The answer is
As per the documentation :
Set the activity content from a layout resource. The resource will be inflated, adding all top-level views to the activity.
Your Launcher activity in the manifest first gets called and it set the layout view as specified in respective java files setContentView(R.layout.main);. Now this activity uses setContentView(R.layout.main) to set xml layout to that activity which will actually render as the UI of your activity.
You can set content view (or design) of an activity. For example you can do it like this too :
public void onCreate(Bundle savedinstanceState) {
super.onCreate(savedinstanceState);
Button testButon = new Button(this);
setContentView(testButon);
}
Also watch this tutorial too.
In Android the visual design is stored in XML files and each Activity is associated to a design.
setContentView(R.layout.main)
R means Resource
layout means design
main is the xml you have created under res->layout->main.xml
Whenever you want to change the current look of an Activity or when you move from one Activity to another, the new Activity must have a design to show. We call setContentView in onCreate with the desired design as argument.
Why setContentView() in Android Had Been So Popular Till Now?
setContentView(int layoutid) - method of activity class. It shows layout on screen.
R.layout.main - is an integer number implemented in nested layout class of R.java class file.
At the run time device will pick up their layout based on the id given in setcontentview() method.
public void onCreate(Bundle savedinstanceState) {
super.onCreate(savedinstanceState);
Button testButon = new Button(this);
setContentView(testButon);
show();
}
Set the activity content from a layout resource. The resource will be inflated, adding all top-level views to the activity.
- Activity is basically a empty window
- SetContentView is used to fill the window with the UI provided from layout file incase of setContentView(R.layout.somae_file).
- Here layoutfile is inflated to view and added to the Activity context(Window).
Source: Stackoverflow.com