107-Creating Second Activity

In this lesson, you’ll add some code to MainActivitythat starts a new activity when the user clicks the Send button.

(This tutorial is based on http://developer.android.com/training/basics/firstapp/starting-activity.html )

1) Run ADT and open My First App project

Create a new project MyFirstApp.

Download MyFirstApp Project here:

2) Add a Java Method Call to Send Button

To respond to the button's on-click event, add the android:onClick attribute to the <Button> element in the layout file.

<LinearLayout 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:orientation="horizontal"

tools:context=".MainActivity" >

<EditText

android:layout_weight="1"

android:layout_width="0dp"

android:layout_height="wrap_content"

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

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/button_send"

android:onClick="sendMessage" />

</LinearLayout>

3) Add a Java Method to MainActivity Class

package com.example.myfirstapp;

import android.os.Bundle;

import android.app.Activity;

import android.util.Log;

import android.view.Menu;

import android.view.View;

public class MainActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

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

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

return true;

}

/** Called when the user clicks the Send button */

public void sendMessage(View view) {

// Do something in response to button

Log.v("Click","Send Button is clicked");

}

You need to import the following classes…

import android.util.Log;

import android.view.View;

4) Run and Observe LogCat Window

5) Create a Second Activity

5.1) Go to menu. Select File/New/Other… (since Android Activity is not listed in menu)

5.2) In the New Dialog Window, Select Android/Android Activity.

5.3) Choose Blank Activity

5.4) Type the name DisplayMessageActivity

Click Finish.

6) Pass the control from MainActivity to SecondActivity

Edit MainActivity by adding an Intent Object and a method call “startActivity”.

package com.example.myfirstapp;

import android.os.Bundle;

import android.app.Activity;

import android.util.Log;

import android.view.Menu;

import android.view.View;

public class MainActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

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

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

return true;

}

/** Called when the user clicks the Send button */

public void sendMessage(View view) {

// Do something in response to button

Log.v("Click","Send Button is clicked");

Intent intent = new Intent(this, DisplayMessageActivity.class);

startActivity(intent);

}

You need to import the following classes…

import android.content.Intent;

7) Capture string input and pass to Second Activity

7.1) Give an id to the EditText object

edit the layout by giving the id property to EditText.

<LinearLayout 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:orientation="horizontal"

tools:context=".MainActivity" >

<EditText

android:id="@+id/edit_message"

android:layout_weight="1"

android:layout_width="0dp"

android:layout_height="wrap_content"

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

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/button_send"

android:onClick="sendMessage" />

</LinearLayout>

7.2) Update the MainActivity Class to capture input and pass to intent object.

package com.example.myfirstapp;

import android.os.Bundle;

import android.app.Activity;

import android.content.Intent;

import android.util.Log;

import android.view.Menu;

import android.view.View;

public class MainActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

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

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

return true;

}

/** Called when the user clicks the Send button */

public void sendMessage(View view) {

// Do something in response to button

Log.v("Click","Send Button is clicked");

Intent intent = new Intent(this, DisplayMessageActivity.class);

EditText editText = (EditText) findViewById(R.id.edit_message);

String message = editText.getText().toString();

intent.putExtra(EXTRA_MESSAGE, message);

startActivity(intent);

}

You need to…

1) import android.widget.EditText;

2) Add a public static final String constant

public static final String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";

example:

public=it is accessible from outside of class

final=it cannot be changed

static=it will be created once and therefore doesn’t require instantiation.

The startActivity call can be written as a single line statement as follows

startActivity(new Intent(this, DisplayMessageActivity.class));

8) Update DisplayMessageActivity Class

package com.example.myfirstapp;

import android.os.Bundle;

import android.app.Activity;

import android.content.Intent;

import android.view.Menu;

import android.widget.TextView;

public class DisplayMessageActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_display_message);

// Get the message from the intent

Intent intent = getIntent();

String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

// Create the text view

TextView textView = new TextView(this);

textView.setTextSize(40);

textView.setText(message);

// Set the text view as the activity layout

setContentView(textView);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

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

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

return true;

}

You need to…

1) import android.content.Intent;

2) import android.widget.TextView;

9) Run

DOWNLOAD

107MyFirstApp.zip