【 Android Development for Beginners】 Lesson 3A : Object Oriented Programming - 4

(I think Lesson 3A is the most important but also the most difficult part for beginner so far )

This Notes is according to the udacity free course :

Android Development for Beginners

Lesson 3A : Object Oriented Programming

Call Method on an objects

If We want to call a method on an object

object variable name.method name(input argument);
ex: titleTextView.setText("News");

You need to make sure you put a right object so you can call the method

By using object methods you can now change the attributes of different views, that you defined in XML, when the app is running and through user interaction.

reference :
利用程式碼更改文字顏色, setTextColor()
設定textview的顏色

Inheriting Behavior

KeyWord : findViewById, setContentView

findViewById & ContentView are methods, by not shown up the definition in the .java file.

so where are the definitions ? Ans: We inherited the code by using AppCompactActivity, and we can just extend it to MainActivity.

actually MainActivity is the extension for ActionBarActivity

actually MainActivity is the extension for ActionBarActivity（orange code is invisible)

If We don't want to use the older version of AppCompatActivity, we use @overide

to modify the code.

Concept between MainActivity and AppCompatActivity

REVIEWS

Create Java object(Link)

1. with constructor：
   object data type variable name = new object data type ( input argument );
2. with factory methods：
   object data type variable name = object data type . factory method (input argument);

call method on an object

1. object variable name . method name ( input argument );

set Data on Views

Quiz : Link

Tips : 

Nice work! You should start with calling findViewById to get access to the View object. Once that's been done, you can use the setText and setImageResource to change the text and the image.