How to create or develop a library or sdk in android. | How to build an AAR library in android.

To make your own library you have to do following thing:
1. making library for android needs parent app to run and access the library things.For this if you have already any project where u wants to make library that also fine or u can create a new android project and than do the following thing:-

To invoke SDK  we need to add this in our app gradle :-

dependencies {

compile project(':addnum')

}

To call the SDK first Activity or to inter inside the SDK we have do like following :-

addBtn.setOnClickListener(new View.OnClickListener() {
    @Override    public void onClick(View v) {
        // if u wants to pass any data to the SDK  sent it into bundle we can use all other method to do this        

Bundle bundle =  new Bundle();
        bundle.putString("name","Supriya");
        bundle.putString("id","123");
        Intent intent = new Intent(MainActivity.this,AddNumberActivity.class);
        intent.putExtras(bundle);
        startActivity(intent);
    }
});

 SDK code will be like following (AddNumberActivity) :-
to get the bundle from parent app :-

Bundle bundle = getIntent().getExtras();

if(bundle != null) {

String name = bundle.getString("name");
String id = bundle.getString("id");

}

tvname.setText(name);
tvid.setText(id); 

btnAdd.setOnClickListener(new View.OnClickListener() {
    @Override    public void onClick(View v) {
        if (ed1.getText().toString() != null && ed2.getText().toString() != null) {
            float result = Float.parseFloat(ed1.getText().toString()) + Float.parseFloat(ed2.getText().toString());
            tvResult.setText(String.valueOf(result));
        }
    }
});

Note:-

1. To generate .aar file please clean the project (Build > Clean Project ). 

2. And than Rebuild the project (Build > Rebuild Project ).

3. To see the .aar file please  choose view code as project.

4. And than click on sdk  addnum > build > outputs > aar. 

5. Here right click on .aar file and click on an option Reveal in Finder .

6. Now you can copy your .aar file to use in another project.