Android : How to change the image of an ImageView immediately after clicking a button?

Probably I am not doing it right. I was trying to change an image right after a button is clicked. But whatever way I follow, it takes about at least 1/1.5 seconds to get the changed image. I thought that might be happening because of the image size. But after reducing the size, still the problem remains. I tried to do as it is said in this link

But no luck. Still the image changes with a delay.

Can someone help me out with the right way?

Here is the code I used to change my image.

portrait.setImageResource(R.drawable.torch1);

after clicking the button, I want immediate change of the resource image.

here is the xml block I used to display the image.

<ImageView
        android:id="@+id/imageView1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_alignTop="@id/inside_imageview"
        android:layout_alignBottom="@id/inside_imageview"
        android:layout_alignLeft="@id/inside_imageview"
        android:layout_alignRight="@id/inside_imageview"  
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:soundEffectsEnabled="true"
        android:contentDescription="@string/desc"
        android:src="@drawable/on" 
        android:scaleType="fitXY"
        />

Thanks in advance for any help.