If you are looking to change the image or color of the widget when it is clicked or focused, Here is the code snippet that explains it:-

Step 1:- set the widget in an XML file for which you want to applying selector:-

<ImageView
     android:id="@+id/toolbar_home"
     android:layout_width="30dp"
     android:layout_height="30dp"
     android:src="@drawable/selector_home" >
</ImageView>

Step 2:- create an XML file under drawable folder as:-

<?xml version="1.0" encoding="utf-8"?>
  <selector xmlns:android="http://schemas.android.com/apk/res/android">
       <item 
            android:state_pressed="true"
            android:drawable="@drawable/greenhome" />
       <item 
           android:state_focused="true" 
           android:drawable="@drawable/homwhite"/>
       <item 
           android:drawable="@drawable/home" />
    </selector>

Step 3:- set on click listner in your main activity:-

 ImageView homeIcon=(ImageView) findViewById(R.id.toolbar_home);
   homeIcon.setOnClickListener(new View.OnClickListener() 
      {
       @Override
        public void onClick(View view)
         {
           Toast.makeText(getApplicationContext(), "Home Clicked", Toast.LENGTH_SHORT).show();
         }
        });