Tutorial 2: Understanding Android Layouts

In Android, there are various types of layouts available which are used to design the screen or we can say, are used to arrange the order of various widgets(like- TextView, EditText, Button, Image, ImageButton etc.) in the required manner. In Android terms, the layouts are called as ViewGroups and widgets are called as Views.

The wise use of different layouts in the screen can reduce the development time and effort and even can save you from the later stage issues (like- inserting more widgets in the screen in later stage, porting to different screen resolutions, we will discuss it in the upcoming posts).

So, Lets start understanding the behavior of different layouts:

Linear Layout: Linear layout arranges all the children widgets in one direction like- vertical or horizontal as shown in the image.

So, where ever we want some widgets to be aligned in a single direction, we can make use of Linear Layout.

Remember that designing the android screen goes from top to down fashion.

Android has given three amazing properties- wrap_content, match_parent, fill_parent to declare the height and width of the layouts and widgets. The one should make use of them very wisely. Never practice declaring the absolute height and width of any view. The best way is to use property wrap_content maximally.

Relative Layout: Relative layout arranges the children widgets relative to the parent layout or relative to each other. Best way to understand it, look at the image.

Table Layout: Table layout arranges the children widgets in the table, i.e. rows and columns, look at the image.

Frame Layout: Frame layout arranges the children widgets relative to top left point. In this way, the widgets may get overlapped as shown in the image.

Absolute Layout: Absolute layout pins the children widgets in the coordinate points as shown in the image.

However, this layout is advised not to practice as it raises the issues while designing the same layout for different screen resolutions. Even it has been deprecated in the latest versions of Android.

Please post your feedbacks/challenges J

Tutorial 1: Login Screen

Hi guys!! Here we open the Android tutorial series with Login Screen tutorials.

Tuts Approach: Initially we will start learning Android UI creation and implementing small logic on them or you can say various events on widgets(like- OnClick, OnTouch etc.)

Requirement: A login screen which will accept a valid username and password

Implementation:

• Select Eclipse->File->New->Android Project, in the dialog, fill the fields, Project Name (ex: LoginExample), Build Target (to compile the application by a particular Android SDK), Application Name (name of application, ex: LoginExample), Package Name (ex: com.deepak.login), Create Activity (ex: LoginActivity)
• Click on Next->Finish. An android project folder with name ‘LoginExample’ will get built in the left pane (Project Explorer) of Eclipse.
• On exploring the Project folder, you will be able to see the sub folders /src, /gen, /res & AndroidManifest.xml 

Note: The above steps are for project creation which will not be mentioned in the each post. Please learn and practice them.

Creating Layout: After the deciding the screen design by some doing paper work or on paint file, we should create the layout first. Here, in our case, I am not showing any raw paper work or paint file for screen design. Once you will go through this layout till the end, you will get the idea for screen designing.

Source code:

In res/values folder in the project in your eclipse, edit strings.xml file

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

<resources>

    <string name="hello">Hello World, LoginActivity!</string>

    <string name="app_name">LoginExample</string>

      <string name="login_title">Login Screen</string>

      <string name="username">Username</string>

      <string name="password">Password</string>

      <string name="login">Login</string>

</resources>

In the string.xml file, we should declare all Strings which are going to use in the screen, so that we need not to hard code them in the Java code.

Place the login.xml file in res/layout/ folder in the project in your eclipse

Layout File : login.xml

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

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

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical" >

      <!-- Login Title -->

    <TextView

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="@string/login_title"

        android:gravity="center_horizontal"

        android:textSize="20dp" 

        />

    <!-- Login Image -->

    <ImageView

        android:layout_width="fill_parent"

        android:layout_height="0dp"

        android:gravity="center_horizontal"

        android:src="@drawable/ic_launcher"

        android:layout_weight="1.1"

        android:padding="20dp"

        />

    <!-- layout for Username -->

    <LinearLayout

            android:layout_width="fill_parent"

      android:layout_height="wrap_content"

      android:orientation="horizontal"

      android:layout_weight="0.01"

      android:padding="10dp">

     

        <TextView

            android:layout_height="wrap_content"

            android:layout_width="0dp"

            android:layout_weight="1.0"

            android:text="@string/username"

            android:textSize="18dp"

            />

        <EditText

            android:id="@+id/username"

            android:layout_width="0dp"

            android:layout_height="wrap_content"

            android:layout_weight="1.0"

            android:ems="10"

            android:inputType="text" >

            <requestFocus />

        </EditText>

    </LinearLayout>

    <!-- layout for Password -->

    <LinearLayout

            android:layout_width="fill_parent"

      android:layout_height="wrap_content"

      android:orientation="horizontal"

      android:layout_weight="0.01"

      android:padding="10dp"

