package com.example.b;

import java.io.IOException;
import java.io.InputStream;

import android.app.Activity;
import android.content.res.AssetManager;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;

public class BitMapTest extends Activity {
	String[] images = null;
	AssetManager assets = null;
	int currentImg = 0;
	ImageView image = null;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		image = (ImageView) findViewById(R.id.image);
		try {
			assets = getAssets();
			images = assets.list("");
		} catch (Exception e) {
			e.printStackTrace();
		}

		Button next = (Button) findViewById(R.id.next);
		next.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				if (currentImg >= images.length) {
					currentImg = 0;
				}
				while (!images[currentImg].endsWith(".png") && !images[currentImg].endsWith(".jpg") && !images[currentImg].endsWith(".gif")) {
					currentImg++;
					if (currentImg >= images.length) {
						currentImg = 0;
					}
				}
				InputStream assetFile = null;
				try {
					assetFile = assets.open(images[currentImg++]);
					BitmapDrawable bitmapDrawable = (BitmapDrawable) image.getDrawable();
					if(bitmapDrawable!=null 
							&& !bitmapDrawable.getBitmap().isRecycled()){
						bitmapDrawable.getBitmap().recycle();
					}
					image.setImageBitmap(BitmapFactory.decodeStream(assetFile));
					
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		});
	}

}

<LinearLayout 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:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <ImageView
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="image" />

    <Button
        android:id="@+id/next"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="next" />

</LinearLayout>