Android(安卓)UI开发第三十二篇——Creating a Navigation Drawer

Navigation Drawer是从屏幕的左侧滑出，显示应用导航的视图。官方是这样定义的：

The navigation drawer is a panel that displays the app’s main     navigation options on the left edge of the screen. It is hidden     most of the time, but is revealed when the user swipes a finger     from the left edge of the screen or, while at the top level of the     app, the user touches the app icon in the action bar.

如下图指示：

Navigation Drawer不同于SlidingDrawer，它不存在可以拖动的handle；它也不同于SlidingMenu，Navigation Drawer滑出时主屏幕视图不一定。Navigation Drawer是覆盖在主视图上的。

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 Drawerdesign guide。

Create a Drawer Layout

创建Navigation Drawer需要用DrawerLayout作为界面根控件。在DrawerLayout里面第一个View为当前界面主内容；第二个和第三个View为Navigation Drawer内容。如果当前界面只需要一个Navigation Drawer，则第三个View可以省略。

下面的例子中DrawerLayout里面包含两个View，第一个FrameLayout中是当前界面主要内容显示区域；第二个ListView为Navigation Drawer内容。

<android.support.v4.widget.DrawerLayout    xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/drawer_layout"    android:layout_width="match_parent"    android:layout_height="match_parent">    <!-- The main content view -->    <FrameLayout        android:id="@+id/content_frame"        android:layout_width="match_parent"        android:layout_height="match_parent" />    <!-- The navigation drawer -->    <ListView android:id="@+id/left_drawer"        android:layout_width="240dp"        android:layout_height="match_parent"        android:layout_gravity="start"        android:choiceMode="singleChoice"        android:divider="@android:color/transparent"        android:dividerHeight="0dp"        android:background="#111"/></android.support.v4.widget.DrawerLayout>

上面的代码中有如下几点需要注意：

1、显示界面主要内容的View (上面的FrameLayout)必须为DrawerLayout的第一个子View，原因在于 XML 布局文件中的View顺序为Android系统中的 z-ordering顺序，而Navigation Drawer必须出现在内容之上。
2、显示界面内容的View宽度和高度设置为和父View一样，原因在于当Navigation Drawer不可见的时候，界面内容代表整个界面UI。
3、Navigation Drawer (上面的ListView)必须使用android:layout_gravity属性设置水平的 gravity值.如果要支持 right-to-left (RTL，从右向左阅读)语言用"start"代替"left"(当在 RTL语言运行时候，菜单出现在右侧)。
4、抽屉菜单的宽度为dp单位而高度和父View一样。抽屉菜单的宽度应该不超过320dp，这样用户可以在菜单打开的时候看到部分内容界面。

Initialize the Drawer List

在您的Activity中需要先初始化Navigation Drawer内容，根据您的应用需要Navigation Drawer的内容可能不是ListView，可以使用其他View。

在上面的示例中，我们需要给Navigation Drawer的ListView设置一个Adapter来提供数据。如下所示：

public class MainActivity extends Activity {    private String[] mPlanetTitles;    private DrawerLayout mDrawerLayout;    private ListView mDrawerList;    ...    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mPlanetTitles = getResources().getStringArray(R.array.planets_array);        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);        mDrawerList = (ListView) findViewById(R.id.left_drawer);        // Set the adapter for the list view        mDrawerList.setAdapter(new ArrayAdapter<String>(this,                R.layout.drawer_list_item, mPlanetTitles));        // Set the list's click listener        mDrawerList.setOnItemClickListener(new DrawerItemClickListener());        ...    }}

上面的代码调用了setOnItemClickListener()函数来接受Navigation Drawer点击事件。下面会介绍如何通过点击Navigation Drawer显示主界面内容。

Handle Navigation Click Events

当用户选择Navigation DrawerList中的条目时，系统会调用 OnItemClickListener的, android.view.View, int, long)" target="_blank">onItemClick()函数。

根据您的应用需要，onItemClick函数的实现方式可能不同。下面的示例中，选择Navigation Drawer条目会在程序主界面中插入不同的Fragment。

private class DrawerItemClickListener implements ListView.OnItemClickListener {    @Override    public void onItemClick(AdapterView parent, View view, int position, long id) {        selectItem(position);    }}/** Swaps fragments in the main content view */private void selectItem(int position) {    // Create a new fragment and specify the planet to show based on position    Fragment fragment = new PlanetFragment();    Bundle args = new Bundle();    args.putInt(PlanetFragment.ARG_PLANET_NUMBER, position);    fragment.setArguments(args);    // Insert the fragment by replacing any existing fragment    FragmentManager fragmentManager = getFragmentManager();    fragmentManager.beginTransaction()                   .replace(R.id.content_frame, fragment)                   .commit();    // Highlight the selected item, update the title, and close the drawer    mDrawerList.setItemChecked(position, true);    setTitle(mPlanetTitles[position]);    mDrawerLayout.closeDrawer(mDrawerList);}@Overridepublic void setTitle(CharSequence title) {    mTitle = title;    getActionBar().setTitle(mTitle);}

Listen for Open and Close Events

如果需要监听菜单打开关闭事件，则需要调用DrawerLayout类的setDrawerListener()函数，参数为DrawerLayout.DrawerListener接口的实现。该接口提供了菜单打开关闭等事件的回调函数，例如onDrawerOpened()和onDrawerClosed().