      >

        <TextView

            android:layout_height="wrap_content"

            android:layout_width="0dp"

            android:layout_weight="1.0"

            android:text="@string/password"

            android:textSize="18dp"

            />

        <EditText

            android:id="@+id/password"

            android:layout_height="wrap_content"

            android:layout_width="0dp"

            android:layout_weight="1.0"

            android:inputType="textPassword"

            />

    </LinearLayout>

    <Button

        android:id="@+id/login"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="@string/login"

        android:layout_margin="10dp"

        />

</LinearLayout>

In the above layout, the widgets which we have used are TextView (Title Label for the screen), ImageView (Image for the Screen), Linear layout (for username TextView i.e. label and EditText i.e. textbox), another Linear Layout (for password TextView i.e. label and EditText i.e. textbox) and a button (for Login).

We have written the properties to each of these widgets like-id, width, height, text, textsize, padding, margin etc.

For more in-depth knowledge on UI elements: Follow this links

http://developer.android.com/guide/topics/ui/index.html

http://developer.android.com/guide/topics/ui/declaring-layout.html

Writing Activity Class: Now, we gotta write Activity class which will contain the business logic. In Activity class, we will bind the UI elements (which we have written in the layout xml file) in the form of Java Class objects and perform action/events like getting inputs from user, performing operation on the data and responding or doing action based on that.

Edit the file from src/com.deepak.login/LoginActivity.java from your Eclipse

Source code: LoginActivity.java

package com.deepak.login;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;

import android.widget.Toast;

public class LoginActivity extends Activity {

      String userName, passWord;

      EditText username, password;

      Button login;    

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.login);

        // UI elements gets bind in form of Java Objects

        username = (EditText)findViewById(R.id.username);

        password = (EditText)findViewById(R.id.password);

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

        // now we have got the handle over the UI widgets

        // setting listener on Login Button

        // i.e. OnClick Event

        login.setOnClickListener(loginListener);  

    }

    private OnClickListener loginListener = new OnClickListener() {

      public void onClick(View v) {

//getting inputs from user and performing data operations

                   

            if(username.getText().toString().equals("deepak") &&

                        password.getText().toString().equals("garg")){

// responding to the User inputs

                  Toast.makeText(getApplicationContext(), "Login Successfully !!!", Toast.LENGTH_LONG).show();      

            }else

                  Toast.makeText(getApplicationContext(), "Login Not Successful !!!", Toast.LENGTH_LONG).show();                           

      }

    };

}

Output: 

Congs for creating the first screen on android, the login screen. Guys! This tutorial gives you the basic look on android development.

Android recommends the Login Design in a different way:

The above design is the typical Login screen design which we see on all desktop applications or even on some mobile apps. Now, we will implement the login design what Android recommends. We can make some changes in the earlier design to reach to the new one; the new one is more specific to mobile screens.

Create a new layout xml file the login_android.xml file in res/layout/ folder in the project in your eclipse

Source code: login_android.xml

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

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

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical" >

      <!-- Login Title -->

    <TextView

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="@string/login_title"

        android:gravity="center_horizontal"

        android:textSize="20dp" 

        />

    <!-- Login Image -->

    <ImageView

        android:layout_width="fill_parent"

        android:layout_height="0dp"

        android:gravity="center_horizontal"

        android:src="@drawable/ic_launcher"

        android:layout_weight="1.1"

        android:padding="20dp"

        />

    <!-- layout for Username -->

    <LinearLayout

            android:layout_width="fill_parent"

      android:layout_height="wrap_content"

      android:orientation="horizontal"

      android:layout_weight="0.01"

      android:padding="10dp">

        <EditText

            android:id="@+id/username"

            android:layout_width="0dp"

            android:layout_height="wrap_content"

            android:layout_weight="1.0"

            android:ems="10"

            android:inputType="text"

            android:hint="@string/username"

            >

            <requestFocus />

        </EditText>

    </LinearLayout>

    <!-- layout for Password -->

    <LinearLayout

            android:layout_width="fill_parent"

      android:layout_height="wrap_content"

      android:orientation="horizontal"

      android:layout_weight="0.01"

      android:padding="10dp"

     

      >

        <EditText

            android:id="@+id/password"

            android:layout_height="wrap_content"

            android:layout_width="0dp"

            android:layout_weight="1.0"

            android:inputType="textPassword"

            android:hint="@string/password"

            />

    </LinearLayout>

    <Button

        android:id="@+id/login"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="@string/login"

        android:layout_margin="10dp"

        />

</LinearLayout>

Activity: Now we just need to set this layout file instead of the earlier one, so a small change in Activity class.

In the onCreate() function

setContentView(R.layout.login_android);

Output: 

In the output screen, We have removed the Labels for username and password, instead of this, we have provided hints with in the respective fields and even user can type long username or password.

Please post your feedbacks/challenges J