CODEWITHSUNDEEP
android
Thanasis
Thanasis

Reputation: 439

Logic behind the creation of an Instance of a Button vs the creation of an instance of a plain Class?

I can't understand the logic behind the following code in android studio when we create an instance of a Button: 

Button btn = (Button) findViewById(R.id.btnRegister);

From what I know an instance of a class is defined like: MyClass myInstance = new MyClass(MyParameter)

If we apply the above logic the button code should be like this:

Button btn = new Button(findViewById(R.id.btnRegister));

But in fact the above code does not work. Why is "button" code so complicated to understand and does not relate to the code of a mere class? What does "(Button)" in brackets mean in the above example????

Thank you

Upvotes: 0

Views: 29

Answers (1)

Gabe Sechan
Gabe Sechan

Reputation: 93614

The find view line doesn't create a button. Your views are all created using the standard new syntax by the framework when you call setContentView. The setContentView function parses your xml and creates the appropriate classes. What findViewById does is search the views that it created in setContentView checking the ids for one with a matching id and returns it.

As for what (Button) does- its a standard Java cast. findViewById returns a View object. But some subclasses of View have advanced functionality not found on view. To use them, you have to have an object of the correct type. So you cast it to the correct type (which will throw an exception if it isn't the right type). For example you need to have a TextView to call setText, a normal View doesn't have that function.

Upvotes: 3

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