Create login application where you will have to validate username and passwords Till the username and password is not validated , login button should remain disabled.

Activity_Main.xml:

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

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

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity" >

    <TextView

        android:id="@+id/textView1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentLeft="true"

        android:layout_alignParentTop="true"

        android:layout_marginTop="56dp"

        android:text="@string/Username"

        android:textAppearance="?android:attr/textAppearanceMedium" />

    <EditText

        android:id="@+id/editText1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignBottom="@+id/textView1"

        android:layout_alignParentRight="true"

        android:ems="10"

        android:inputType="text" />

    <TextView

        android:id="@+id/textView2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignRight="@+id/textView1"

        android:layout_below="@+id/textView1"

        android:layout_marginTop="48dp"

        android:text="@string/Password"

        android:textAppearance="?android:attr/textAppearanceMedium" />

    <EditText

        android:id="@+id/editText2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignBaseline="@+id/textView2"

        android:layout_alignBottom="@+id/textView2"

        android:layout_alignLeft="@+id/editText1"

        android:ems="10"

        android:inputType="textPassword" >

        <requestFocus />

    </EditText>

    <Button

        android:id="@+id/button1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/editText2"

        android:layout_marginTop="68dp"

        android:layout_toLeftOf="@+id/editText2"

        android:text="@string/Login" />

    <Button

        android:id="@+id/button2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignBaseline="@+id/button1"

        android:layout_alignBottom="@+id/button1"

        android:layout_alignLeft="@+id/editText2"

        android:layout_marginLeft="42dp"

        android:text="@string/Cancel"/>

</RelativeLayout>

MainActivity.java

package com.example.loginform;

import com.example.loginform.R;

import android.os.Bundle;

import android.annotation.SuppressLint;

import android.app.Activity;

import android.text.Editable;

import android.text.TextWatcher;

import android.view.*;

import android.view.View.OnClickListener;

import android.widget.*;

public class MainActivity extends Activity implements OnClickListener,TextWatcher{

           

            EditText name;

            EditText pass;

            Button login;

            Button cancel;

           

           

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        name=(EditText )findViewById(R.id.editText1);

        name.addTextChangedListener(this);

        pass=(EditText )findViewById(R.id.editText2);

        pass.addTextChangedListener(this);

        login=(Button )findViewById(R.id.button1);

        cancel=(Button )findViewById(R.id.button2);

        login.setOnClickListener(this);

        cancel.setOnClickListener(this);

        login.setEnabled(false);

        cancel.setEnabled(true);

    }

    @Override

    public boolean onCreateOptionsMenu(Menu menu) {

       

        getMenuInflater().inflate(R.menu.activity_main, menu);

        return true;

    }

            @SuppressLint("ShowToast") @Override

            public void onClick(View v) {

                                                                                               

            }

            public void afterTextChanged(Editable arg0) {

                       

                       

            }

            public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,int arg3) {

                       

                       

            }

            public void onTextChanged(CharSequence arg0, int arg1, int arg2, int arg3) {

                       

                        String na=name.getText().toString();

                        String pa=pass.getText().toString();

                       

                        if(na.equals("chaitu") && pa.equals("root")) 

                        {

                                    Button btn = (Button) findViewById(R.id.button1);

                                    btn.setEnabled(true);

                        }

            }

   }