From eb1e8d6e8b3462938e7b61d923ad608a7bcebb40 Mon Sep 17 00:00:00 2001
From: Timothy Johnson <_c_@mail.com>
Date: Wed, 16 Jul 2014 10:17:26 -0700
Subject: [PATCH 1/2] Correctly handle non-visible views.

---
 .../horizontalpager/HorizontalPager.java      | 21 +++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/com/github/ysamlan/horizontalpager/HorizontalPager.java b/src/com/github/ysamlan/horizontalpager/HorizontalPager.java
index 0ccc6cf..aa2ff92 100644
--- a/src/com/github/ysamlan/horizontalpager/HorizontalPager.java
+++ b/src/com/github/ysamlan/horizontalpager/HorizontalPager.java
@@ -138,6 +138,15 @@ private void init() {
         mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
     }
 
+    public int getVisibleCount () {
+        int count = 0;
+        for (int i = 0; i < super.getChildCount(); i++)
+            if (getChildAt(i).getVisibility() != View.GONE)
+                count++;
+
+        return count;
+    }
+
     @Override
     protected void onMeasure(final int widthMeasureSpec, final int heightMeasureSpec) {
         super.onMeasure(widthMeasureSpec, heightMeasureSpec);
@@ -175,7 +184,7 @@ else if (width != mLastSeenLayoutWidth) { // Width has changed
                             .getDefaultDisplay();
             int displayWidth = display.getWidth();
 
-            mNextScreen = Math.max(0, Math.min(getCurrentScreen(), getChildCount() - 1));
+            mNextScreen = Math.max(0, Math.min(getCurrentScreen(), getVisibleCount() - 1));
             final int newX = mNextScreen * displayWidth;
             final int delta = newX - getScrollX();
 
@@ -351,7 +360,7 @@ public boolean onTouchEvent(final MotionEvent ev) {
                         // Fling hard enough to move left
                         snapToScreen(mCurrentScreen - 1);
                     } else if (velocityX < -mDensityAdjustedSnapVelocity
-                            && mCurrentScreen < getChildCount() - 1) {
+                            && mCurrentScreen < getVisibleCount() - 1) {
                         // Fling hard enough to move right
                         snapToScreen(mCurrentScreen + 1);
                     } else {
@@ -383,7 +392,7 @@ public void computeScroll() {
             scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
             postInvalidate();
         } else if (mNextScreen != INVALID_SCREEN) {
-            mCurrentScreen = Math.max(0, Math.min(mNextScreen, getChildCount() - 1));
+            mCurrentScreen = Math.max(0, Math.min(mNextScreen, getVisibleCount() - 1));
 
             // Notify observer about screen change
             if (mOnScreenSwitchListener != null) {
@@ -410,7 +419,7 @@ public int getCurrentScreen() {
      * @param animate True to smoothly scroll to the screen, false to snap instantly
      */
     public void setCurrentScreen(final int currentScreen, final boolean animate) {
-        mCurrentScreen = Math.max(0, Math.min(currentScreen, getChildCount() - 1));
+        mCurrentScreen = Math.max(0, Math.min(currentScreen, getVisibleCount() - 1));
         if (animate) {
             snapToScreen(currentScreen, ANIMATION_SCREEN_SET_DURATION_MILLIS);
         } else {
@@ -443,7 +452,7 @@ private void snapToDestination() {
                 && ((screenWidth / FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE) < -deltaX)) {
             whichScreen--;
             // Check if they want to go to the next screen
-        } else if ((deltaX > 0) && (mCurrentScreen + 1 != getChildCount())
+        } else if ((deltaX > 0) && (mCurrentScreen + 1 != getVisibleCount())
                 && ((screenWidth / FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE) < deltaX)) {
             whichScreen++;
         }
@@ -475,7 +484,7 @@ private void snapToScreen(final int whichScreen, final int duration) {
          * RadioGroup used as "tabbed" controls. Also, make the animation take a percentage of our
          * normal animation time, depending how far they've already scrolled.
          */
-        mNextScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
+        mNextScreen = Math.max(0, Math.min(whichScreen, getVisibleCount() - 1));
         final int newX = mNextScreen * getWidth();
         final int delta = newX - getScrollX();
 

From 6af96bb3ca41bd35a82fb0e854bef661d5ea6ef9 Mon Sep 17 00:00:00 2001
From: Timothy Johnson <_c_@mail.com>
Date: Wed, 16 Jul 2014 10:21:54 -0700
Subject: [PATCH 2/2] Modified OnScreenSwitchListener to notify used before as
 well as after animation.

---
 .../ysamlan/horizontalpager/HorizontalPager.java    | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/com/github/ysamlan/horizontalpager/HorizontalPager.java b/src/com/github/ysamlan/horizontalpager/HorizontalPager.java
index aa2ff92..53f5c80 100644
--- a/src/com/github/ysamlan/horizontalpager/HorizontalPager.java
+++ b/src/com/github/ysamlan/horizontalpager/HorizontalPager.java
@@ -391,6 +391,12 @@ public void computeScroll() {
         if (mScroller.computeScrollOffset()) {
             scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
             postInvalidate();
+
+            // Notify observer about screen change
+            if (mOnScreenSwitchListener != null) {
+                int switchingScreen = Math.max(0, Math.min(mNextScreen, getVisibleCount() - 1));
+                mOnScreenSwitchListener.onScreenSelected(switchingScreen);
+            }
         } else if (mNextScreen != INVALID_SCREEN) {
             mCurrentScreen = Math.max(0, Math.min(mNextScreen, getVisibleCount() - 1));
 
@@ -503,6 +509,13 @@ private void snapToScreen(final int whichScreen, final int duration) {
      * Listener for the event that the HorizontalPager switches to a new view.
      */
     public static interface OnScreenSwitchListener {
+        /**
+         * Notifies listeners about the new screen. Runs before the animation completed.
+         *
+         * @param screen The new screen index.
+         */
+        void onScreenSelected(int screen);
+
         /**
          * Notifies listeners about the new screen. Runs after the animation completed.
          *