEM, 0);
            if (checkedItem != 0) {
                mUpdateSuspended = true;
                for (int i = 0, size = mItems.size(); i < size; i++) {
                    NavigationMenuItem item = mItems.get(i);
                    if (item instanceof NavigationMenuTextItem) {
                        MenuItemImpl menuItem = ((NavigationMenuTextItem) item).getMenuItem();
                        if (menuItem != null && menuItem.getItemId() == checkedItem) {
                            setCheckedItem(menuItem);
                            break;
                        }
                    }
                }
                mUpdateSuspended = false;
                prepareMenuItems();
            }
            // Restore the states of the action views.
            SparseArray<ParcelableSparseArray> actionViewStates = state
                    .getSparseParcelableArray(STATE_ACTION_VIEWS);
            if (actionViewStates != null) {
                for (int i = 0, size = mItems.size(); i < size; i++) {
                    NavigationMenuItem navigationMenuItem = mItems.get(i);
                    if (!(navigationMenuItem instanceof NavigationMenuTextItem)) {
                        continue;
                    }
                    MenuItemImpl item = ((NavigationMenuTextItem) navigationMenuItem).getMenuItem();
                    if (item == null) {
                        continue;
                    }
                    View actionView = item.getActionView();
                    if (actionView == null) {
                        continue;
                    }
                    ParcelableSparseArray container = actionViewStates.get(item.getItemId());
                    if (container == null) {
                        continue;
                    }
                    actionView.restoreHierarchyState(container);
                }
            }
        }

        public void setUpdateSuspended(boolean updateSuspended) {
            mUpdateSuspended = updateSuspended;
        }

    }

        @Override
        public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            switch (viewType) {
                case VIEW_TYPE_NORMAL:
                    return new NormalViewHolder(mLayoutInflater, parent, mOnClickListener);
                case VIEW_TYPE_SUBHEADER:
                    return new SubheaderViewHolder(mLayoutInflater, parent);
                case VIEW_TYPE_SEPARATOR:
                    return new SeparatorViewHolder(mLayoutInflater, parent);
                case VIEW_TYPE_HEADER:
                    return new HeaderViewHolder(mHeaderLayout);
            }
            return null;
        }

        public void update() {
            prepareMenuItems();
            notifyDataSetChanged();
        }

        /**
         * Flattens the visible menu items of {@link #mMenu} into {@link #mItems},
         * while inserting separators between items when necessary.
         */
        private void prepareMenuItems() {
            if (mUpdateSuspended) {
                return;
            }
            mUpdateSuspended = true;
            mItems.clear();
            mItems.add(new NavigationMenuHeaderItem());

            int currentGroupId = -1;
            int currentGroupStart = 0;
            boolean currentGroupHasIcon = false;
            for (int i = 0, totalSize = mMenu.getVisibleItems().size(); i < totalSize; i++) {
                MenuItemImpl item = mMenu.getVisibleItems().get(i);
                if (item.isChecked()) {
                    setCheckedItem(item);
                }
                if (item.isCheckable()) {
                    item.setExclusiveCheckable(false);
                }
                if (item.hasSubMenu()) {
                    SubMenu subMenu = item.getSubMenu();
                    if (subMenu.hasVisibleItems()) {
                        if (i != 0) {
                            mItems.add(new NavigationMenuSeparatorItem(mPaddingSeparator, 0));
                        }
                        mItems.add(new NavigationMenuTextItem(item));
                        boolean subMenuHasIcon = false;
                        int subMenuStart = mItems.size();
                        for (int j = 0, size = subMenu.size(); j < size; j++) {
                            MenuItemImpl subMenuItem = (MenuItemImpl) subMenu.getItem(j);
                            if (subMenuItem.isVisible()) {
                                if (!subMenuHasIcon && subMenuItem.getIcon() != null) {
                                    subMenuHasIcon = true;
                                }
                                if (subMenuItem.isCheckable()) {
                                    subMenuItem.setExclusiveCheckable(false);
                                }
                                if (item.isChecked()) {
                                    setCheckedItem(item);
                                }
                                mItems.add(new NavigationMenuTextItem(subMenuItem));
                            }
                        }
                        if (subMenuHasIcon) {
                            appendTransparentIconIfMissing(subMenuStart, mItems.size());
                        }
                    }
                } else {
                    int groupId = item.getGroupId();
                    if (groupId != currentGroupId) { // first item in group
                        currentGroupStart = mItems.size();
                        currentGroupHasIcon = item.getIcon() != null;
                        if (i != 0) {
                            currentGroupStart++;
                            mItems.add(new NavigationMenuSeparatorItem(
                                    mPaddingSeparator, mPaddingSeparator));
                        }
                    } else if (!currentGroupHasIcon && item.getIcon() != null) {
                        currentGroupHasIcon = true;
                        appendTransparentIconIfMissing(currentGroupStart, mItems.size());
                    }
                    NavigationMenuTextItem textItem = new NavigationMenuTextItem(item);
                    textItem.needsEmptyIcon = currentGroupHasIcon;
                    mItems.add(textItem);
                    currentGroupId = groupId;
                }
            }
            mUpdateSuspended = false;
        }