UI setzen über eigene Klasse

package de.jstk.iu_test;


import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;


public class MainActivity extends Activity {
    private static Context mContext;
    public static Context getContext() {
        return mContext;
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        mContext = getApplicationContext();
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        Button btn_button;
        btn_button = (Button) findViewById(R.id.btn_button);
        btn_button.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        Log.d("UI", "onClick: btn_button");
                        Test x = new Test();


                    }
                }




        );


    }


}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">


    <TextView android:text="@string/hello_world" android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/txt_text" />


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Test"
        android:id="@+id/btn_button"
        android:layout_below="@+id/txt_text"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />


</RelativeLayout>

package de.jstk.iu_test;


import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.TextView;


public class Test {
    public static View getRoot() {
        LayoutInflater inflater = (LayoutInflater) MainActivity.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        return (View) inflater.inflate(R.layout.activity_main, null);
    }
    Test()  {
        View r = (View) this.getRoot();
        TextView t = (TextView) r.findViewById(R.id.txt_text);
        Log.d("Test", "Inhalt des Buttons: btn_button --> "+t.getText());
        t.setText(new StringBuilder("Test"));
        Log.d("Test", "Inhalt des Buttons: btn_button --> "+t.getText());
    }
}