link textyou can set callback of Facebook Login in android default widget button or any View like below:-

buttonFbLogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mFbLoginManager.logInWithReadPermissions(LoginActivity.this, Arrays.asList("email", "public_profile", "user_birthday"));
        }
    });

Here buttonfbLogin is you button not Fb default button.

and below is FbManager and Callback

com.facebook.login.LoginManager fbLoginManager;

    fbLoginManager = com.facebook.login.LoginManager.getInstance();
    CallbackManager callbackManager = CallbackManager.Factory.create();
    mFbLoginManager.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
          // here write code When Login successfully 
        }

        @Override
        public void onCancel() {

        }

        @Override
        public void onError(FacebookException e) {
            // here write code when get error
        }
    });

Below link will help you better.

http://androidammy.blogspot.in/2015/09/facebook-login-with-custom-button.html

Let me know if stuck anywhere.

Happy Coding ;)

Hi Manmohan,

Hope this blog help you. http://findnerd.com/list/view/How-to-Customize-Facebook-Login-Button-On-Android/18725/