（4.1.34.1）Navigation Drawer

Navigation Drawer是从屏幕的左侧滑出，显示应用导航的视图，覆盖在主视图上。

Navigation Drawer是Android团对在2013 google IO大会期间更新的Support库（V13）中新加入的重要的功能。

实现现Navigation Drawer需要使用最新支持库（V13）的DrawerLayout。Navigation Drawer的设计指南请参考 

Navigation Drawer design guide，但是当时需要的最低版本14，这就限制了我们的使用，当然可以使用来实现兼容，

这并不是最好的，如今谷歌退出V7来实现兼容低版本，我们不需要额外的其他代码，如果你的sdk更新到22.6.2的话，

在创建一个新的项目的时候，在最后一步创建一个Activity的时候，会让你选择一个主题，其中有一项就是

Navigation Drawer，选中然后创建项目。

我们接下来分析一下，项目内容：

1、布局内容

 <android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:id="@+id/drawer_layout"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context="com.example.androidsampe1.MainActivity" >

     <FrameLayout
         android:id="@+id/container"
         android:layout_width="match_parent"
         android:layout_height="match_parent" />


     <fragment
         android:id="@+id/navigation_drawer"
         android:name="com.example.androidsampe1.NavigationDrawerFragment"
         android:layout_width="@dimen/navigation_drawer_width"
         android:layout_height="match_parent"
         android:layout_gravity="left" />

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

DrawerLayout作为跟布局，要求全屏，有两个子布局，第一个是显示内容，第二个是左边抽屉内容，这里是使用一个

fragment，也可以使用其他的View。

主界面：

MainActivity.java

 package com.example.androidsampe1;

 import android.app.Activity;
 import android.support.v7.app.ActionBarActivity;
 import android.support.v7.app.ActionBar;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentManager;
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
 import android.support.v4.widget.DrawerLayout;
 import android.widget.TextView;

 public class MainActivity extends ActionBarActivity
         implements NavigationDrawerFragment.NavigationDrawerCallbacks {

     /**
      * 这个Fragment管理行为、交互和演示导航的抽屉
      * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
      */
     private NavigationDrawerFragment mNavigationDrawerFragment;

     /**
      * 用来存储上一个屏幕的标题
      * Used to store the last screen title. For use in {@link #restoreActionBar()}.
      */
     private CharSequence mTitle;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);

         mNavigationDrawerFragment = (NavigationDrawerFragment)
                 getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
         mTitle = getTitle();

         // Set up the drawer. 建立抽屉
         mNavigationDrawerFragment.setUp(
                 R.id.navigation_drawer,
                 (DrawerLayout) findViewById(R.id.drawer_layout));
     }
     //这里切换布局的地方，根据position，我们可以选择要替换的fragment
     @Override
     public void onNavigationDrawerItemSelected(int position) {
         // update the main content by replacing fragments
         FragmentManager fragmentManager = getSupportFragmentManager();
         fragmentManager.beginTransaction()
                 .replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
                 .commit();
     }

     public void onSectionAttached(int number) {
         switch (number) {
             case 1:
                 mTitle = getString(R.string.title_section1);
                 break;
             case 2:
                 mTitle = getString(R.string.title_section2);
                 break;
             case 3:
                 mTitle = getString(R.string.title_section3);
                 break;
         }
     }

     public void restoreActionBar() {
         ActionBar actionBar = getSupportActionBar();
         actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
         actionBar.setDisplayShowTitleEnabled(true);
         actionBar.setTitle(mTitle);
     }


     @Override
     public boolean onCreateOptionsMenu(Menu menu) {
         if (!mNavigationDrawerFragment.isDrawerOpen()) {
             // Only show items in the action bar relevant to this screen
             // if the drawer is not showing. Otherwise, let the drawer
             // decide what to show in the action bar.
             getMenuInflater().inflate(R.menu.main, menu);
             restoreActionBar();
             return true;
         }
         return super.onCreateOptionsMenu(menu);
     }

     @Override
     public boolean onOptionsItemSelected(MenuItem item) {
         // Handle action bar item clicks here. The action bar will
         // automatically handle clicks on the Home/Up button, so long
         // as you specify a parent activity in AndroidManifest.xml.
         int id = item.getItemId();
         if (id == R.id.action_settings) {
             return true;
         }
         return super.onOptionsItemSelected(item);
     }

     /**
      * A placeholder fragment containing a simple view.
      */
     public static class PlaceholderFragment extends Fragment {
         /**
          * The fragment argument representing the section number for this
          * fragment.
          */
         private static final String ARG_SECTION_NUMBER = "section_number";

         /**
          * Returns a new instance of this fragment for the given section
          * number.
          */
         public static PlaceholderFragment newInstance(int sectionNumber) {
             PlaceholderFragment fragment = new PlaceholderFragment();
             Bundle args = new Bundle();
             args.putInt(ARG_SECTION_NUMBER, sectionNumber);
             fragment.setArguments(args);
             return fragment;
         }

         public PlaceholderFragment() {
         }

         @Override
         public View onCreateView(LayoutInflater inflater, ViewGroup container,
                 Bundle savedInstanceState) {
             View rootView = inflater.inflate(R.layout.fragment_main, container, false);
             TextView textView = (TextView) rootView.findViewById(R.id.section_label);
             textView.setText(Integer.toString(getArguments().getInt(ARG_SECTION_NUMBER)));
             return rootView;
         }

