package dani.cmp;
import android.content.Context;
    import android.graphics.Canvas;
    import android.graphics.drawable.Drawable;
    import android.view.KeyEvent;
import android.view.View;
     
    public class Zoom extends View {
            private Drawable image;
            private int zoomControler=20;
            public Zoom(Context context)
            {
                    super(context);
                    image=this.getResources().getDrawable(R.drawable.icon);
                    setFocusable(true);
                   
            }
            @Override
            protected void onDraw(Canvas canvas) {
                    // TODO Auto-generated method stub
                    super.onDraw(canvas);
            //here u can control the width and height of the images........ this line is very important
            image.setBounds((getWidth()/2)-zoomControler, (getHeight()/2)-zoomControler, (getWidth()/2)+zoomControler, (getHeight()/2)+zoomControler);
                    image.draw(canvas);
            }
            @Override
            public boolean onKeyDown(int keyCode, KeyEvent event) {
                   
                    if(keyCode==KeyEvent.KEYCODE_DPAD_UP)// zoom in
                            zoomControler+=10;
                    if(keyCode==KeyEvent.KEYCODE_DPAD_DOWN) // zoom out
                            zoomControler-=10;
                    if(zoomControler<10)
                            zoomControler=10;
                   
                    invalidate();
                    return true;
            }
    }

ackage dani.cmp;

import android.app.Activity;
import android.os.Bundle;
 
public class zooming extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(new Zoom(this));
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
</LinearLayout>