【Android Development for Beginners】Lesson 2A : Hook Up Two Buttons

This Notes is according to the udacity free course :

Android Development for Beginners

Lesson 2A : Hook Up Two Buttons

Today's class is to modify our JustJava app.

1. Add two buttons on the app.
2. Check out the layout style. 
3. Modify the xml for work.
4. Check out the initial value.
1. Quantity shows "2"
2. Price shows "10"

xml code :

	<?xml version="1.0" encoding="utf-8"?>
	<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="vertical"
	android:paddingBottom="@dimen/activity_vertical_margin"
	android:paddingLeft="@dimen/activity_horizontal_margin"
	android:paddingRight="@dimen/activity_horizontal_margin"
	android:paddingTop="@dimen/activity_vertical_margin"
	tools:context="com.example.android.justjava.MainActivity">
	<TextView
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:layout_marginBottom="16dp"
	android:text="Quantity"
	android:textAllCaps="true" />
	<!-- create a button called "+ -->
	<Button
	android:layout_width="48dp"
	android:layout_height="48dp"
	android:onClick="increment"
	android:text="+"
	android:layout_marginBottom="16dp"/>
	<!-- make sure the initial value is 2-->
	<TextView
	android:id="@+id/quantity_text_view"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:layout_marginBottom="16dp"
	android:text="2"
	android:textColor="@android:color/black"
	android:textSize="16sp" />
	<!--create a button called "-"-->
	<Button
	android:layout_width="48dp"
	android:layout_height="48dp"
	android:onClick="decrement"
	android:text="-"
	android:layout_marginBottom="16dp"/>
	<TextView
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:layout_marginBottom="16dp"
	android:text="Price"
	android:textAllCaps="true" />
	<!-- make sure the initial price is $10-->
	<TextView
	android:id="@+id/price_text_view"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:layout_marginBottom="16dp"
	android:text="$10"
	android:textColor="@android:color/black"
	android:textSize="16sp" />
	<Button
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:onClick="submitOrder"
	android:text="order" />
	</LinearLayout>

view raw Hook Up Two Buttons.xml hosted with ❤ by GitHub

java code :

if you want to add button's method, try to copy the "submitOrder" button.

	package com.example.android.justjava;
	import android.os.Bundle;
	import android.support.v7.app.ActionBarActivity;
	import android.view.View;
	import android.widget.TextView;
	import java.text.NumberFormat;
	/**
	* 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) {
	int quantity = 2;
	display(quantity);
	displayPrice(quantity * 5);
	}
	/**
	* This method is called when the increment button is clicked.
	*/
	public void increment(View view) {
	int quantity = 3;
	display(quantity);
	}
	/**
	* This method is called when the decrement button is clicked.
	*/
	public void decrement(View view) {
	int quantity = 1;
	display(quantity);
	}
	/**
	* 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);
	}
	/**
	* This method displays the given price on the screen.
	*/
	private void displayPrice(int number) {
	TextView priceTextView = (TextView) findViewById(R.id.price_text_view);
	priceTextView.setText(NumberFormat.getCurrencyInstance().format(number));
	}
	}

view raw Hook Up Two Buttons.java hosted with ❤ by GitHub