         @Override
         public void onAttach(Activity activity) {
             super.onAttach(activity);
             ((MainActivity) activity).onSectionAttached(
                     getArguments().getInt(ARG_SECTION_NUMBER));
         }
     }

 }

NavigationDrawerFragment.java  --左边导航抽屉的布局

 package com.example.androidsampe1;

 import android.support.v7.app.ActionBarActivity;
 import android.app.Activity;
 import android.support.v7.app.ActionBar;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.ActionBarDrawerToggle;
 import android.support.v4.view.GravityCompat;
 import android.support.v4.widget.DrawerLayout;
 import android.content.SharedPreferences;
 import android.content.res.Configuration;
 import android.os.Bundle;
 import android.preference.PreferenceManager;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.AdapterView;
 import android.widget.ArrayAdapter;
 import android.widget.ListView;
 import android.widget.Toast;

 /**
  * Fragment used for managing interactions for and presentation of a navigation drawer.
  * See the <a href="https://developer.android.com/design/patterns/navigation-drawer.html#Interaction">
  * design guidelines</a> for a complete explanation of the behaviors implemented here.
  */
 public class NavigationDrawerFragment extends Fragment {

     /**
      * Remember the position of the selected item.
      */
     private static final String STATE_SELECTED_POSITION = "selected_navigation_drawer_position";

     /**
      * Per the design guidelines, you should show the drawer on launch until the user manually
      * expands it. This shared preference tracks this.
      */
     private static final String PREF_USER_LEARNED_DRAWER = "navigation_drawer_learned";

     /**
      * A pointer to the current callbacks instance (the Activity).
      */
     private NavigationDrawerCallbacks mCallbacks;

     /**
      * Helper component that ties the action bar to the navigation drawer.
      * 这个导航抽屉监听事件的回调接口，监听打开和关闭
      */
     private ActionBarDrawerToggle mDrawerToggle;

     private DrawerLayout mDrawerLayout;
     private ListView mDrawerListView;
     private View mFragmentContainerView;

     private int mCurrentSelectedPosition = 0;
     private boolean mFromSavedInstanceState;
     private boolean mUserLearnedDrawer;

     public NavigationDrawerFragment() {
     }

     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);

         // Read in the flag indicating whether or not the user has demonstrated awareness of the
         // drawer. See PREF_USER_LEARNED_DRAWER for details.
         SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getActivity());
         mUserLearnedDrawer = sp.getBoolean(PREF_USER_LEARNED_DRAWER, false);

         if (savedInstanceState != null) {
             mCurrentSelectedPosition = savedInstanceState.getInt(STATE_SELECTED_POSITION);
             mFromSavedInstanceState = true;
         }

         // Select either the default item (0) or the last selected item.
         selectItem(mCurrentSelectedPosition);
     }

     @Override
     public void onActivityCreated (Bundle savedInstanceState) {
         super.onActivityCreated(savedInstanceState);
         // Indicate that this fragment would like to influence the set of actions in the action bar.
         setHasOptionsMenu(true);
     }

     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
             Bundle savedInstanceState) {
         mDrawerListView = (ListView) inflater.inflate(
                 R.layout.fragment_navigation_drawer, container, false);
         mDrawerListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
             @Override
             public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                 selectItem(position);
             }
         });
         mDrawerListView.setAdapter(new ArrayAdapter<String>(
                 getActionBar().getThemedContext(),
                 android.R.layout.simple_list_item_1,
                 android.R.id.text1,
                 new String[]{
                         getString(R.string.title_section1),
                         getString(R.string.title_section2),
                         getString(R.string.title_section3),
                 }));
         mDrawerListView.setItemChecked(mCurrentSelectedPosition, true);
         return mDrawerListView;
     }

     public boolean isDrawerOpen() {
         return mDrawerLayout != null && mDrawerLayout.isDrawerOpen(mFragmentContainerView);
     }

     /**
      * Users of this fragmentv must call this method to set up the naigation drawer interactions.
      *
      * @param fragmentId   The android:id of this fragment in its activity's layout.
      * @param drawerLayout The DrawerLayout containing this fragment's UI.
      */
     public void setUp(int fragmentId, DrawerLayout drawerLayout) {
         mFragmentContainerView = getActivity().findViewById(fragmentId);
         mDrawerLayout = drawerLayout;

         // set a custom shadow that overlays the main content when the drawer opens
         mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
         // set up the drawer's list view with items and click listener

         ActionBar actionBar = getActionBar();
         actionBar.setDisplayHomeAsUpEnabled(true);
         actionBar.setHomeButtonEnabled(true);

