需要实现如下效果：

首先定义一个SMSContentObserver 来拦截短信内容：

package “你的包名”;

import android.content.Context;
import android.database.ContentObserver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Handler;
import android.text.TextUtils;
import android.util.Log;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class SMSContentObserver extends ContentObserver {
    private static String TAG = "SMSContentObserver";
    private String patternCoder = "\\d{4}";     //正则表达式 取4位数
    private String strContent;                  //验证码内容
    private Context mContext  ;
    private Handler mHandler ;   				  //更新UI线程

    private String TELPHONE = "TMRTXMIN"; // 短信来源号码
    private String TelPHONECONTEXT ="iViralLink"; // 短信内容 特殊关键字

    //    8448631136
    public SMSContentObserver(Context context, Handler handler) {
        super(handler);
        mContext = context ;
        mHandler = handler ;
    }
    /**
     * 当所监听的Uri发生改变时，就会回调此方法
     *
     * @param selfChange  此值意义不大 一般情况下该回调值false
     */
    @Override
    public void onChange(boolean selfChange){
        Log.i(TAG, "the sms table has changed");
        //查询收件箱里的内容
        Uri outSMSUri = Uri.parse("content://sms/inbox") ;
        Cursor c = mContext.getContentResolver().query(outSMSUri, null, null, null,"date desc");
        if(c != null){
            Log.i(TAG, "the number of send is "+c.getCount()) ;
            StringBuilder sb = new StringBuilder() ;
            c.moveToNext();
            String message = c.getString(c.getColumnIndex("body"));      // 短信内容
            String phone = c.getString(c.getColumnIndex("address"));	   //短信来源号码
            Log.i(TAG,"message : "+message);
            Log.i(TAG,"phone : "+phone);
            c.close();
//            if(checkPhone(phone) &&checkString(message)){ //指定号码 指定字符串匹配
                String code = patternCode(message);
                assert code != null;
                if(!TextUtils.isEmpty(code) ){
                    strContent = code;
                }
                mHandler.obtainMessage(1, sb.toString()).sendToTarget();
//            }
        }
    }

    //指定一个号码，只读取与他有关的新消息。
    private boolean checkPhone(String phone) {
        // TODO Auto-generated method stub
        String c_phone = TELPHONE;
        if(c_phone.equals(phone) )
            return true;
        return false;
    }

    //指定一关键字符串，用来确认短信内容是我们想要去提取的
    private boolean checkString(String message){
        if(TextUtils.isEmpty(message))
            return false;
        Pattern p = Pattern.compile(TelPHONECONTEXT);          //这个关键字符串可以自定义
        Matcher matcher = p.matcher(message);
        if(matcher.find())
            return true;
        return false;
    }
    //匹配短信中的数字（验证码）
    private String patternCode(String patternContent){
        if(TextUtils.isEmpty(patternContent))
            return null;
        Pattern p = Pattern.compile(patternCoder);
        Matcher matcher = p.matcher(patternContent);
        if(matcher.find())
            return matcher.group();
        return null;
    }
    public String getStrContent(){
        return strContent;
    }
}

然后在需要的地方调用：

    private SMSContentObserver smsContentObserver;
    private Handler mHandler = new Handler() {
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case 1:
                    String outbox = smsContentObserver.getStrContent();//(String) msg.obj;  验证码内容    
//                    et_code.setText(outbox);   //直接把验证码输入到指定输入框
                    break;
                default:
                    break;
            }
        }
    };


    private void initRegisterContentObserver() {
        smsContentObserver = new SMSContentObserver(this, mHandler);
        Uri smsUri = Uri.parse("content://sms");
        getContentResolver().registerContentObserver(smsUri, true, smsContentObserver);
    }


    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (getContentResolver()!=null){
            getContentResolver().unregisterContentObserver(smsContentObserver);
        }
    }



    @Override
    protected int getLayoutId() {
        return R.layout.act_register;
    }

    @Override
    protected void onCreate(@Nullable Bundle bundle) {
        super.onCreate(bundle);

        initRegisterContentObserver();   //初始化smsContentObserver 拦截验证码
    }

需要注意，edittext的inputstyle需要设置为number：

   <EditText
                android:id="@+id/et_code"
                android:layout_width="match_parent"
                android:layout_height="@dimen/dp30"
                android:background="@null"
                android:layout_centerVertical="true"
                android:layout_toRightOf="@+id/iv_code"
                android:lines="1"
                android:textSize="@dimen/sp14"
                android:hint="请输入验证码"
                android:textColorHint="#999"
                android:textColor="#fff"
                android:inputType="number"
                android:layout_toLeftOf="@+id/tv_get_code"
                android:layout_marginRight="@dimen/dp10"
                />

最后就是在获取短信权限，这个属于危险权限，需要动态获取：

   
 @Override
    protected void onCreate(@Nullable Bundle bundle) {
        super.onCreate(bundle);
      
        if(!checkPermission()) if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.M){
            requestPermissions(PS, PS.hashCode());
        }

   
        initRegisterContentObserver();
    }





public void onRequestPermissionsResult(int req, @NonNull String[] ps, @NonNull int[] res){
        if(req==PS.hashCode()){
            if(!checkPermission()) getProxy().alert("定位权限不足，请检查手机设置");
            return;
        }
        super.onRequestPermissionsResult(req, ps, res);
    }

    boolean checkPermission(){
        boolean ok=true;
        for(String p: PS){
            ok=checkCallingOrSelfPermission(p)== PackageManager.PERMISSION_GRANTED;
            if(!ok) break;
        }
        if(!ok) return false;
       
        return true;
    }

    static final String[] PS={
//            Manifest.permission.ACCESS_FINE_LOCATION,    //定位
//            Manifest.permission.WRITE_EXTERNAL_STORAGE, //SD卡写入
      
            Manifest.permission.READ_SMS,
            Manifest.permission.RECEIVE_SMS
    };

实际完成实现的效果如下：

完成~