Creating Custom Horizontal Scroll View With Snap or paging
I have faced various issues to develop a horizontal scroll view with paging effect. I googled it a lot but not able to find anything satisfactory. Some search results help me, using those i have created my own custom horizontal scrollview class which can give similar effect as effect on Tablet Home page.

I will be discussing it step by step so that you can use it where required and it becomes easy for you to understand.

Step 1) Layout file – Simple layout file for demo

android:orientation=”vertical” android:layout_height=”match_parent”
android:layout_width=”match_parent” android:id=”@+id/layer”>

Step 2) CustomHorizontalScrollView – Class file which extends HorizontalScrollView and give snapping or paging effect.

public class CustomHorizontalScrollView extends HorizontalScrollView implements
OnTouchListener, OnGestureListener {

private static final int SWIPE_MIN_DISTANCE = 300;

private static final int SWIPE_THRESHOLD_VELOCITY = 300;
private static final int SWIPE_PAGE_ON_FACTOR = 10;

private GestureDetector gestureDetector;
private int scrollTo = 0;
private int maxItem = 0;
private int activeItem = 0;
private float prevScrollX = 0;
private boolean start = true;
private int itemWidth = 0;
private float currentScrollX;
private boolean flingDisable = true;

public CustomHorizontalScrollView(Context context) {
super(context);
setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT,
LayoutParams.FILL_PARENT));
}

public CustomHorizontalScrollView(Context context, int maxItem,
int itemWidth) {
this(context);
this.maxItem = maxItem;
this.itemWidth = itemWidth;
gestureDetector = new GestureDetector(this);
this.setOnTouchListener(this);
}

@Override
public boolean onTouch(View v, MotionEvent event) {
if (gestureDetector.onTouchEvent(event)) {
return true;
}
Boolean returnValue = gestureDetector.onTouchEvent(event);

int x = (int) event.getRawX();

switch (event.getAction()) {
case MotionEvent.ACTION_MOVE:
if (start) {
this.prevScrollX = x;
start = false;
}
break;
case MotionEvent.ACTION_UP:
start = true;
this.currentScrollX = x;
int minFactor = itemWidth
/ ConfigurationParams.SWIPE_PAGE_ON_FACTOR;

if ((this.prevScrollX – this.currentScrollX) > minFactor) {
if (activeItem < maxItem - 1)
activeItem = activeItem + 1;

} else if ((this.currentScrollX – this.prevScrollX) > minFactor) {
if (activeItem > 0)
activeItem = activeItem – 1;
}
System.out.println(“horizontal : ” + activeItem);
scrollTo = activeItem * itemWidth;
this.smoothScrollTo(scrollTo, 0);
returnValue = true;
break;
}
return returnValue;
}

@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
float velocityY) {
if (flingDisable)
return false;
boolean returnValue = false;
float ptx1 = 0, ptx2 = 0;
if (e1 == null || e2 == null)
return false;
ptx1 = e1.getX();
ptx2 = e2.getX();
// right to left

if (ptx1 – ptx2 > ConfigurationParams.SWIPE_MIN_DISTANCE
&& Math.abs(velocityX) > ConfigurationParams.SWIPE_THRESHOLD_VELOCITY) {
if (activeItem < maxItem - 1)
activeItem = activeItem + 1;

returnValue = true;

} else if (ptx2 – ptx1 > ConfigurationParams.SWIPE_MIN_DISTANCE
&& Math.abs(velocityX) > ConfigurationParams.SWIPE_THRESHOLD_VELOCITY) {
if (activeItem > 0)
activeItem = activeItem – 1;

returnValue = true;
}
scrollTo = activeItem * itemWidth;
this.smoothScrollTo(0, scrollTo);
return returnValue;
}

@Override
public boolean onDown(MotionEvent e) {
return false;
}

@Override
public void onLongPress(MotionEvent e) {
}

@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX,
float distanceY) {
return false;
}

@Override
public void onShowPress(MotionEvent e) {
}

@Override
public boolean onSingleTapUp(MotionEvent e) {
return false;
}
}

Step 3) TestHorizontalActivity- This class will be used as test class

public class TestHorizontalActivity extends Activity {

private LinearLayout linearLayout;
private CustomHorizontalScrollView horizontalScrollView;

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

int width = activity.getWindowManager().getDefaultDisplay().getWidth();
int height = activity.getWindowManager().getDefaultDisplay().getHeight();
horizontalScrollView = new CustomHorizontalScrollView(this, 3,
width);
setContentView(R.layout.horizontal);
linearLayout = (LinearLayout) findViewById(R.id.layer);
linearLayout.addView(horizontalScrollView);

LinearLayout container = new LinearLayout(this);
container.setLayoutParams(new LayoutParams(width, height));
// container.setHeight(height);

TextView textView = new TextView(this);
textView.setWidth(width);
textView.setHeight(height);
textView.setGravity(Gravity.CENTER);
textView.setText(“First Screen”);
textView.setBackgroundColor(Color.CYAN);
container.addView(textView);

textView = new TextView(this);
textView.setWidth(width);
textView.setHeight(height);
textView.setGravity(Gravity.CENTER);
textView.setText(“Second Screen”);
textView.setBackgroundColor(Color.GREEN);
container.addView(textView);

textView = new TextView(this);
textView.setWidth(width);
textView.setHeight(height);
textView.setGravity(Gravity.CENTER);
textView.setText(“Third Screen”);
textView.setBackgroundColor(Color.RED);
container.addView(textView);

horizontalScrollView.addView(container);
}

}

This is it, these 3 simple steps and you are ready to run a paging effect in your android application.

In next blog i will discuss how we can use combination of both horizontal scrolling and vertical scrolling.

I hope this post will be helpful.