         // ActionBarDrawerToggle ties together the the proper interactions
         // between the navigation drawer and the action bar app icon.
         mDrawerToggle = new ActionBarDrawerToggle(
                 getActivity(),                    /* host Activity */
                 mDrawerLayout,                    /* DrawerLayout object */
                 R.drawable.ic_drawer,             /* nav drawer image to replace 'Up' caret */
                 R.string.navigation_drawer_open,  /* "open drawer" description for accessibility */
                 R.string.navigation_drawer_close  /* "close drawer" description for accessibility */
         ) {
             @Override
             public void onDrawerClosed(View drawerView) {
                 super.onDrawerClosed(drawerView);
                 if (!isAdded()) {
                     return;
                 }

                 getActivity().supportInvalidateOptionsMenu(); // calls onPrepareOptionsMenu()
             }

             @Override
             public void onDrawerOpened(View drawerView) {
                 super.onDrawerOpened(drawerView);
                 if (!isAdded()) {
                     return;
                 }

                 if (!mUserLearnedDrawer) {
                         //存储当前的标志位
                     // The user manually opened the drawer; store this flag to prevent auto-showing
                     // the navigation drawer automatically in the future.
                     mUserLearnedDrawer = true;
                     SharedPreferences sp = PreferenceManager
                             .getDefaultSharedPreferences(getActivity());
                     sp.edit().putBoolean(PREF_USER_LEARNED_DRAWER, true).commit();
                 }

                 getActivity().supportInvalidateOptionsMenu(); // calls onPrepareOptionsMenu()
             }
         };

         // If the user hasn't 'learned' about the drawer, open it to introduce them to the drawer,
         // per the navigation drawer design guidelines.
         if (!mUserLearnedDrawer && !mFromSavedInstanceState) {
             mDrawerLayout.openDrawer(mFragmentContainerView);
         }

         // Defer code dependent on restoration of previous instance state.
         mDrawerLayout.post(new Runnable() {
             @Override
             public void run() {
                 mDrawerToggle.syncState();
             }
         });

         mDrawerLayout.setDrawerListener(mDrawerToggle);
     }

     private void selectItem(int position) {
         mCurrentSelectedPosition = position;
         if (mDrawerListView != null) {
             mDrawerListView.setItemChecked(position, true);
         }
         if (mDrawerLayout != null) {
             mDrawerLayout.closeDrawer(mFragmentContainerView);
         }
         if (mCallbacks != null) {
             mCallbacks.onNavigationDrawerItemSelected(position);
         }
     }

     @Override
     public void onAttach(Activity activity) {
         super.onAttach(activity);
         try {
             mCallbacks = (NavigationDrawerCallbacks) activity;
         } catch (ClassCastException e) {
             throw new ClassCastException("Activity must implement NavigationDrawerCallbacks.");
         }
     }

     @Override
     public void onDetach() {
         super.onDetach();
         mCallbacks = null;
     }

     @Override
     public void onSaveInstanceState(Bundle outState) {
         super.onSaveInstanceState(outState);
         outState.putInt(STATE_SELECTED_POSITION, mCurrentSelectedPosition);
     }

     @Override
     public void onConfigurationChanged(Configuration newConfig) {
         super.onConfigurationChanged(newConfig);
         // Forward the new configuration the drawer toggle component.
         mDrawerToggle.onConfigurationChanged(newConfig);
     }

     @Override
     public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
         // If the drawer is open, show the global app actions in the action bar. See also
         // showGlobalContextActionBar, which controls the top-left area of the action bar.
         if (mDrawerLayout != null && isDrawerOpen()) {
             inflater.inflate(R.menu.global, menu);
             showGlobalContextActionBar();
         }
         super.onCreateOptionsMenu(menu, inflater);
     }

     @Override
     public boolean onOptionsItemSelected(MenuItem item) {
 <span style="white-space:pre">    </span>//监听Home按钮，Home指的是ActionBar左边的按钮
         if (mDrawerToggle.onOptionsItemSelected(item)) {
             return true;
         }

         if (item.getItemId() == R.id.action_example) {
             Toast.makeText(getActivity(), "Example action.", Toast.LENGTH_SHORT).show();
             return true;
         }

         return super.onOptionsItemSelected(item);
     }

     /**
      * Per the navigation drawer design guidelines, updates the action bar to show the global app
      * 'context', rather than just what's in the current screen.
      */
     private void showGlobalContextActionBar() {
         ActionBar actionBar = getActionBar();
         actionBar.setDisplayShowTitleEnabled(true);
         actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
         actionBar.setTitle(R.string.app_name);
     }

     private ActionBar getActionBar() {
         return ((ActionBarActivity) getActivity()).getSupportActionBar();
     }

     /**
      * Callbacks interface that all activities using this fragment must implement.
      */
     public static interface NavigationDrawerCallbacks {
         /**
          * Called when an item in the navigation drawer is selected.
          */
         void onNavigationDrawerItemSelected(int position);
     }
 }

总的来说，框架在V7中已经给出了，我们只需要修改左边导航抽屉的显示内容，已经主界面切换的Fragment就可以了，

这样减少了开发的难度，提高开发效率。