android studio 横幅,有关 android studio notification 横幅弹出的功能没有反应

小妹在这里已经卡了2-3天了，研究了很多人的文章，

除了低版本api 17有成功外，其他的不是channel null 就是没反应 (channel null已解决)

拜托各位大大，帮小妹一下，以下是我的程式跟 gradle, 我在这里卡好久又没有人可问(哭)

public class MainActivity extends AppCompatActivity implements View.OnClickListener

{

private Context mContext;

private NotificationManager mNManager;

private Notification notify1;

Bitmap LargeBitmap = null;

private static final int NOTIFYID_1 = 1;

private NotificationCompat.Builder builder;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mContext = MainActivity.this;

LargeBitmap = BitmapFactory.decodeResource(getResources(),R.drawable.app_icon_128x128);

mNManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

Button btn_pop_no = (Button) findViewById(R.id.btn_pop_no);

Button btn_clear_no = (Button) findViewById(R.id.btn_clear_no);

NotificationCompat.Builder builder;

}

@Override

public void onClick(View v) {

Log.i("VERION", "onClick: "+ Build.VERSION.SDK_INT);

switch (v.getId()) {

case R.id.btn_pop_no:

if(Build.VERSION.SDK_INT >=26) {

NotificationChannel notificationChannel = new NotificationChannel("braun","braun",NotificationManager.IMPORTANCE_DEFAULT);

mNManager.createNotificationChannel(notificationChannel);

builder = new NotificationCompat.Builder(this,"braun");

}

else {

builder = new NotificationCompat.Builder(this);

}

Intent intent = new Intent(mContext,NotifyDetailActivity.class);

PendingIntent pit = PendingIntent.getActivity(mContext,100,intent,PendingIntent.FLAG_UPDATE_CUR RENT);

builder.setContentTitle("簡單教程").setSubText("簡單教程，簡單編程").setTicker("簡單教程上線啦....")

.setWhen(System.currentTimeMillis())

.setSmallIcon(R.drawable.app_icon_32x32)

.setLargeIcon(LargeBitmap)

.setDefaults(Notification.DEFAULT_LIGHTS | Notification.DEFAULT_VIBRATE)

.setSound(Uri.parse("android.resource://"+getPackageName() +"/"+R.raw.sms))

.setFullScreenIntent(pit,true)

.setAutoCancel(true)

.setContentIntent(pit);

notify1 = builder.build();

mNManager.notify(NOTIFYID_1,notify1);

break; case R.id.btn_clear_no:

mNManager.cancel(NOTIFYID_1);

break; }

}

}