Context的作用

  protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
　　　　 
        TextView tv = new TextView(this);
        tv.setText(R.string.hello_world);
        setContentView(tv);
    }

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
      
        ImageView iv = new ImageView(this);
        iv.setImageResource(R.mipmap.ic_launcher);
        setContentView(iv);
    }