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();

            }

        });

    }

}