【Android Development for Beginners】Lesson 2A : Make the Quantity Picker Work

This Notes is according to the udacity free course :

Android Development for Beginners

Lesson 2A : Make the Quantity Picker Work

In Last Class we still cannot fix the problem to increase the coffee quantity automatic.
After the practice, now we can face the problem.



In this class, the most important concept is Global variable.
Keep it in your mind, it is the key word to fix the problem.

We use one pic to explain what the problem we face on.

We can see that "int quantity = 2" is exist in different code sequence with a complete brackets, they execute the action individually.

And Now, what we have to do is to level up the code " int quantity = 2" to a public class.

	/**
	* This app displays an order form to order coffee.
	*/
	public class MainActivity extends AppCompatActivity {
	int quantity = 2;
	@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 numberOfCoffees = 2;
	display(numberOfCoffees);
	displayPrice(numberOfCoffees * 5);
	}
	/**
	* This method is called when the order button is clicked.
	*/
	public void increment(View view) {
	quantity = quantity + 1;
	display(quantity);
	}
	/**
	* This method is called when the order button is clicked.
	*/
	public void decrement(View view) {
	int quantity = 2;
	quantity = 1;
	display(quantity);
	}

view raw Make the Quantity Picker Work.java hosted with ❤ by GitHub

Tips : When you create a global variable the words will turn into purple. If it is a local variable, it will shows up in black.


H.W.

The Code is create a GLOBAL VARIABLE and the "int quantity = 2" is under " public class MainActivity.

	/**
	* This app displays an order form to order coffee.
	*/
	public class MainActivity extends AppCompatActivity {
	int quantity = 2;
	@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 numberOfCoffees = 2;
	display(numberOfCoffees);
	displayPrice(numberOfCoffees * 5);
	}
	/**
	* This method is called when the order button is clicked.
	*/
	public void increment(View view) {
	quantity = quantity + 1;
	display(quantity);
	}
	/**
	* This method is called when the order button is clicked.
	*/
	public void decrement(View view) {
	quantity = quantity - 1;
	display(quantity);
	}

view raw Make the Quantity Picker Work_2 hosted with ❤ by GitHub

After the procedure, you can update the coffee quantity immediately.
Press Run and check out your application.