如果您的Activity使用了action bar，则您可以使用Support库提供的ActionBarDrawerToggle类，该类实现了DrawerLayout.DrawerListener接口，并且您还可以根据需要重写相关的函数。该类实现了菜单和Action bar相关的操作。

根据在Navigation Drawer设计指南中的介绍，当菜单显示的时候您应该根据情况隐藏ActionBar上的功能菜单并且修改ActionBar的标题。下面的代码演示了如何重写ActionBarDrawerToggle类的相关函数来实现该功能。

public class MainActivity extends Activity {    private DrawerLayout mDrawerLayout;    private ActionBarDrawerToggle mDrawerToggle;    private CharSequence mDrawerTitle;    private CharSequence mTitle;    ...    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        ...        mTitle = mDrawerTitle = getTitle();        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);        mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,                R.drawable.ic_drawer, R.string.drawer_open, R.string.drawer_close) {            /** Called when a drawer has settled in a completely closed state. */            public void onDrawerClosed(View view) {                getActionBar().setTitle(mTitle);                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()            }            /** Called when a drawer has settled in a completely open state. */            public void onDrawerOpened(View drawerView) {                getActionBar().setTitle(mDrawerTitle);                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()            }        };        // Set the drawer toggle as the DrawerListener        mDrawerLayout.setDrawerListener(mDrawerToggle);    }    /* Called whenever we call invalidateOptionsMenu() */    @Override    public boolean onPrepareOptionsMenu(Menu menu) {        // If the nav drawer is open, hide action items related to the content view        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);        menu.findItem(R.id.action_websearch).setVisible(!drawerOpen);        return super.onPrepareOptionsMenu(menu);    }}

Open and Close with the App Icon

用户可以从屏幕边缘滑动来打开Navigation Drawer，如果您使用了action bar，应该让用户通过点击应用图标也可以打开抽屉菜单。并且应用图标也应该使用一个特殊的图标来指示抽屉菜单。您可以使用ActionBarDrawerToggle类来实现这些功能。

使用ActionBarDrawerToggle，先通过其构造函数来创建该对象，构造函数需要如下参数：

1）显示Navigation Drawer的Activity对象
2）DrawerLayout对象
3）一个用来指示Navigation Drawer的 drawable资源
4）一个用来描述打开Navigation Drawer的文本 (用于支持可访问性)。
5）一个用来描述关闭Navigation Drawer的文本(用于支持可访问性).

无论你是否继承ActionBarDrawerToggle来实现Navigation Drawer监听器，您都需要在Activity的生命周期函数中调用ActionBarDrawerToggle的一些函数。

如下所示：

public class MainActivity extends Activity {    private DrawerLayout mDrawerLayout;    private ActionBarDrawerToggle mDrawerToggle;    ...    public void onCreate(Bundle savedInstanceState) {        ...        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);        mDrawerToggle = new ActionBarDrawerToggle(                this,                  /* host Activity */                mDrawerLayout,         /* DrawerLayout object */                R.drawable.ic_drawer,  /* nav drawer icon to replace 'Up' caret */                R.string.drawer_open,  /* "open drawer" description */                R.string.drawer_close  /* "close drawer" description */                ) {            /** Called when a drawer has settled in a completely closed state. */            public void onDrawerClosed(View view) {                getActionBar().setTitle(mTitle);            }            /** Called when a drawer has settled in a completely open state. */            public void onDrawerOpened(View drawerView) {                getActionBar().setTitle(mDrawerTitle);            }        };        // Set the drawer toggle as the DrawerListener        mDrawerLayout.setDrawerListener(mDrawerToggle);        getActionBar().setDisplayHomeAsUpEnabled(true);        getActionBar().setHomeButtonEnabled(true);    }    @Override    protected void onPostCreate(Bundle savedInstanceState) {        super.onPostCreate(savedInstanceState);        // Sync the toggle state after onRestoreInstanceState has occurred.        mDrawerToggle.syncState();    }    @Override    public void onConfigurationChanged(Configuration newConfig) {        super.onConfigurationChanged(newConfig);        mDrawerToggle.onConfigurationChanged(newConfig);    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        // Pass the event to ActionBarDrawerToggle, if it returns        // true, then it has handled the app icon touch event        if (mDrawerToggle.onOptionsItemSelected(item)) {          return true;        }        // Handle your other action bar items...        return super.onOptionsItemSelected(item);    }    ...}

/** * @author 张兴业 * http://blog.csdn.net/xyz_lmn * iOS入门群：83702688
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代码下载：demo

参考：

https://developer.android.com/reference/android/support/v4/widget/DrawerLayout.html

http://developer.android.com/training/implementing-navigation/nav-drawer.html

http://developer.android.com/design/patterns/navigation-drawer.html

Create a Drawer Layout

Initialize the Drawer List

Handle Navigation Click Events

Listen for Open and Close Events

Open and Close with the App Icon

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