Buatlah Activity Baru dengan nama Splash_Screen, kemudian buatlah layout untuk activity splash_screen nya, misalnya menambahkan sebuah gambar dan progressbar

package giviews.id.splash;



import android.content.Intent;

import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;



import static android.view.Window.FEATURE_NO_TITLE;



public class Splash_Screen extends AppCompatActivity {



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        this.requestWindowFeature(FEATURE_NO_TITLE);

        setContentView(R.layout.activity_splash__screen);

    Thread myThread = new Thread() {

        @Override

        public void run() {

            try {

                sleep(3000);

                Intent intent = new Intent(getApplicationContext(),MainActivity.class);

                startActivity(intent);

                finish();

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

        }

    };

        myThread.start();

    }

}

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    package="giviews.id.splash">



    <application

        android:allowBackup="true"

        android:icon="@mipmap/ic_launcher"

        android:label="@string/app_name"

        android:roundIcon="@mipmap/ic_launcher_round"

        android:supportsRtl="true"

        android:theme="@style/AppTheme">

        <activity android:name=".Splash_Screen">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />



                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

        <activity

            android:name=".MainActivity"

            android:theme="@style/Base.V7.Theme.AppCompat"

            tools:ignore="DuplicateActivity">

            <meta-data

                android:name="android.support.PARENT_ACTIVITY"

                android:value="giviews.id.splash.MainActivity" />

        </activity>



    </application>



</manifest>

<uses-permission android:name="android.permission.VIBRATE" />

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context="giviews.id.notificationview.NotificationViewActivity">



    <TextView

        android:id="@+id/textView"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Diharapkan Semua Anggota BEM Rapat Di Aula Sekarang..!!"

        tools:layout_editor_absoluteX="9dp"

        tools:layout_editor_absoluteY="16dp" />



</RelativeLayout>

package giviews.id.notificationview;



import android.app.NotificationManager;

import android.app.PendingIntent;

import android.content.Context;

import android.content.Intent;

import android.os.Bundle;

import android.os.Vibrator;

import android.support.v4.app.NotificationCompat;

import android.support.v7.app.AppCompatActivity;

import android.view.View;



public class MainActivity extends AppCompatActivity {

    int notificationID = 1;



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    }



    public void onClick(View view) {

        displayNotification();

    }



    protected void displayNotification()

    {

        //---PendingIntent to launch activity if the user selects

        // this notification---

        Intent i = new Intent(this, NotificationViewActivity.class);

        i.putExtra("notificationID", notificationID);

        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, i, 0);

        NotificationManager nm = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);

        NotificationCompat.Builder notifBuilder;

        notifBuilder = new NotificationCompat.Builder(this)

                .setSmallIcon(R.drawable.gbrnotif)

                .setContentTitle("Ada Meeting BEM Sekarang...!")

                .setContentText("Reminder: Rapat Akan Mulai 5 minutes")

                .setContentIntent(pendingIntent)

                .addAction(R.mipmap.ic_launcher,"Read More",pendingIntent);



        Vibrator vi;

        vi=(Vibrator) getSystemService(Context.VIBRATOR_SERVICE);

        if (vi.hasVibrator()){

            vi.vibrate(20000);

        }

        nm.notify(notificationID, notifBuilder.build());

    }

}

package giviews.id.notificationview;



import android.app.NotificationManager;

import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;



public class NotificationViewActivity extends AppCompatActivity {



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_notification_view);



        //---look up the notification manager service---

        NotificationManager nm = (NotificationManager)

                getSystemService(NOTIFICATION_SERVICE);

        //---cancel the notification that we started---

        nm.cancel(getIntent().getExtras().getInt("notificationID"));

    }

}

Langkah Pertama buatlah button untuk memanggil alert dialognya

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical" android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:padding="5dp">



    <TextView

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_gravity="center"

        android:text="@string/login"

        android:id="@+id/lblLogin"

        android:textSize="25sp"

        android:layout_marginTop="5dp"

        android:textStyle="bold"/>



    <EditText

        android:id="@+id/etEmail"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:ems="10"

        android:layout_marginTop="10dp"

        android:inputType="textEmailAddress"

        android:hint="@string/email" />



    <EditText

        android:id="@+id/etPass"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:ems="10"

        android:layout_marginTop="5dp"

        android:hint="@string/password"

        android:inputType="textPassword" />



    <Button

        android:id="@+id/btnLogin"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="@string/login_label"

        android:background="@color/colorAccent"

        android:textColor="@android:color/white"

        android:layout_marginTop="10dp"/>





</LinearLayout>

package giviews.id.customalertdialog;



import android.support.v7.app.AlertDialog;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.Toast;



public class MainActivity extends AppCompatActivity {



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);



        Button mShowDialog = (Button) findViewById(R.id.btnShowDialog);

        mShowDialog.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                AlertDialog.Builder mBuilder = new AlertDialog.Builder(MainActivity.this);

                View mView = getLayoutInflater().inflate(R.layout.dialog_login, null);

                final EditText mEmail = (EditText) mView.findViewById(R.id.etEmail);

                final EditText mPass = (EditText) mView.findViewById(R.id.etPass);

                Button mLogin = (Button) mView.findViewById(R.id.btnLogin);



                mLogin.setOnClickListener(new View.OnClickListener() {

                    @Override

                    public void onClick(View v) {

                        if (!mEmail.getText().toString().isEmpty() && !mPass.getText().toString().isEmpty()) {

                            Toast.makeText(MainActivity.this,

                                    R.string.login_success,

                                    Toast.LENGTH_SHORT).show();

                        }else{

                            Toast.makeText(MainActivity.this,

                                    R.string.login_error_msg,

                                    Toast.LENGTH_SHORT).show();

                        }

                    }

                });

                mBuilder.setView(mView);

                AlertDialog dialog = mBuilder.create();

                dialog.show();

            }

        });

    }

}