public class MessageContentObserver extends ContentObserver {
  private Context mContext; 
  private Handler mHandler; 
  private String code; 
  public MessageContentObserver(Context context, Handler handler) {    
    super(handler);
    mContext = context;
    mHandler = handler;
  }  
  /**
   * 回调函数, 当监听的Uri发生改变时，会回调该方法
   * 需要注意的是当收到短信的时候会回调两次
   * 收到短信一般来说都是执行了两次onchange方法.第一次一般都是raw的这个.
   * 虽然收到了短信.但是短信并没有写入到收件箱里
   */
  @Override
  public void onChange(boolean selfChange, Uri uri) {   
    if (uri.toString().equals("content://sms/raw")) {     
     return;
    }    
   Uri inboxUri = Uri.parse("content://sms/inbox");   
   Cursor c = mContext.getContentResolver().query(inboxUri, null, null, null, "date desc"); // 按时间顺序排序短信数据库
    if (c != null) {      
       if (c.moveToFirst()) {       
         String address = c.getString(c.getColumnIndex("address"));//发送方号码
         String body = c.getString(c.getColumnIndex("body")); // 短信内容
        if (!address.equals("10086")) {      
            return;
        }        
        Pattern pattern = Pattern.compile("(\\d{6})");//正则表达式匹配验证码
        Matcher matcher = pattern.matcher(body);        if (matcher.find()) {
          code = matcher.group(0);          
          Message msg = Message.obtain();
          msg.what = MainActivity.MSG_RECEIVE_CODE;
          msg.obj = code;
          mHandler.sendMessage(msg);
        }
      }
      c.close();
    }
  }
}

/**
 * 短信验证码自动填写功能的实现
 */
public class MainActivity extends Activity { 
  public static final int MSG_RECEIVE_CODE = 1; //收到短信的验证码
  private EditText codeEdt; //短信验证码的输入框
  private MessageContentObserver messageContentObserver;  //回调接口
  @SuppressLint("HandlerLeak")
  Handler handler = new Handler() {    
  @Override
  public void handleMessage(Message msg) {   
   if (msg.what == MSG_RECEIVE_CODE) {
       //设置读取到的内容
      }
    }
  };  
  @Override
  protected void onCreate(Bundle savedInstanceState) {   
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    codeEdt = (EditText) findViewById(R.id.smsCode);
    findViewById(R.id.send_sms_btn).setOnClickListener(new View.OnClickListener() {    
      @Override
      public void onClick(View v) {
        senSMSCode();
      }
    });
    messageContentObserver = new MessageContentObserver(MainActivity.this, handler);
 getContentResolver().registerContentObserver(Uri.parse("content://sms/"), true, messageContentObserver);
  }  
   /**
   * 取消注册
   */
  @Override
  protected void onDestroy() {   
    super.onDestroy();
 getContentResolver().unregisterContentObserver(messageContentObserver);
  }  
  private void senSMSCode() {
  }
}

<!--读取短信的权限-->
  <uses-permission android:name="android.permission.RECEIVE_SMS"/>
  <uses-permission android:name="android.permission.READ_SMS" />