How to Use Switching Between Activities and Adding Images in an Android App

Chhavi Goel
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Introduction

Today you are going to learn how to create a simple Metro Map app. This app is being created just to show you how to switch among various activities and how to add an image in Android programming.

I used Android studio to make this app since we can preview the layout any time easily in it. You can use any other IDE like Eclipse.

Step 1:

Open the layout XML file (in my case activity_main.xml) present in the layout folder of your project. Initially you will get the following code:

<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"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

android:paddingBottom="@dimen/activity_vertical_margin"

tools:context=".MainActivity">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

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

</RelativeLayout>

Step 2:

Do the following changes in your layout file (I am changing the RealtiveLayout to LinearLayout because my layout just exists so my final view of the layout does not require any relative placing of components).

Step 3:

Now let us create the buttons in the XML file as required in this app:

<Button

android:id="@+id/fullMap"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/full"

android:textColor="@color/fullCol"

android:background="@color/bg"

<Button

android:id="@+id/redMap"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/red"

android:textColor="@color/redCol"

<Button

android:id="@+id/blueMap"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/blue"

android:textColor="@color/blueCol"

<Button

android:id="@+id/greenMap"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/green"

android:textColor="@color/greenCol"

<Button

android:id="@+id/orangeMap"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/orange"

android:textColor="@color/orangeCol"

Step 4:

The changes in "string.xml" file in the "values" folder are:

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

<string name="action_settings">Settings</string>

<string name="hello_world">Welcome to metro maps.......</string>

<string name="green">Green Line Map</string>

<string name="orange">Orange Line Map</string>

</resources>

Step 5:

Since I wanted to change the text colors in the Buttons to make the layout more appealing, let us create a "colors.xml" file. Right-click on Values then select "New" -> "Values Resource File". The contents of this file are:

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

</resources>

Note the use of reference of the colors created above in the layout's XML file.

Finally the layout looks like:

Step 6:

Let us create another layout file to make the layout of the page displaying the image. Right-click on Layout then select "New" -> "Values Resource File". Name it as "activity_fullmap". The contents of this file are:

<Button

android:id="@+id/back"

android:layout_width="100dp"

android:layout_height="50dp"

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

<ImageView

android:id="@+id/im"

android:layout_height="410dp"

android:layout_width="350dp"

android:layout_marginTop="50dp"

android:layout_marginLeft="20dp"

ImageView has been added for the display of the image of the Metro Maps.

Note: The name of the new XML file must contain an underscore, otherwise it will show you an error in the later stages of project completion.

This will look like:

Step 7:

Download all the images required from Google, in other words the images of the Metro Maps. I have used a Metro full map, Blue Line map, Red Line map, Green Line map and Orange Line map. Copy these jpeg images and paste them in "drawable". You can paste these images in all the drawables like drawable-hdpi, drawable-ldpi etc to have a view in all sizes. The names of the image files used by me are: blue, red, green, orange, full.

Now let us start with the Java coding....

Step 8:

Make a new activity namely "FulllMap.java" to display the complete map of Metro. Right-click on "src" then select "Java Class". Name this class "FullMap". The contents of this file is:

package com.metro;

import android.app.Activity;

import android.content.Context;

import android.content.Intent;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.ImageView;

public class FullMap extends Activity

{

ImageView v; // to be able to display the image

Button b;

final Context context=this;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_fullmap); // note the use of the layout file

v=(ImageView)findViewById(R.id.im);

v.setImageResource(R.drawable.full); //setting the required inage of full map

b=(Button)findViewById(R.id.back); // button created to go to the front page

b.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

Intent i=new Intent(context,MainActivity.class); /*intent of the main activity is set so as to return to the main page*/

startActivity(i);

}

});

}

Step 9:

Similarly make activities for the remaining maps to be displayed. So make 4 more activities in the same way and name them "RedMap", "BlueMap", "GreenMap", "OrangeMap". The code remains the same as above except the name of the image file to be opened. Also the package has to be the same.

In RedMap.java: v.setImageResource(R.drawable.red);

In BlueMap.java: v.setImageResource(R.drawable.blue);

In GreenMap.java: v.setImageResource(R.drawable.green);

In OrangeMap.java: v.setImageResource(R.drawable.orange);

Rest of the code remains same as that of FullMap.java

Step10:

Make the changes in "MainActivity.java" (created by default) in "src" as follows:

package com.metro;

import android.content.Context;

import android.content.Intent;

import android.os.Bundle;

import android.app.Activity;

import android.view.Menu;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.ImageView;

public class MainActivity extends Activity implements OnClickListener {

ImageView image;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

((Button)findViewById(R.id.fullMap)).setOnClickListener(this);

((Button)findViewById(R.id.redMap)).setOnClickListener(this);

((Button)findViewById(R.id.blueMap)).setOnClickListener(this);

((Button)findViewById(R.id.greenMap)).setOnClickListener(this);

((Button)findViewById(R.id.orangeMap)).setOnClickListener(this);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

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

return true;

}

@Override

//this method will be called on button click

public void onClick(View v) {

// TODO Auto-generated method stub

final Context context=this;

switch(v.getId())

{

//when the button for red map is pressed, open the RedMap activity

case R.id.redMap:

Intent i=new Intent(context,RedMap.class);

startActivity(i);

break;

//when the button for blue map is pressed, open the BlueMap activity

case R.id.blueMap:

Intent i1=new Intent(context,BlueMap.class);

startActivity(i1);

break;

//when the button for green map is pressed, open the GreenMap activity

case R.id.greenMap:

Intent i2=new Intent(context,GreenMap.class);

startActivity(i2);

break;

//when the button for orange map is pressed, open the OrangeMap activity

case R.id.orangeMap:

Intent i3=new Intent(context,OrangeMap.class);

startActivity(i3);

break;

//when the button for full map is pressed, open the FullMap activity

case R.id.fullMap:

Intent i4=new Intent(context,FullMap.class);

startActivity(i4);

break;

}

Step 11:

Don't forget to make changes in the Manifest file, otherwise the new activities will not run. Open the manifest file "AndroidManifest.xml" (in my case). Initially you will see the following code:

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

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

package="com.metro"

android:versionCode="1"

android:versionName="1.0" >

<uses-sdk

android:minSdkVersion="8"

android:targetSdkVersion="17" />

<application

android:allowBackup="true"

android:icon="@drawable/ic_launcher"

android:label="@string/app_name"

android:theme="@style/AppTheme" >

<activity

android:name="com.metro.MainActivity"

android:label="@string/app_name" >

<intent-filter>

</intent-filter>

</activity>

</application>

</manifest>

Now make the following changes in this file to add other activities: ( write this between the closing tag of the acivity and application in the preceding shown file)

<activity

android:name="com.metro.BlueMap"

android:label="metro">

</activity>

<activity

android:name="com.metro.RedMap"

android:label="metro">

</activity>

<activity

android:name="com.metro.GreenMap"

android:label="metro">

</activity>

<activity

android:name="com.metro.OrangeMap"

android:label="metro">

</activity>

<activity

android:name="com.metro.FullMap"

android:label="metro">

</activity>

Step 12:

Now your Metro app is ready to run.

On running the first screen looks like:

When you click on the Full Map button, you will get:

You can click on other buttons and see the output.

Thank you... enjoy coding :)

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