Apps PDF Renderer

package net.development.walkthroughs;

import android.graphics.Bitmap;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.pdf.PdfRenderer;
import android.os.Bundle;
import android.os.Environment;
import android.os.ParcelFileDescriptor;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import java.io.File;

public class MainActivity extends AppCompatActivity {

    private ImageView imageView;
    private int currentPage = 0;
    private Button next, previous;

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

        next = (Button) findViewById(R.id.next);
        previous = (Button) findViewById(R.id.previous);

        next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                currentPage++;
                render();
            }
        });

        previous.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                currentPage--;
                render();
            }
        });

        render();
    }

    private void render() {
        try {
            imageView = (ImageView) findViewById(R.id.image);
            int REQ_WIDTH = imageView.getWidth();
            int REQ_HEIGHT = imageView.getHeight();

            Bitmap bitmap = Bitmap.createBitmap(REQ_WIDTH, REQ_HEIGHT, Bitmap.Config.ARGB_4444);
            File file = new File(Environment.getDataDirectory().getPath()+"assets/1.pdf");
            PdfRenderer renderer = new PdfRenderer(ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY));

            if(currentPage < 0) {
                currentPage = 0;
            } else if (currentPage > renderer.getPageCount()) {
                currentPage = renderer.getPageCount() - 1;
            }

            Matrix m = imageView.getImageMatrix();
            Rect rect = new Rect(0, 0, REQ_WIDTH, REQ_HEIGHT);
            renderer.openPage(currentPage).render(bitmap, rect, m, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY);
            imageView.setImageMatrix(m);
            imageView.setImageBitmap(bitmap);
            imageView.invalidate();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="net.development.walkthroughs.MainActivity"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/image"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:scaleType="fitCenter"/>
  
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
      
        <Button
            android:id="@+id/previous"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="  Previous Page"/>

        <Button
            android:id="@+id/next"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Next Page "/>
    </LinearLayout>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="net.development.walkthroughs">

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

private void render() {
    try {
        imageView = (ImageView) findViewById(R.id.image);
        int REQ_WIDTH = imageView.getWidth();
        int REQ_HEIGHT = imageView.getHeight();

        Bitmap bitmap = Bitmap.createBitmap(REQ_WIDTH, REQ_HEIGHT, Bitmap.Config.ARGB_4444);
        File file = new File(Environment.getDataDirectory().getPath()+"assets/1.pdf");
        PdfRenderer renderer = new PdfRenderer(ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY));