【Android Development for Beginners】 Lesson 2A : Do Something When Button is Clicked

This Notes is according to the udacity free course :

Android Development for Beginners

Lesson 2A : 
Do Something When Button is Clicked

We finish the layouts arrangement and we start to enter the most important step which is let your app can interact with users.



1. Activity : What's activity in android app?
When we build up an application, you may notice when we choose "empty activity" or " blank activity", and click into the windows show what's the activity name for this layout.

Activity represent single focus thing that user can do.

There are some examples :

The Gmail app shows 2 activities that we can do in the app and one activity only do one thing.

So as this app we will do in the future project, and we can find out that one activity just like one layer only can do one thing.

We have one activity in our Justjava app.

If we want the app to do something we have to open our java file in this project.
Follow the steps and here it is.

Don't be afraid that all codes, we will learn more in the future class.

First DELETE all the codes in .java file and replace them by the new codes below :

	package com.example.android.justjava;
	import android.os.Bundle;
	import android.support.v7.app.ActionBarActivity;
	import android.view.View;
	import android.widget.TextView;
	/**
	* This app displays an order form to order coffee.
	*/
	public class MainActivity extends ActionBarActivity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_main);
	}
	/**
	* This method is called when the order button is clicked.
	*/
	public void submitOrder(View view) {
	display(1);
	}
	/**
	* This method displays the given quantity value on the screen.
	*/
	private void display(int number) {
	TextView quantityTextView = (TextView) findViewById(
	R.id.quantity_text_view);
	quantityTextView.setText("" + number);
	}
	}

view raw Do Something When Button is Clicked.java hosted with ❤ by GitHub

Tips : the gray words is the place you can place comments what ever you want. with /*_________*/
Tips 2:  google "comments java" and find some explanations inside the search page.

Second Modify the button's XML code, adds this sentence :
android: onClick="submitOrder"

H.W.