Android DrawerLayout implements drawer effect example code

<?xml version="1.0" encoding="utf-8"?> 
<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"> 
  <!-- content --> 
  <FrameLayout 
    android:id="@+id/drawer_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/> 
  <!-- Drawer--> 
  <ListView 
    android:id="@+id/drawer_menu"
    android:layout_width="240dp"
    android:layout_height="match_parent"
    android:background="#FFF0F0F0"
    android:layout_gravity="start"/> 
  <!--   
    android:choiceMode    选中状态 跟onItemClick没有冲突  
        none       值为0，表示无选择模式；   
        singleChoice   值为1，表示最多可以有一项被选中；  
        multipleChoice  值为2，表示可以多项被选中。  
    android:layout_gravity left或right left或start  right或end  
      表示在抽屉里的效果是从左到右还是从右到左出现  
  --> 
</android.support.v4.widget.DrawerLayout>

package com.jackie.drawerlayoutdemo; 
import android.os.Bundle; 
import android.support.v4.widget.DrawerLayout; 
import android.support.v7.app.AppCompatActivity; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import android.widget.TextView; 
public class MainActivity extends AppCompatActivity { 
  private String mTitle; 
  private DrawerLayout mDrawerLayout; 
  private ListView mDrawerMenu; 
  @Override
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    initView(); 
    initData(); 
    //默认打开抽屉 
    mDrawerLayout.openDrawer(mDrawerMenu); 
  } 
  private void initView() { 
    mTitle = getResources().getString(R.string.app_name); 
    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout); 
    mDrawerMenu = (ListView) findViewById(R.id.drawer_menu); 
  } 
  private void initData() { 
    //数组定义在xml 文件中 
    String[] items = getResources().getStringArray(R.array.left_drawer_items); 
    ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_expandable_list_item_1); 
    adapter.addAll(items); 
    mDrawerMenu.setAdapter(adapter); 
    mDrawerMenu.setSelection(0); 
    //设置点击item事件 
    mDrawerMenu.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
      @Override
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
        mTitle = ((TextView) view).getText().toString(); 
        switchFragment(); 
        mDrawerLayout.closeDrawer(mDrawerMenu); 
        mDrawerMenu.setSelection(position); 
      } 
    }); 
  } 
  private void switchFragment() { 
    getSupportFragmentManager().beginTransaction().replace(R.id.drawer_container, new ItemFragment(mTitle)).commit(); 
    getSupportActionBar().setTitle(mTitle); 
  } 
}